University of Central Florida

Senior Design Documentation

Brandon Devenport, Kai-Ta Huang, Jose Quinones, Diego Hurtado

Group 4

Fall 2015 – Spring 2016

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Table of Contents

1 EXECUTIVE SUMMARY 1 2 PROJECT MOTIVATION 2 3 PROJECT REQUIREMENTS AND GOAL 4

3.1 Lighting 4 3.1.1 Output Spectra 4 3.1.1.1 Daytime light output spectra 5 3.1.1.2 Nighttime light output spectra 6 3.1.2 Dimming 6 3.1.3 Intensity 6 3.1.4 Homogenous Light Output 6 3.1.5 Color Rendering Index 7

3.2 Optics 7 3.2.1 LED’s 7 3.2.1.1 LED optical power output 8 3.2.2 Reflective Surface 8

3.2.3 Diffuser 8 3.3 Electrical 8 3.3.1 Power Supply 8

3.3.2 Power Efficiency 9 3.3.3 PWM Driver 9

3.4 Hardware Housing 10 4 RESEARCH RELATED TO PROJECT DEFINITION 10

4.1 Division of Labor 10 4.2 Existing Similar Projects 12

4.2.1 Silk by Saffron 12 4.2.2 C-Sleep by GE 12 4.3 Relevant Technologies 13

4.3.1 Microcontroller 13 4.3.2 PWM Driver 14

4.3.3 Power Supply 16

4.3.3.1 Battery 16 4.3.4 PCB 17

4.3.5 Optics and Photonics 17 4.3.5.1 Thin Film Diffuser 17 4.3.5.2 LED’s 20

4.3.5.3 Ambient Light Photodiode 20 4.3.6 Heat management 23 4.3.6.1 Heat Sink 23 4.3.6.2 Thermal conducting material 23 4.3.7 Bluetooth Communication 24

4.3.8 Wireless Communication 25

4.3.9 Serial Communication 25

5. PROJECT HARDWARE AND SOFTWARE DESIGN DETAILS 26 5.1 Light 27 5.1.1 Auto Dimming 28

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5.1.2 Optics 29 5.1.2.1 Diffuser design 30 5.1.2.2 Reflector 32

5.3 LEDs 34 5.3.1 LED spectral range 34 5.3.1.1 The 390 nm to 499nm spectral range 35 5.3.1.2 The 500 nm to 599nm spectral range 36 5.3.1.3 The 600 nm to 699nm spectral range 38

5.3.2 LED placement configuration 40 5.4 Heat Sink 43

5.5 Software 44 5.6 Mechanical Design 45 5.6.1 Housing 45 5.6.2 Manual Dimming Switch 47

5.7 Electrical 47 5.7.1 Circuit Schematics 47

6 PROJECT PROTOTYPE TESTING AND CONSTRUCTION 48 6.1Component Test Procedure 48 6.1.1 Microcontroller 49 6.1.2 LED driver 49

6.2 Solar Spectra Acquisition 50

6.2.1 Data Processing 51

6.3 Light output 51 6.3.1 Spectral Matching 51 6.3.2 Intensity 51

6.3.3 Color Rendering Index 52 6.3.4 Homogeneous Lighting 52

6.4 Signal Processing 52 6.4.1 Interface 52 6.5 PWM code 55

6.6 PCB 56 6.7 Dimming 57

7 ADMINISTRATIVE CONTENT 58 7.1 Milestone 58

7.2 Budget and Finance Discussion 60 7.3 Mentors 61

APPENDIX A Written Authorization Bibliography

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1 Executive Summary

The SunLED project was born of an idea that the technology around us should not only enable us to perform amazing feats, it should also be able to improve our lives and the environments we live in. Based on the cutting edge of research that studies light-body interactions, the idea is to spur the new generation of indoor lighting. One that improves our performance and mood while helping our bodies stay in sync with the natural cycles of night and day.

Most modern sources of artificial light, that include incandescent and increasingly Solid State Light sources, are designed to provide comfortable and efficient ways to illuminate indoor spaces. With the advent of the LED, specifically the blue LED, the focus has shifted to energy efficiency, longevity, and in the professional and commercial settings to provide increasing CRI values and visually engaging light sources. While every year the industry makes clear gains in the areas mentioned above, there’s a lack of recognition of the inherent downside to blue LED based lighting technology: the visual and non-visual physiological and behavioral effects of continuous exposure to the shorter wavelengths of the visible spectrum in the human body.

To better solve this rising problem, a special type of LED light fixture will be designed, which is comprised of up to 35 LEDs that will be able to simulate the wavelength spectrum of natural sunlight throughout the day. In the initial phase of the product’s implementation into the market, clientele that will be targeted are nursing homes, assisted living facilities, hospitals, and commercial and government buildings where people stay indoors most of the time during the day.

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2 Project Motivations and Goals

2.1 Motivations

The NIH (National Institute of Health) defines circadian rhythms as “physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism’s environment.” Although, in the strictest sense, circadian rhythms refer to cyclical changes in hormones, body temperature, and other biological processes over the course of a 24 hour period, the term commonly is used to refer to the body’s natural sleep-wake cycle. Indeed, a disruption of a person’s circadian rhythms typically results in a disruption of the individual’s sleep wake cycle.

The circadian rhythm is a cluster of physical, behavioral and metabolic cycles of roughly 24 hours that occur in humans and most living organisms. Light interaction with retinal cells enables humans to see, but light also influences the circadian rhythm regulation of heart rate, alertness, hormone secretions, gene expression and core body temperature, therefore influencing health and productivity [1][18]. Research shows that while the retina’s cones and rods cells are the epicenter of the visual stimuli to the brain, light also excites a third kind of retinal receptor: the intrinsically photoreceptive retinal ganglion cells (ipRGC), or specifically within this cells, the photo pigment melanopsin [2][3]. This specific ganglion cells are very scarce within the retina but connect to all retinorecipient centers and deep structures of the brain such as the suprachiasmatic nucleus (SCN), the thalamus and the pineal gland [3][34]. The SCN regulation of the secretion by the pineal gland of melatonin, a hormone that regulates the circadian rhythm, has been found to be closely related to the activation or deactivation of the ipRGCs [4][30][32].

In the nature of human, melatonin production by the pineal gland reduce significantly in the morning, and stay low during the day, and then increases significantly in the later afternoon and evening. This daily hormonal cycle is strongly affected by light. Certain photoreceptor cells in the human eye, melanopsin retinal ganglion cells, are especially responsive to blue light with short wavelengths of approximately 460 nanometers. When exposed to high doses of bluish light, such as the sun, electric light, or LCD screen on electronic devices. These cells send a signal to brain to shut down the production of melatonin, and the brain will re-transmits this signal to the pineal gland. In this case with blue light, it reduces the body’s production of melatonin.

This effect of reducing body’s production of melatonin is naturally caused by sunlight during the day, blue light specifically. It can also come from other artificial light sources in the evening, such as electronic devices. This is could eventually affect sleep pattern and disrupt the sleep cycle because melatonin suppression in the evening.

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The activation of the ipRGCs and consequent melatonin secretion suppression has been shown to have a very distinct light spectral sensitivity in humans and other mammals. Studies have revealed that the melanopsin spectral peak sensitivity is around 447nm to 484nm [5][6][7]. This peak diverges from the retina’s cones and rods peak sensitivity of 555nm and 507nm respectively [14]. Melanopsin sensitivity is time dependent and has been shown to increase during nighttime hours. Studies show benefits in alertness and mood while being exposed to blue dominant spectrums during the morning and early afternoon [9][33], while also finding the benefits of red dominant spectrums during the late afternoon and night hours [10][14][15][25], matching the natural cycle of sunlight illumination.

While melanopsin sensitivity seems to be critical in understanding non-visual effects of light, melanopsin peak spectral sensitivity does not coincide in its totality with the spectral sensitivity of the ipRGCs [16][17], as a result it can be assumed that other photopigments contribute to the non-visual response to light in humans. These findings present a clear link between both the daily spectral shift of atmospheric sunlight and the physiological light-dependent cycles in humans, while also highlighting the inadequacy of white LED and other common modern lighting technologies as a suitable replacement to sunlight as seen by their spectral composition [15][18].

In the recent years with the fast advanced light-emitting technology such as smartphones further challenges human’s natural ability to maintain a regular sleeping cycle. Several studies have shown, that light exposure during night time can suppress the production of melatonin, which is secreted by the pineal gland. This suppression, which interrupts and makes it harder to fall asleep, wake on a regular schedule.

Disruptions in the circadian rhythm have been linked to diabetes, depression, sleep disorders, gastrointestinal disorders and cancer [11][12][13][31]. This proposal does not pretend to explore the many studies and experimental findings of circadian rhythm regulation on physiological processes and the effects of its disruption. We will however point out a number of studies in clinical settings that suggest the importance of circadian rhythm regulation in humans [19][20][21][22][23][24][26][27] [28][29].

The blue light has the highest effect on melatonin production levels, even regular room lighting has an impact to a degree. Conversely, light with longer wavelengths above 550 to 560 nm (warmer color) has a lower impact on melatonin production levels. So which means exposing to such light at night, in has a less disruptive effect on the sleeping cycle.

While the blue light may negatively affect our sleeping pattern, there are others methods to create lighting that can help maintain natural rhythms. For example, research shows that illumination of less than 30 lux for half an hour shouldn’t significantly drop the production of melatonin. Additionally, with a light source that have longer wavelength towards the warm color end of the spectrum will also

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reduce melatonin suppression that would otherwise be caused by a blue light, or even a traditional white light. Designing LED bulbs in this way can provide the illumination needed in the evenings and at night, but without significantly decrease the production of melatonin. Which will help maintaining a healthy sleeping pattern.

Despite the downside of having blue light in the evening which disrupt our circadian rhythm, such light during the day can actually help our body to maintain its natural rhythms. The light works to suppress melatonin at the same time the pineal gland is ramping down melatonin production in the morning. Design such an LED light source for the use during the day also can help an individual maintain a natural sleep cycle. So with the use of a high volume of bright, blue light in the morning with the use of longer wavelength light at night would be most efficient to help regulate the natural sleeping pattern.

3 Project Requirements and Goals

Despite a growing body of studies investigating light effects in humans, there’s is still a need to test optimal light conditions in terms of spectral composition and light intensity. Since most people in urbanized and modern societies are exposed to indoor lighting for most of the day, there’s need to provide efficient LED light sources that are sensitive to the physiological cycles and psychological needs of the human body. Our aim is therefore to employ multi-channel LED modules with real-time spectral tuning to construct sunlight matching spectral content of illumination for maximizing mood and cognitive performance, while minimizing disruption to biological rhythms. Our further aim is for the realization, demonstration of a final prototype that meet these optimization criteria for human health and performance.

In this section, the requirements and specifications for the main systems that were initially used in the project are detailed. These requirements were used as a basis for determining which specific components to select for more thorough analysis. This process was explored in the next section, titled Research Related to Project Definition.

3.1 Lighting

3.1.1 Output Spectra

The output spectra will be divided in two sections: day and night spectra. The day spectra will be focused on mimicking the solar spectra light distribution from sunrise to sunset while the night spectra will include only spectra within the range comprised from 550nm to 700nm. The night spectra will be constant during the night time, and it’s constrained to the spectral range described above with the purpose of avoiding triggering the melanopsin retinal response of the suprachiasmatic nucleus.

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Specifications: ● Visible Spectra Output between 300 nm to 700 nm ● Daylight spectral shift ● Shift rate of 1 spectra every 15 minutes from 9am to 4 pm ● Shift rate of 1 spectra every 1 minutes from 7am to 9 am and from 4pm to

6 pm ● Static spectra from 6pm to 7am

3.1.1.1 Daytime light output spectra

The daytime light output spectra will be completely defined by the experimental solar spectral data obtained. The only specification defining the daylight output will be to match as closely as possible the experimental spectral data seen in Fig 3.1.1.1-1 at each time point of the day.

Fig 3.2.1.1-1 Normalized Experimental Noon Solar Spectrum

Specifications: ● LED source’s spectrum appears as the sun’s spectrum ● Shifts over time ● Intensities within 25% at each wavelength data point

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3.1.1.2 Nighttime light output spectra

The night output light spectra will be defined by the constraints of the spectral range. The shape and intensity of this light will be defined by the light setting, while in schools and offices a dim a red dominated spectra would be sufficient, in hospitals due to nighttime activities in patient’s rooms a more intense and orange dominated spectra would be more ideal. In the final prototype a decision regarding spectral differences will have to be made.

Specifications: ● No spectral output below 550 nm ● Static spectrum throughout night ● No wavelengths in the infrared

3.1.2 Dimming

In order to improve the overall capabilities of the project, the light fixture will also contain the ability to dim, and this dimming effect will be optional. Either the user can manually dim the light using a set of switches or the LEDs will automatically dim remaining mindful of the ambient light already present in the room. There are a few options that can be used to allow for a manual dimming of the light and these options will be explored later on in the paper. For the auto dimming effect somewhere on the assembly a photodiode will be placed that picks up any ambient light present in the room and communicates with the microcontroller in order to reduce the intensity of the LED output by some scalar factor relative to the incident light. The automatic dimming effect would increase the projects energy efficiency since it would not need to always be at full intensity all of the time. This smart capability added to the project shows its ability to consider the users of the product and how they might be affected both in terms of energy consumption and maintaining an equal amount of lighting in the environment.

Specifications: ● 4 steps of dimming: Max, Mid-high, Mid-low, Low. ● A fifth step above Max to disable auto dimming.

3.1.3 Intensity

It is important to be mindful of the intensity of the output of the LEDs. Light that is too intense can cause negative effects. Like staring at the sun is not good. The intensity would of course not be near that of the sun. To limit the intensity to a value, it should not exceed 1000 lux.

3.1.4 Homogenous Light Output

The desired goal is that the materials used for scattering the light and diffusing the light are effective to the extent that the LEDs be indistinguishable from one another

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and the individual colors be sufficiently mixed. An undesirable result due to inadequately homogenizing the light output from the various LEDs is interference patterns at eye level (approximately two meters).

Specifications: ● No distinguishable individual LED outlines at the diffuser interface. ● No distinguishable individual colors at the image plane

3.1.5 Color Rendering Index

For quantifiable measurements of the accuracy of the project, the color rendering index or CRI of the LED bulb should be 99.99 during the day. This is because the light should somewhat match the spectrum of the sun as close as possible thus the CRI should be close to that of the sun as well. At night the color rendering index will be intentionally reduce in order to comply with the night spectrum, as long as the spectrum meets the specifications set out in the LED section.

Specifications: ● Color rendering index above 98%

3.2 Optics

3.2.1 LED’s

The challenge to create a solar simulator using LED has been present since the conception of LED technology. Solar simulators have been needed to test materials, solar panels, military technology, and many other uses. In the past solar simulators have been constructed using a combination of halogen, mercury, fluorescent and incandescent lights and for the most part they have created very accurate representations of the AM 1.5 spectra, which is used as the standard for equipment solar testing. To recreate the solar spectra with LEDs the challenge has been to overcome their narrow spectral nature. Each LED has an approximate Gaussian spectral distribution and as such it has a peak wavelength and full width half maximum, which describes the bandwidth of the spectral output. Most of the problems are found in the spectral range from 530 nm to 650 nm due to the lack of materials that efficiently produce light in that range. This project requires LEDs that cover the visible spectra and because of that, we need to use as many LEDs as possible to cover the spectral range from 400 nm to 700 nm. Only then the output spectra described in part 3.2.1 will be recreated.

Specifications: ● 25 to 35 individual LED channels. ● Multiple LEDs on each channel as needed.

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3.2.1.1 LED optical power output

To produce the adequate amount of candelas per meter and also to provide room for several levels of optical dimming. Because of this the ideal type of LEDs will be ones that are high power because it will allow more optical power without using many LEDs per channel and helping also with thermal management due to the decrease in the amount of LEDs.

Specifications: ● Optical intensity between 800 and 2000 lux.

3.2.2 Reflective Surface

The optics of the project is constrained by the size of the housing. A larger scattering surface and greater light propagation allows for a more accurate representation of the specifications, but it can only be so large for practical application. The budget also constrains the materials that can be used, and the size and design of those materials.

Specifications: ● Use standard reflective surfaces to allow light propagation towards diffuser.

3.2.3 Diffuser

The diffuser would need to fit within the square fixture such that all light emitted from the LEDs and scattered by the scattering surface would pass through the diffuser in order to have a more uniform light output as specified.

Specifications: ● Use a non-absorbing material nanoparticle to create a thin film. ● Nanoparticle size less than the inverse of the wavelength to the fourth

power ● Thin film thick enough to create Rayleigh scattering. ● Thin film thin enough to allow ballistic light.

3.3 Electrical

3.3.1 Power Supply

The system was to have a wide range of and large amount of components. Mostly are PWM drivers which feed the power to the LED diodes. A computer power supply will be used, as it serves as the AC to DC convertor, also it will reduce the voltage to appropriate values for the PWM drivers around 9-12 volts depending on the number of LED diodes in that specific PWM driver. The Arduino is normally powered by an AC adaptor which outputs 9V DC. However in this case, the power

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will also be delivered from the PC power supply. The entire system will be connected to a wall outlet to feed the power for each components in the system.

3.3.2 Power Efficiency

LED lighting is very different from incandescent and compact fluorescent lighting. It is more efficient, durable, versatile and energy saving. LED lighting products use light emitting diodes to produce light in a very efficient way. LED diodes can be operated at various currents. The typical baseline is 350 mA, 700 mA, 1000 mA, or higher drive currents are also available. Higher current increases the lumen output, but it also decrease in efficacy. Energy efficiency proponents are accustomed to comparing light sources on the basis of luminous efficacy. To calculate the lm/W, divide lumens by current times volts. For example, assume a diode with flux at 45 lm, operated at 350 mA and voltage of 3.42 V. The luminous efficacy of the LED diode is: 45 lumens/(.35 × 3.42) = 38 lm/W. To include typical driver losses, multiply the result by 0.85. Which gives 32 lm/W. The reason is LED light output is very sensitive to temperature, some manufacturers recommend de-rating luminous flux by approximation 10% to account for this thermal effects. However, in real world application, heat sink plays a big role on thermal performance as well as the design of the housing. This calculation is still a rough approximation. A more accurate measurement can will be obtained at the luminaire level.

Specifications: ● Be at least as efficient as an equivalent incandescent light bulb.

3.3.3 PWM Driver

PWM driver is chosen because of its characteristic and ability of dimming the light out without shifting the wavelength. For each type of LED diode with unique peak wavelength will be paired in series and connect to a single PWM driver. The PWM driver will be able to run up to 16 LED’s at 60V input, and the current to each LED diode will be from 300mA to 450mA. Also fine current adjustment can be done by connecting a resistor.

Specifications: ● Output of at least 700 mA of current. ● Have a PWM frequency of more than 200 Hz ● Support up to 16 LEDs per channel ● Able to “talk” to MCU

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3.4 Hardware Housing

Since the targeted clienteles are hospital, and commercial companies. The housing of the LED’s will be mounted on the ceiling panels on either standard sizes of 2x2 or 2x4 ft. With the integrated PCB circuit, power supply, heat sink, LED diodes and optical components fitted in the cutoff of the ceiling panel.

Specifications: ● Allow for standard installation in target settings. ● Big enough to support rest of the hardware ● Integrated light reflectors and diffuser preferred

4 RESEARCH RELATED PROJECT DEFINITION

4.1 Division of Labor

The project had been split up according to Table 4.1.1 and Graph 4.1.2 given below. The tasks were divided according to estimated difficulty, and majors. Brandon is in charged with most of the optical related aspects such as the diffuser, lens and photodiode. Kai is responsible for power supply, AC to DC convertor, design of the circuit with integrated LED drivers, and lastly the production of PCB for final prototype. Diego will be in charged with the LED’s, heat management as well as mechanical housing. Jose will be the programing the software to control the brightness of the LED’s base on the time of the day.

Brandon Kai Diego Jose

Diffuser Power Supply LED’s Programing

Optics LED Driver Heat management

Communication

Photodiode PCB Housing

Table 4.1.1: Division of Labor

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Table 4.1.2: Flowchart with each responsibility

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4.2 Existing Similar Projects

4.2.1 Silk by Saffron

Silk by saffron was a LED based product launched on the Kickstarter website in June 2015. The original funding goal was set to 100,000$, by August 2015 the project had gathered $62,000 and had attention from publications like Popular Mechanics, Gizmodo and others. The basic principle behind the product was to simulate sunlight’s color perception through the day. The project gathered intense attention when it was first announced only to later fail due to the lack of hard science behind the claims from saffron that the LED based light bulb had any real impact in the circadian rhythm regulation of consumers. The main complaint was that being based in white LED technology, the triggering of the circadian rhythm retinal response was still present. The project eventually fail to reach market due to lack of funding.

Main characteristics: ● Regular socket LED light bulb ● Daylight spectral change between white LED and warm LED diodes. ● No special night spectra

4.2.2 C by GE

In late 2015, GE announced a new line of Bluetooth LED’s branded C by GE. It will be available to the market in early 2016. There are two types of C by GE bulbs. First is the C Life LED, user can dim or brighten the light output via Bluetooth on a smartphone. The second one which is more interesting, it’s called the C Sleep. Aside from basic on/off functionality, it offers three distinct color temperature settings designed to sync with sleep cycle by using blue shifted light in the morning and warm red shifted light at night. The change is automatic although is not clear if the cycle gets longer or shorter with the seasons. The same shortcomings found in the Silk can be found here. The underlying technology is white LEDs that have important wavelength spectral components below the 500 nm triggering the retina’s ipRGCs response. Having the backing of GE the product is in market.

Main characteristics: ● Backing of GE. ● Regular socket LED light bulb. ● Daylight spectral change between white LED and warm LED diodes. ● Warm LED used for night spectra.

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4.3 Relevant Technologies

4.3.1 Microcontrollers

Originally Arduino UNO was chosen for the testing phase, it contains the Atmel ATmega328 core processor. However, as the project progressed, it was determined that 14 digital output pins are simply not enough for the design. Estimate of 24 types of LED diodes will be used. Which means that there will be a need of 24 output channels from the microcontroller in order to send the PWM signal to each driver with each type of LED diode. The same type of LED diode may run in series. So larger microcontroller was chosen, Arduino MEGA.

Arduino MEGA, which contains the Atmel ATmega2560 as its core processor is chosen for this project for a number of reasons. First of all was its ‘ease of use’ factor. Besides the fact that it’s programming environment is beginner-friendly, the software and hardware are both well-documented, and there exist numerous pre-built libraries that would greatly help in the coding process. Of all the boards in the Arduino family, the Arduino MEGA was singled out because it contained all of the features that were needed. According to the datasheet, it has 16 analog inputs and total of 54 digital input/output pins, which can be used to connect the PWM drivers, in addition to a USB connection. For memory storage, it includes 8 KB of SRAM, 4 KB of EEPROM, and 256 KB of flash memory, although of that 8 KB are used by the bootloader to upload programs onto the board. Power is supplied through the USB connection; alternatively, an external supply is also acceptable, in the form of either batteries or an AC to DC adapter for use with a standard wall outlet. The allowed range of input voltage for the board to function correctly is 6 to 20V, although 7 to 12V was recommended for better results. A resettable polyfuse provides protection from shorts or too much current to the computer connected through the USB. Table 4.3.1.1 given below summarizes the main features of the board. Graph 4.3.1.2 shows the layout of the the microprocessor.

Microcontroller ATmega2560

Operating Voltage 5V

Input Voltage (recommended)

7-12V

Input Voltage (limit) 6-20V

Digital I/O Pins 54 (of which 15 provide PWM output)

Analog Input Pins 16

DC Current per I/O Pin 20 mA

DC Current for 3.3V Pin 50 mA

Flash Memory 256 KB of which 8 KB used by bootloader

SRAM 8 KB

EEPROM 4 KB

Clock Speed 16 MHz

Table 4.3.1.1: Arduino Uno specs from Atmel

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Graph 4.3.1.2: Atmega168 pin mapping specs from Atmel

Key features of Arduino UNO

● Ability of produce PWM output ● Available resources on existing/similar project ● Open source ● Pre-built library

Besides the Arduino that was chosen for the projects. There were several other options that were considered and compared.

The BeagleBone Black Development Board:

BeagleBone-xM was a new contestant in the DIY world market which has caused a great impact on the creative developers. The level of efficiency is very high for this device. But the biggest downside of this device was its cost which was very high compared to other MCU. So the manufacture announced a smaller version of BeagleBone-xM by the name of BeagleBone which price was also not yet what the developer wanted. Then a new version was introduced and is a true example of efficiency and cost effectiveness.

4.3.2 PWM drivers

The TPS92551 constant buck LED driver is chosen for this project is because of its characteristic and ability of dimming the light out without shifting the wavelength. It drives maximum 450mA LED current up to 16 LEDs in a single string (maximum 23W). It integrates all the power components including the power inductor. The

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TPS92551 provides a full turn- key, highly efficient solution for wide range of single string LED lighting applications with up to 95% power efficiency. It accepts an input voltage ranging from 4.5V to 60V and delivers a 350mA LED current as default. The LED current is adjustable from 300mA to 450mA by charging a single external resistor.

There will be LED diodes that require higher than 450mA current in order to reach its threshold. So two of the TPS92551 can be connected in parallel in order to deliver a combined current of up to 900mA. Both will be share the same PWM signal from the microcontroller. Below is the summary of each pin and its function for TPS92551 driver.

Pin Number

Name Description Function

1,2 LED+ Anode of LED string

Supply input and rail connection to the anode of the LED string.

3 DIM Dimming signal input

Dimming control signal input. Open to enable or apply logic level PWM signal to control the brightness of the LED string.

4 GND Ground Reference point for all stated voltages. Connect to the exposed pad of the package externally.

5 VREF Voltage Reference

Internal voltage reference output.

6 IADJ LED current adjustment

Fine tuning of the LED current by connecting a resistor between this pin and ground. Connect this pin to ground for factory preset current.

7 LED- Cathode of LED string

The current return pin of the LED string, connect to the cathode of the LED string.

EP Exposed Exposed thermal pad

Used to dissipate heat from the package during operation. Must connect to GND directly.

Table 4.3.2.1: Discription of each pin of TPS92551

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4.3.3 Power supply

A power supply unit converts AC from wall outlet to low voltage regulated DC power for the internal components. Recent developed personal computers usually use a switched-mode power supply. Most of the power supply unit can deliver between 150 to 600 watts of power, even more on some of the higher end model. The voltages are at either 3.3V, 5V or 12V which is suitable for this project’s application. The Advanced Technology eXtended (ATX) standard, was first introduced by Intel in the mid 90’s, has provided the foundation that the way in which power supplies have evolved till now. It was an improved designed over the previous Advanced Technology (AT) standard, ATX has set the standard of the power supply to deliver three DC power outputs at 3.3V, 5V and 12V. The Advanced technology based PC has a chassis' power button that was linked directly to the power supply unit. ATX introduced a system where the chassis' power-switch is connected to the motherboard via a wire instead. It allows other components such as hardware or software to wake the machine. Additionally the power supply's primary connection to the motherboard was redesigned to a larger, 20 pin, keyed connector to prevent any human error on mixing up.

4.3.3.1 Battery

For the project, battery may be needed for the remote photodetector which will measure the current ambient light brightness, and will send signal to the microcontroller unit to adjust the LED output brightness via pulse width modulation.

Alkaline Battery: This traditional type of battery is dependent on the chemical reaction of zinc and manganese. They usually have higher density and long life span of storage. The non-rechargeable version usually have higher voltage at 1.5V compared to the rechargeable version at 1.2V. The biggest benefit of alkaline battery is the affordability, however for the longer time application, it is still better to purchase other more advanced type of battery.

The rechargeable alkaline battery also have disadvantages of efficiency and voltage of the battery being declined after each recharge cycle. Also there will be added cost to purchase the charger.

Nickel Cadmium: It is another type of rechargeable battery. These were the popular batteries before lithium ion came to the market and eventually replaced them. The Nominal voltage for a cell of Nickel Cadmium is lowered at 1.2V which is the same as NiMH. However there’s a wide range of sizes and capacities. The discharge rate is also very high. The memory effect is also one of the downside of these batteries, they will at some point suffer a sudden drop in voltage. Some advantages of the nickel Cadmium is the longer time spans of discharging.

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Lithium-Ion: This is another type of rechargeable. These are the most popular batteries on the markets today. The energy densities is the highest for its weight and slow loss of charge and memory effect. Also very efficient in the amount of current they produce and have been very effective. Also very light weight compare to other types of battery. The cost is the major setback, as there is a high demand for these type of battery, which much the manufactures are able to raise the price for these. Another disadvantage of the lithium battery is that it is very easy to get damaged and needs a protection circuit to maintain safe operation. Lithium-ion battery usually runs at 3.7 V which is extremely high compared to the alkaline 1.5V or NiMH of 1.2V. 4.3.4 PCB

A printed circuit board (PCB) is a component made of one or more layers of insulating material with electronic conductors. The insulator is typically made on the base of fiber reinforced resins, ceramics, plastic, or some other dielectric materials. Currently, the main generic standard for the design of printed circuit boards, regardless of materials, is IPC-2221A. Whether a PCB board is single-sided, double-sided, or multilayer, this standard provides rules for manufacturability and quality such as requirements for material properties, criteria for surface plating, conductor thickness, component placement, dimensioning and tolerance rules, and more.

The width of the circuit conductors should be determined based on the temperature rise at the rated current and acceptable impedance. The trace should not melt during short surge currents that can develop in the circuit. This requires sufficient cross-sectional area of copper as a function of amps and seconds. The spacing between the PC traces is determined by peak working voltage, the coating location of the circuit, and the product application.

4.3.5 Optics and Photonics

4.3.5.1 Thin Film Diffuser

Technologies relevant to diffusing the output light must blend the light sufficiently enough such that the individual colors cannot be seen and that there are no interference patterns at the far-field. These can be any sorts of materials that appear white and hazy which cause the light that hits it to be distributed in a more even fashion. If worst comes to worst, a very basic and cheap thin film diffuser could be “frosty” looking scotch tape because it allows light to pass through it and scatters the light in the process. This is not ideal of course, but assuming the budget gets depleted it is a possibility since scotch tape runs about a dollar depending on the brand. Instead, more commercially used optical materials will most likely be used.

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Common diffuser materials: ● Polyethylene terephthalate (PET) ● Polycarbonate ● Acrylic

These materials are common in diffusers used these days, and each has their perks. Different materials work better for in different environments under different conditions. It is important to note that some of them reflect UV very well compared to others. Also the thermal stability of some of the materials are lower than others. Below Table 4.3.5.1 compares various characteristics of these three common materials.

Material UV Resistance

Thickness (in)

Thermal Stability (C)

Description

PET N/A or Excellent

0.005 - 0.007

80 Indoor lighting

Polycarbonate

N/A 0.02-0.03 80 Panels

Acrylic Excellent 0.06-0.12 60 Rigid

Table 4.3.5.1

Advantages for PET: ● Certain types block UV ● Currently being used for indoor LED lighting ● High thermal stability

Disadvantages for PET: ● Not all types block UV ● Not very rigid ● Thin

Advantages for Polycarbonate: ● Semi-rigid ● High thermal stability ● Used in panel diffusion

Disadvantages for Polycarbonate: ● Not UV resistant ● limited application

Advantages for Acrylic: ● UV resistant ● Rigid

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Disadvantages for Acrylic: ● Not very high thermal stability ● Thick

An interesting yet not as common material to use in this project for scattering the light emitted from the LED is titanium dioxide nano-spheres. Some materials such as silicon absorb in the visible wavelengths really well; whereas titanium dioxide scatters in this range and absorbs in the ultraviolet and infrared wavelengths. This is highly desirable for the application specified for this project. Scattering effects of materials on light can be used to homogenize the light output from the LEDs. There a multiple types of scattering but the main type of scattering that concerns this project is Rayleigh scattering, which occurs when the particle size is a lot smaller than the wavelength of light. The dependence of Rayleigh scattering on particle size can clearly be seen by using nanoparticles of titanium dioxide whose diameters are about a quarter of the wavelength of light incident on the material surface. The peak scattering of each wavelength of light peaks when the diameter of the particle is a 1/lambda^4 of the wavelength. This mean that when that the project requires a particle size range whose scattering covers the visible spectrum of light only. In fig 4.3.5.1-1 we can see how a particle of titanium dioxide of 25 nm in diameter scatters light in the visible spectrum. This scattering behavior is similar to the scattering of sunlight as it goes into the atmosphere and is the responsible of scattering the blue light part of the spectra more than the red.

Figure 4.3.5.1-1 Rayleigh scattering intensity of titanium dioxide particle

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4.3.5.2 LED’s

A light emitting diode, known as an LED, is a p-n junction semiconductor. LEDs have often been described as capable of generating “cold” light, referring to its low operating temperature. The 5mm LEDs usually are only 10● - 25● C warmer than the ambient temperature as opposed to an incandescent light source, which is up to several hundred degrees hotter under similar conditions. The material used to make an LED dictates the energy of the photons leaving the diode. Each wavelength of light has a certain amount of energy associated with the photons being carried. The closer the wavelengths are to the ultraviolet range and the shorter wavelengths, the more energy the photons contain. The closer the wavelengths are to the infrared range and beyond, the less energy they contain. The greatest amount of light generated by most LEDs is around its peak wavelength

The 5mm molded LED round lens was chosen due to its wide variety of wavelength options. A lot of time was spent seeking out information on many types of LEDs and their suitability for this project. It is powerful and small enough to fit easily into the array. High power LEDs require some type of cooling using air fins, whether natural convection or forced air. Having the round lens 15 also ensures that the light is semi-directional although this will not be enough to homogenize completely the light output.

There was not one company that manufactured all necessary LEDs for the array. This is due to the lack of materials for LED production. Most of the information available for the LEDs was only what was listed on the manufacturers’ websites under the LED’s specifications. This usually listed the peak wavelength, half bandwidth, operating threshold current, full width half max, the operating conditions at which the peak wavelength was achieved and the complete spectral data. Determining the needed LEDs was an estimated guess until actual data could be acquired during testing. This is the reason 19 LEDs were picked for our initial design and after testing we will have to either add or subtract other LEDs.

4.3.5.3 Ambient Light Photodiode

This section will discuss various devices that could be used to implement an auto dimming effect to the project. The photodiode is essentially a semiconductor material that is reverse biased such that when a photons hit the depletion region of the device the energy is absorbed and electron hole pairs are formed as a result. It is reversed biased in order to operate in the negative voltage and negative current region of the photodiode which would yield positive power. The photodiode will send a current to the microcontroller that is proportional to the amount of light hitting the photodiode (the more light incident on the photodiode, the more current). Looking first at the PIN photodiode, this simply uses a semiconductor material that is p doped and another that is n doped with an intrinsic layer in between the p and

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n type materials. Light incident on the depletion layer results in current flow due to the electron hole pair formation as shown in Figure 4.3.5.4-1 below.

Fig. 4.3.5.4-1 PIN photodiode

Considering how the PIN photodiode works, different materials yield different responses depending on various parameters. That being the case, taking a look at a few different types of semiconductor materials used in PIN photodiodes and their properties will assist in the selection of the diode that works best for this project. The three different materials to be compared are silicon (Si), germanium (Ge) and indium gallium arsenide (InGaAs). The parameters of PIN photodiodes that are relevant to this project are the wavelength range, the dark current, the responsivity and the bias voltage. The wavelength range of the material is important because the diode required for this project would have to pick up visible light. The dark current shows the amount of noise that can be expected. Knowing the responsivity shows how much current is put out by the photodiode versus the amount of power incident on the photodiode. The bias voltage is useful from an electrical standpoint in determining if the photodiode is even practical for use in this project constrained by the electrical specifications (see Table 4.2.2-1 below).

Parameter Unit Si Ge InGaAs

Wavelength range

nm 400-1100 800-1650 1100-1700

Dark current nA 1-10 50-500 0.5-2.0

Responsivity A/W 0.4-0.6 0.4-0.5 0.75-0.95

Bias voltage V 5 5-10 5

Table 4.3.5.4-1 PIN materials

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It is important to note that the wavelength range of the Si photodiode ranges from 400-1100 nm. This most likely be the material used since it is the only material that covers the visible spectrum of light. The other parameters do not vary far from each other as well.

Advantages

● not very costly ● readily available ● low voltage

Disadvantages

● weak ● slow response time

Next, another relevant photodetector is the avalanche photodiode or APD. The APD utilizes the breakdown voltage characteristic in semiconductor devices in order to produce current when photons hit the diode’s depletion region. Similar to the PIN photodiode, the APD is reverse biased and uses both p and n doped semiconductor materials as well as an intrinsic layer; however, the APD experiences gain. Unlike the PIN photodiode, the APD uses an extra p type region along with p+ and n+ regions an intrinsic layer. As a result, the conduction and valence bands of these different layers arrayed in a certain manner when reversed biased yields a downhill slope for the electrons to create an avalanching effect. This is depicted in Figure 4.3.5.4-2 below.

Figure 4.3.5.4-2 APD photodiode

Similar to the PIN photodiode, different materials result in different responses that will have an effect on the functionality of the APD. The materials the will be

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compared are Si, Ge, and InGaAs. Since this type of photodiode uses a different property of the semiconductor material, the Avalanche gain of the photodiodes will be compared along with the wavelength range, dark current, and bias voltage. The avalanche gain is relevant to this project in the case that the current output from a Pin photodiode is too small (see Table 4.3.5.4-2 below).

Parameter Unit Si Ge InGaAs

Wavelength range

nm 400-1100 800-1650 1100-1700

Dark current nA .1-1 50-500 10-50

Avalanche gain

- 20-400 50-200 10-40

Bias voltage V 150-400 20-40 20-30

Table 4.3.5.4-2 APD materials

Advantages

● Fast response time ● gain

Disadvantages

● high bias voltage

4.3.6 Heat Management

4.3.6.1 Heat Sink

A well designed heat sink is needed, and it is very important to dissipate the heat, because LED’s emits high energy (heat). It could potentially alter the accuracy of the output by shifting its color (wavelength) and decrease its longevity with the raise of temperature. The material of the heat sink will be aluminum as its high ability of heat conduction and low weight, and cost is relatively cheap compared to other material such as gold.

4.3.6.2 Thermal conducting material

A thin layer of thermal grease will be applied in between the surface of the LED diode and the actual heat sink. This layer will provide a mechanical strength to the bond between the heat source and heat sink. Most importantly it will seal the air gaps (spaces). The actual composition of the thermal grease usually consist of a polymerizable liquid matrix and large volume fractions of thermally conductive filler. Such as epoxies, silicones, urethanes and acrylates, solvent based systems, hot melt adhesives and pressure sensitive adhesive tapes are also available.

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Various thermal grease materials: ● epoxies ● Silicones ● Urethanes ● Acrylates ● Solvent based systems ● Hot melt adhesives ● Pressure sensitive adhesive tapes

Common types of filter materials: ● Aluminum oxide ● Boron nitride ● Zinc oxide ● Aluminum nitride

The thermal conducting materials usually have lower heat conductivity than metal heat sink, and if the material is applied excessively, it could further decrease the performance of heat conduction and ultimately defeat the purpose of have a well-designed heat sink. The main purpose of the thermal conduction material is to seal the air gap, so only a very thin layer will be needed.

4.3.7 Bluetooth Communication

Bluetooth is a very handy technology that helps to transfer files between two devices and provides a wireless connection between, for example, the computer and the keyboard, mouse, printer, and so on. And like any technology, that process of the exchanging information has its advantages and disadvantages.

The Bluetooth’s biggest downside can be attributed, perhaps, a large consumption of battery power, if we talk about mobile phones or laptops. Bluetooth also has a small range, that is, if we want to set up a wireless connection between a printer and a computer, they must stand by. Furthermore, Bluetooth can provide a file transfer between only two devices at once. And what is most unpleasant, Bluetooth may serve as a means of hackers to break into your network.

But fortunately, this technology has many advantages. And the first of them, of course, a wireless type of connection. And it is very convenient because it does not need any more to be confused in endless wires connecting the computer and the printer, keyboard, mouse and headphones. Bluetooth helps to get rid of the need to find a USB slot for flash cards when they are all occupied for communication with peripheral devices. Also, the setting up of such a connection is not difficult, since the technology is easy to install and use. Thus, every person, even with no special knowledge, can use Bluetooth for work and daily life. Moreover, this simple technology is absolutely free. So we do not have to pay at all for using this technology.

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Summing up, we can say that the Bluetooth wireless technology is very convenient and easy to use. And despite the drawbacks such as the lack of security and a large energy consumption in mobile phones, Bluetooth is gaining more and more popularity. And most likely, these disadvantages will be eliminated in the future and the technology will be improved.

4.3.8 Wireless Communication

The introduction of wireless technology has numerous benefits and some disadvantages. Due to wireless technology, it is possible to have a better coverage as individuals can carry their mobile phones and technological gadgets for communication. This is because, individuals no longer require cables to communicate or operate through wireless technology. Also, the transmission of information is more effective. Businesses and customers communicate regularly, and most of the sales can be conducted online. Additionally, direct access to data has been achieved through wireless technology. This is because there are more sites open to individuals working at home and thus, an experience of flexibility for productiveness. It is also cheaper to operate via wireless technology. The costs incurred for installation are minimal and thus, it is a more cost-effective technology. Moreover, through wireless technology, it is possible to invent new products, market and sell online. New opportunities can be achieved through the use of wireless technology as it offers flexibility in mobility and keep most individuals informed of any current news updates and knowledge. On the other hand, wireless technology has increased the rates of insecurity. This is evidenced by cyber-crimes that are continuously being committed, attacks from users that are not authorized. There are also several factors that have to be considered during installation of this technology. With the presence of other signals like signals from radio, it is possible to suffer from interferences that are likely to lead to poor communication or to some extent no communication rendering the technology useless at such instances. The transmission speeds also vary and can be slower than expected, and this makes the technology less efficient. Some operators do not provide wide coverage, and there are usually some regions that cannot access wireless technology.

4.3.9 Serial Communication

Serial communications involves the use of data transmission from a device to another peripheral device even without the use of a computer. Serial port communications involves the sending of data as one bit at a time as compared the parallel bus communication. The parallel bus communications send several bits together as a whole through several bus channels that are parallel to each other. The serial port communication has several advantages and disadvantages in the communication process.

Serial ports are more efficient when the transfer bits are low. The serial communication transmits eight bits each at its time which means that the

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transmission depends only on one cable. The serial cable is not as commonly used today in modern computers but still appears as the most compatible port for many peripheral devices. The cables are available in most common stores and considered cheaper and narrower as compared to the parallel cables. The port also allows full-duplex communication that involves flow of information in different communications at the same time. The reason for serial port to support full-duplex transmission is because the serial port communication has different pins for data sent and data received.

The main disadvantage of serial port communication is the rate of transmission is slower because the bits are transmitted as one bit at a time for the 8 bits. This means that serial port communication is 8 times slower in transmission. The use of serial port may also be expensive regarding data rates. Most communication engineers are familiar with the parallel port communication unlike serial port communication. The serial ports have been overtaken by parallel buses that are widely deployed. Failure in the system affects the entire transmission since it depends on one cable.

5 PROJECT HARDWARE AND SOFTWARE DESIGN DETAILS Below in Graph 5.1 is the illustration of the entire systems. It begins with the user turning on the device. The MCU will check the current time and produce an accurate output base on the sun spectra that was collected. The microcontroller unit will send the PWM signal to LED drivers, and the power supply which converts the AC to DC will provide the voltage that is needed to the driver depending on the number of LED diodes. Up to 16 same type of LED diodes can be connected in series and driven by the same LED driver. The LED diodes will emit the light and pass through the designed optical diffuser which unify the light output.

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Graph 5-1: An illustration of the system

At the same time, there will be a photodetector measuring the current lumen/brightness in the room and adjust the LED diode lumen output accordingly to save energy, as a bright room would not need much of a light versus a dark room. The photodetector will send the signal (voltage) to the microcontroller in order to adjust the intensity of the light output via pulse width modulation which will maintain the correct wavelength.

5.1 Light

This is the main components of our design. Is also the main user interaction component. This makes it critical in terms of design, specification compliance and

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it should be defined by the attention to detail. This section entails everything from the creation

5.1.1 Auto dimming

The team decided to add an auto-dimming effect to the LEDs. This will be done by implementing an ambient light photodiode into the assembly. This photodiode would be connected to the microcontroller in order to communicate with it. Essentially the photodiode will pick up any light coming into the same area in which the design project is illuminating and communicate with the microcontroller to have the overall intensity of the LEDs dim accordingly. In this section, the design of the implementation of the photodiode will be discussed as well as the overall process of photo detection in terms of this project. The flow chart below (Chart 5.1.1.1) helps explain the basic process of the automatic dimming effect of the photodiode relative to this design.

Chart 5.1.1.1 Auto dimming function diagram

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The photodiode will be placed on the outside of the lighting assembly facing the exact opposite direction of the LEDs. This is so that the light coming from the LEDs has as little of an effect as possible on the photodiode. If the photodiode does not come with a lens already, a small lens can be placed over the photodiode to increase the numerical aperture of the photodiode assembly. The wiring of the photodiode will run up the corner of the housing and to the MCU. The photodiode itself will be placed in the corner of the housing to increase visibility of ambient light as a whole. This is depicted in Figure 5.1.2.2.2 below using FreeCAD.

Fig. 5.1.2.2.2 Photodiode depicted in red.

5.1.2 Optics

The team decided to configure the light in such a way that it would fit into a ceiling tile location. A square ceiling tile is 48 inches in length and width. The depth of the assembly that holds the LEDs and the mirrors and the diffuser will be about 6 inches. This gives the project some dimensions to work with to come up with some schematics to better design the project. This section will be covering the design of the optics concerning the reflection and propagation of the light as well as the diffusion. Below is a flowchart which will help explain the order of events which the light will undergo (see Figure 5.1.3.1).

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Figure 5.1.3.1 Flow of light

5.1.2.1 Diffuser Design

In order to meet the specifications stated in the project definition section concerning the diffusion of the output light, the diffuser design will be discussed in this section. In order to scatter all of the light most effectively, the diffuser will be placed such that any light that will light up a given area will have to first travel through the scattering material. Therefore the diffusing screen will be placed at the bottom of the fixture such that when looking at the total assembly the viewer can only see the diffuser and the homogenized light. A free design software called FreeCAD was used to design a sketch of what the diffuser will look like with respect to the total assembly. In the design the diffusing screen is depicted as a partly transparent white plane; however, in the actual project the screen will not be transparent in this way but more so hazy. In the design the perspective is shifted because these devices are designed to be implemented into the ceiling. Therefore the entire assembly is essentially upside down. The design is shown in Figure 5.1.3.1.1 below.

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Figure 5.1.3.1.1 Red arrow pointing to the diffuser

Advantages

● simple design ● common fabrication ● durable

Disadvantages

● possible insufficient diffusion of light

Taking the diffuser material to be titanium dioxide nanoparticles deposited on a glass substrate, a square glass sheet cut to fit the desired design will be used as a sort of base for the particles to lie on so that they can be evenly distributed and spaced accordingly. Since the particles will not remain in their original location in which they were placed, an adhesive must be used to get them to stick to the glass screen. Ideally the adhesive will have to be transparent to visible light or thin enough so that it has little or no effect on the output spectrum. Once the particles have adhered to the glass, the screen can be placed in the desired location according to the design of the total assembly. Alternatively, using a pre manufactured polycarbonate sheet is plausible as well. In this case the cost would most likely be cheaper since the desired product would be more common. That being the case, all that needs to be done for this material is have it cut to fit the light fixture assembly. Once cut, it can be inserted in the respective location of the diffuser.

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Advantages ● excellent diffuser of light ● rigid

Disadvantages

● difficult to fabricate ● costly

5.1.2.2 Reflector

In order to utilize most of the light, mirrored surfaces will be used in one of two configurations. The first configuration is to simply place a mirror with a reflection of nearly one hundred at the top of the interior of the assembly such that any light travelling away from the diffuser will be reflected back down through it and out of the square assembly. The walls of the assembly interior will be mirrors as well with the same amount of reflection. This will essentially be a mirrored box with the LEDs located at the center of the top. In the FreeCAD design it is shown that there is no objects between the LEDs and the diffusing surface. The LED assembly as a whole is depicted as a sphere on top of a cylinder on top of a square which is located at the center of the box assembly. The viewpoint of the design is from the side of the assembly in Figure 5.1.2.2.1 below.

Figure 5.1.2.2.1

Advantages

● simple to design ● easy to prototype ● not very costly

Disadvantages

● short optical path length ● not much mixing of light

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The second configuration is essentially the first configuration with another optical component added between the LEDs and the diffuser surface. The idea here is to allow the light to blend more and travel a greater distance before leaving the assembly after passing through the scattering material. Keeping the same setup as in the first configurations, a curved mirror will be suspended between the LEDs and the diffusing plane using some sort of skinny metal wire rack as support. The mirror holder will be a reflective surface to minimize loss. This will allow the light to be reflected across and back up toward the mirrored ceiling which will in turn reflect the light back down through the diffuser. A similar design was used for this configuration as was in the first configuration; however, now there is a curved disc like shape suspended between the LED assembly and the diffusing surface. This curved disk is the mirror that will reflect the light back upward and across in order to create a longer path length for the light to travel. The design is shown in Figure 5.1.2.2.2 below where the viewpoint is taken from the side of the total assembly.

Figure 5.1.2.2.2

Advantages: ● Longer light path length ● Smaller packaging ● Better homogenized light

Disadvantages: ● Difficult design ● More costly ● More complex optics

Either set up would suffice for this project. In terms of simplicity, the first configuration would be easier to assemble since there are no suspended parts. Essentially this would just be a mirror box with the LEDs in the center. The downside is the fact that the LEDs are pretty directional, and depending on their orientation and spacing the light might not get scattered well enough to light the area in which the assembly is located thus the desired homogeneous output of light would not be achieved. This is partly due to the constraints placed on the depth of the assembly which does not allow the light to propagate far enough before reaching the diffuser. The second configuration, on the other hand, would

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allow the light to propagate a greater distance thus allowing the light to mix more before being scattered by the diffuser. The downside to this configuration is the added complexity of suspending the curved mirror in the desired location without damaging any of the electrical and optical components as well as the housing itself.

5.3 LEDs

Each LED picked for this project will be essential for matching the spectral output of the sun throughout the day. Part of the difficulty in building this spectrum is that the peak wavelengths are not quite as close as specified by the manufacturer. They were higher or lower than the nominal peak wavelength. A few voids will be noted in this paper where there was trouble in finding sufficient LEDs to fill these gaps in the spectrum.

5.3.1 LED Spectral Range

During the day the full spectral range of LEDs will be used, but at night only the 550 nm to 700 nm range will be used as mentioned in the research. Since there are different areas of interest within the spectral range, we will document the LED design in three distinct groups: 390 nm to 499 nm, 499 nm to 599 nm and 600 nm to 700 nm. Once all of the individual plots were made, all of the LEDs were combined using superposition. All spectral data were first cleaned up by deleting negative intensity values, since it is not possible to have a negative amount of photons leaving a light source. All LED intensities were summed up for each wavelength, this was important to do since not all LEDs have the same half-bandwidths and some LEDs have multiple peaks. To see the full spectral output of the LEDs chosen during the research face (see Figure 5.4.1.1).

Fig 5.3.1.1 Spectral Composition of chosen LEDs

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5.3.1.1 The 390 nm to 499 nm Spectral Range

The lower wavelength region of the visible light spectrum is a critical part of the daytime spectrum of the project because this region is very dynamic at the transitions from daytime to nighttime. Since the LEDs have not been acquired and tested yet concrete conclusions cannot be made as to the number of LEDs of each type of wavelength. This being the case, the numbers of them can only be estimated as of now. Once actual data can be obtained the number of LEDs can be determined. LEDs were chosen from various companies for their properties of peak wavelength and bandwidth, optical power, and manufacturer. For a complete list of all LEDs required for this section of wavelengths and their associated companies and properties see table 5.3.1.1.1 below.

LED Parameter Condition Value

395nm APG2C1-395 Forward Current 350 mA 350 mA

CW Output Power 55 mW

Peak Wavelength 395 nm

Forward Voltage 3.7 V

FWHM 22 nm

410nm APG2C1-410 Forward Current 350 mA 350 mA

CW Output Power 125 mW

Peak Wavelength 410 nm

Forward Voltage 3.65 V

FWHM 20 nm

420nm APG2C1-420 Forward Current 350 mA 350 mA

CW Output Power 130 mW

Peak Wavelength 420 nm

Forward Voltage 3.5 V

FWHM 20 nm

435nm APG2C1-435 Forward Current 350 mA 350 mA

CW Output Power 380 mW

Peak Wavelength 435 nm

Forward Voltage 3.5 V

FWHM 25 nm

450nm APG2C1-450 Forward Current 350 mA 350 mA

CW Output Power 430 mW

Peak Wavelength 450 nm

Forward Voltage 3.1 V

FWHM 35 nm

470nm APG2C1-470 Forward Current 350 mA 350 mA

CW Output Power 200 mW

Peak Wavelength 470 nm

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Forward Voltage 3.3 V

FWHM 35 nm

490nm APG2C1-490 Forward Current 350 mA 350 mA

CW Output Power 130 mW

Peak Wavelength 490 nm

Forward Voltage 3.3 V

FWHM 35 nm

Table 5.3.1.1.1 LED Specs in the 390 nm to the 499 nm range

The peak wavelength and the bandwidth of the chosen LEDs are crucial to this project. In order to match the spectrum of the sun the LEDs must be able to cover the same wavelengths in this regime as the sun does at the necessary relative intensities. Since the intensities along this section must be very dynamic the approximate output spectra must have a somewhat narrow linewidth in some sections to allow for tunability and a fairly broad one in others to fill in the gaps. The approximate output spectra of the chosen LEDs were graphed using MATLAB on a single plot of the relative intensities versus the wavelength of light in accord with the acquired specifications. This plot can be seen in Fig. 5.3.1.1.1 below.

Fig. 5.3.1.1.1

5.3.1.2 The 500 nm to 599 nm Spectral Range

The mid wavelength region is in constant use in this project. Many problems arise in regards to this regime with respect to the intensity at certain wavelengths of light, and these will be discussed shortly. Finding LEDs to cover this range of wavelengths is very difficult. Not very many companies have the LEDs with the necessary peak wavelengths and linewidths desired for full spectrum applications in the regime. The chosen LEDs with their respective companies, peak

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wavelengths and bandwidths, and optical powers have been plotted in Table 5.3.1.2.1 below.

LED Parameter Condition Value

505 nm APG2C1-505: Forward Current 350 mA 350 mA

CW Output Power 130 mW

Peak Wavelength 505 nm

Forward Voltage 3.5 V

FWHM 35 nm

515 nm APG2C1-515 Forward Current 350 mA 350 mA

CW Output Power 130 mW

Peak Wavelength 515 nm

Forward Voltage 3.4 V

FWHM 35 nm

530 nm LXZ1-PM01 Forward Current 500 mA 500 mA

CW Output Power 128 mW

Peak Wavelength 530 nm

Forward Voltage 3.05 V

FWHM 30 nm

567 nm LXZ1-PX01 Forward Current 700 mA 700 mA

CW Output Power 192 mW

Peak Wavelength 567.5 nm

Forward Voltage 2.85 V

FWHM 100 nm

590 nm LXZ1-PL02 Forward Current 700 mA 700 mA

CW Output Power 112 mW

Peak Wavelength 590 nm

Forward Voltage 3.05 V

FWHM 80 nm

Table 5.4.1.2.1 LED Specs in the 499 nm to the 599 nm range

When dealing with wavelengths in this section, it is important to consider the fact that there is not a wide range of choices as far as wavelength is concerned. Since these particular LEDs will be on continuously for both the daytime and the nighttime spectra they are a big part of the overall LED emission spectrum. In this particular section of the sun’s spectrum the intensities are all relatively flat. This being the case, the LEDs need to be able to fill the spectrum while maintaining its “flatness”. Unfortunately LEDs with peaks in the green wavelengths are scarce. The LEDs’ spectra were approximated and plotted on a single graph using MATLAB again and can be found in Fig. 5.3.1.2.1 below.

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Fig. 5.3.1.2.1

5.3.1.3 The 600 nm to 699 nm Spectral Range

The upper wavelength regime of the visible light spectrum more critical at the transition from daytime to nighttime and throughout the night. The spectrum of the LED output light here must be fairly flat considering the sun’s spectrum through the day. At sunset these wavelengths will see changes in the intensity and must be adjusted to keep up with how rapidly the sun’s spectrum changes as it sets. LEDs with peak emission wavelengths in the region have been chosen for their various properties. These properties such as linewidth, peak emission wavelength, and optical power can been found in Table 5.3.1.3.1 below.

LED Parameter Condition Value

617 nm LXZ1-PH01 Forward Current 500 mA 500 mA

CW Output Power 72 mW

Peak Wavelength 617 nm

Forward Voltage 3.05 V

FWHM 20 nm

627 nm LXZ1-PD01 Forward Current 500 mA 500 mA

CW Output Power 54 mW

Peak Wavelength 627 nm

Forward Voltage 2.2 V

FWHM 20 nm

650 nm APG2C1-650 Forward Current 350 mA 350 mA

CW Output Power 60 mW

Peak Wavelength 650 nm

Forward Voltage 2.1 V

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FWHM 35 nm

660 nm APG2C1-660 Forward Current 350 mA 350 mA

CW Output Power 60 mW

Peak Wavelength 660 nm

Forward Voltage 2.1 V

FWHM 35 nm

670 nm APG2C1-670 Forward Current 350 mA 350 mA

CW Output Power 60 mW

Peak Wavelength 670 nm

Forward Voltage 2 V

FWHM 30 nm

680 nm APG2C1-680 Forward Current 350 mA 350 mA

CW Output Power 60 mW

Peak Wavelength 680 nm

Forward Voltage 2 V

FWHM 35 nm

690 nm APG2C1-690 Forward Current 350 mA 350 mA

CW Output Power 60 mW

Peak Wavelength 690 nm

Forward Voltage 1.7 V

FWHM 30 nm

Table 5.3.1.3-1 LED Specs in the 599 nm to the 699 nm range

The LEDs in the section will be on through the day and night as well. Careful consideration must be taken so that the respective spectra of the LEDs cover the whole section so that there are no gaps in the output spectrum of the LEDs. This section can be covered pretty since there are LEDs on the market that fill the “warm” regime pretty well. MATLAB was used to graph the respective spectra of the LEDs on a single graph of intensity versus the wavelength. This is shown in Fig. 5.3.1.4-1 below.

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Fig. 5.3.1.3.1

5.3.2 LED Placement Configurations

In designing an LED light fixture, the placement of the LED diode with respect to the rest of the components is critical. From heat management, to electronics, and even light output, everything is design around the LED diode. In our particular design due to the presence of between 25 and 35 different color LED channels, the need to design the placement and spatial distribution of the individual LEDs is critical. Of all this factors light homogenization is of outmost importance in deciding the placement of the LEDS. The outcome of each of the placement scenarios will only be completely understand by testing. The first LED configuration that will be explored will be a flat square placement of the LEDs. The different color channels will need to be mixed so that each color is neighbor to a color wheel opposite, like for example red and green or orange and blue. This mixing will help in the homogenization of the light output without the need of external optics. A model of this configuration can be seen in Fig 5.3.2-1.

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Fig 5.3.2-1 LED Square Configuration

The next configuration is inspired by a regular light bulb. The LEDs are placed on a cone at the center of a parabolic concave shaped mirror that allows the light to homogenize as it bounces from the surface.

The benefits of this design are: ● The thermal management is more effective since the heat can be rapidly

transferred to the heat sink.

The disadvantages of this design are: ● The conic surface does not allow an easy distribution of the light ● It can create color broadening.

The model of this configuration can be seen in Fig 5.3.2-2. Notice also how much the mirror takes space, this can also complicate the placement of other optical components.

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Fig 5.3.2-2 LED “Bowl” Configuration.

The final configuration we will test is the placement of LEDs at the bottom of a reflective hollow cone. This is called a light pipe and is a tried and tested way to ensure complete homogenization of the light.

The benefits of this design are: ● Compact design ● Simplification of optical design

The disadvantages of this design are: ● Thermal management is complicated

The placement of the LEDs at the bottom on the cone means that the LEDs will be very close to each other and the thermal plate between them will have a highly concentrated heat source. We would probably need for this design to use liquid cooling which would consume more power and take a lot of space. Still this seems to be a low price to pay when one weighs benefits against disadvantages. The model of this configuration can be seen in Fig 5.3.2-3.

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Fig 5.3.2-3 LED Conic Configuration.

5.4 Heat Sink

The design of the heat sink for LED diodes is a complex matter. As seen in Fig 5.4-1, the outer layer is where the fins with large surface area will dissipate the heat. The inner cylinder with sockets are where the LED diode will be placed. To further improve the heat conductivity, a thin layer of heat conducting material will be applied in between the surfaces. Also an external fan may be installed near the heat sink to help better dissipate the heat that is generated from the high powered LED diodes.

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Fig 5.4-1: Design of the heat sink for LED diodes

5.5 Software

The figure below describes the block diagram the Arduino Microcontroller is going to be sending to each LED to be able to display the equivalent sun’s spectra. In order for the microcontroller to send data, the information gets received from a source of data, for this project a database. The Data get accessed from the database and sets the “pinmode” function in the code below with the corresponding LED to set the PWM for. The PWM is represents a part of the sun’s spectra in the code. The output parameter specifies that the LED pin is an output. After the pin gets set as output pin, the “analogwrite” function below passes in the pin number of the LED connected and the brightness level between 0-255 to set, so the spectra gets altered according to the time of day, for the current day. Finally, the fade amount describes how much every time the loop function runs, to fade the led, giving the LED a “fading” effect. This effect was added to the led to give the change in intensity a little more of a dramatic feel to the project. The delay function simply delays the change in intensity of the led enough so the human eye can see the change take effect.

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Figure 5.5-1 Logic of events to occur for the LED’s to get set with the correct

intensity.

5.6 Mechanical Design

5.6.1 Housing

The illustration below shows the mechanical housing. The square 2x2 panel will fit most of the commercial ceiling panel section. The inner empty portion is where the actual LED diodes will shine through with the designed diffuser which will unify the light output. The rest of the empty space in the housing will be fitted with other components such as PCB board, power supply unit, heatsink and fan.

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Graph 5.6.1: An illustration of the mechanical housing

Graph 5.7.1: An illustration of the mechanical housing (rear view)

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5.6.2 Manual Dimming Switch

Below is the illustration design of the manual dimming switch, which can overwrite the signals from MCU. The features include 5 different brightness setting, with the increment 20% from 0% to 100%. There will be another switch to turn on/off the auto dimming function. Which is connected to the photodetector and links to the MCU (see Graph 5.6.2.2).

Graph 5.6.2.2: An illustration of the manual dimming switch

5.7 Electrical 5.7.1 Circuit Schematics Below is a schematic of a circuit of single LED channel and with its respective PWM driver and single LED (Fig. 5.7.1.1).

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Fig. 5.7.1.1 Wiring Schematic

6 PROJECT PROTOTYPE TESTING AND CONSTRUCTION

6.1 Component Test Procedure

Because the project has so many different components and subsystems, it is essential to test each individually so as to pinpoint and resolve any specific issues before combining them together into a cohesive whole. The testing process is arranged so that the microcontroller and PWM driver testing can be done in parallel with the LED’s. Since all three procedures work relatively independent of one another. After each system testing had been successfully completed, they were integrated together for the testing of the entire system. The following procedures detail the specific steps necessary to test the hardware and software components. If the expected outcome does not occur, or does not include all of the conditions of success, the system under test must be subject to thorough analysis to determine the problem. When it is discovered and resolved, the same test was re-administered, and the cycle continued until a successful outcome was forthcoming.

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6.1.1 Microcontroller.

In the beginning of the project, Arduino UNO was chosen as the microcontroller for this project. Which served the purpose of researching and programing of coding which can send pulse width modulation signal to dim or brighten the LED without shifting the color temperature (see Graph 6.1.1.1).

Graph 6.1.1.1: First time successfully implemented the communication with the

microcontroller and LED’s with PWM signal.

6.1.2 LED driver.

The TPS92551 constant buck LED driver is chosen for this project is because of its ability of dimming the light out without shifting the color temperature. It can deliver a maximum 450mA current with up to 16 LEDs in series. For the first time, a simple circuit was designed in order to test the functionality of the LED. PWM signal is sent from the microcontroller and feed the signal to LED driver, and a external DC power source was used to serve as a temporarily power source, which eventually powers up the LED.

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Graph 6.1.2.1: First time successfully integrated the LED driver with the

microcontroller and LED diode and an external DC power source

6.2 Solar Spectra Acquisition

Gathering the solar spectra of a normal daylight was critical to the project. The light output of our device will be based solely on the data gathered in this step. The first step of gathering the spectral data was to choose the right spectrometer. The majority of the visible spectra spectrometers would do a decent job a gathering data, but we wanted data that was reliable near the 400nm and 750nm edges, which can be a challenge in most spectrometers. We chose to gather our data with an Ocean Optics Flame Spectrometer that has a spectral range sensitivity from 300nm to 1100nm. The process of gathering the spectral data was the following:

1. Download Ocean View to Windows computer. 2. Connect Flame spectrometer to computer using USB port. 3. Turn on Spectrometer 4. Point Spectrometer at sun by slowly reaching the angle of optical saturation

of the device 5. Collect spectra

Steps 1 to 3 were followed at the beginning of each session and the steps 4 to 5 were followed in three different patterns:

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● From 7am to 8am and from 5pm to 6pm spectra was collected every minute. ● From 8am to 9am and from 4pm to 5pm spectra was collected every 15

minutes. ● From 9am to 4pm spectra was collected every 30 minutes.

This pattern was followed due to the fact that the spectral composition of sunlight changes rapidly in early morning and late afternoon, while at midday the spectra changes more slowly. A sample of the measurement can be seen in figure 6.2-1

Fig 6.2-1 Normalized morning solar spectra

6.2.1 Data Processing

The data gathered from the sun’s spectra will be used to manipulate each LED’s intensity to match the spectra of the sun. To achieve this, the analog signals received from the sun, will be rigorously converted to discrete signals which the microcontroller will use to light up each individual LED. Once the analog data gets converted to digital, the result will be a graph depicting the intensity data points versus the wavelength of the spectra. This relationship gets stored in a relational database management system, consisting of one table with two columns, Intensity

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and Wavelength. Organizing the data this way, results in cleaner data throughput through the communicating channel. There are three different means of communicating to think about. There is Bluetooth, Wireless, and Serial Communications. Ultimately, the goal of the chosen communication channel is to reliably transmit the data with as much data loss and data error as possible. So, choosing the correct channel is essential. This can be achieved with the predefined Arduino libraries which makes it really easy to program in an efficient way without complex delay or timer/interrupt sequences. As important as choosing the most efficient communicating channel is the logic or the sequence of events the code will carry forth to LED’s so they can emit the sun’s spectra. The figure below describes the basic flow of events to mirror the sun’s spectra.

6.3 Light Output

6.3.1 Spectral Matching

This is the most critical testing of the project since is the main measurable outcome and the standard for failure. Light output will be tested in by using an Ocean Optics flame spectrometer in real time to collect the light bulb's spectra and compare it to the solar spectral input. The error margin between the two should at all times be kept below 25%. These methods will be used to match each spectrum throughout the day:

1. Normalize spectra obtained from the LEDs and the sun 2. Using MATLAB check percent error between the two normalized intensities

at each wavelength 3. If any intensities at a given wavelength yield a percent error of 25% or more,

then adjust spectra of LEDs accordingly using PWM 4. Repeat 1-3 until percent error is less than 25% 5. Repeat 1-4 for all spectra of the sun throughout the day.

6.3.2 Intensity

We will use two methods to understand the light intensity generated by the light fixture:

● Optical power measurements with an optical power meter ● Photodiode voltage meter

The main challenge will be to translate those measurements into a working standard like candles or lux. We will try to purchase or loan a candela meter that will solve this issue.

6.3.3 Color Rendering Index

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Testing the Color Rendering Index is a fairly standard process. The purpose is to ensure that the colors reflected out of objects when illuminated by sunlight are as intense that when illuminated by an artificial light source. The CRI of the sun is 100, and since the goal is to match the spectrum of the sun, this project should have a CRI of nearly 100 as well. Most white LEDs lamps have a CRI between 98 and 99 percent, so our design should be superior to those. To test the CRI we will use a relative method by comparing a photograph of a piece of paper that contains 16 different colors in direct sunlight and then in a dark room with our light source directly hitting the paper. If the CRI is low the colors in the paper will look washed out and not vibrant compared to when exposed to sunlight.

6.3.4 Homogeneous Lighting

The output light per the specifications must be sufficiently homogenized. Testing this involves a couple of steps which will be described in this section. Both tests involve the perspective of the viewer because the light must light up a room sufficiently and effectively while not causing any annoyances due to interference of light at the image plane and color dispersion. The first step is very elementary but also extremely necessary to meet the criteria set out in the goals and objectives. With the light raised up into the ceiling, the viewer should be about two meters away. When looking up at the light fixture the viewer should not be able to see the individual LEDs in the assembly and their colors. The light at the diffuser level should be at worst a point source in that plane. The ideal would be to get the entire diffuser surface evenly illuminated. The second step is to test the color dispersion in the image plane. The light hitting objects in the room should by no means be decomposed into individual colors. This phenomena is called color dispersion and is common in light sources that have

6.4 Signal Processing

6.4.1 Interface

Once the signal from the microcontroller reaches the LED’s and changes their intensity and the spectra, the next approach is to inform the user by means of some application whether it be a Desktop or mobile application that the LED’s have changed states as seen in Fig 6.4-1, according to the time of day and report any errors that arise.

The bluetooth interface will get implemented in the following ways: ● Bluetooth module arduino by adafruit ● Microcontroller connected to bluetooth ● A tablet ● An android application to read and write values to microcontroller

Wireless interface is getting implemented the following: ● Wireless module interface card

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● Microcontroller connected to wireless interface card ● A tablet ● An application to display data and send data back to micro controller ● A standard protocol for the wifi internet to communicate across wifi enabled

devices ● Disadvantage of wireless communication is that wifi signals tend to weaken

over longer distances or with multiple users accessing the network all at once, so ends up with packet loss and more time spent in retransmission of lost packets.

Serial communication is getting implemented the following ways: ● A usb to serial module connector ● Microcontroller to talk with computer through serial connector ● A Desktop computer capable of running a large scale application ● Correct cabling for serial port to computer ● Disadvantage of serial is that the amount of bits transmitted is once every

frame, so ends up with low transmission.

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Fig 6.4-1 Human interaction interface

6.5 PWM code

Figure 6.5-1 on the next page describes the code used Arduino environment to light up one led. This code works because it demonstrates all that is needed to input certain values into all the LED’s to be used and replicate the sun’s spectrum. With the following code, the purpose of this project will be accomplished.

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Figure 6.5-1 Code to fade one LED connected to arduino microcontroller

6.6 PCB

Currently it’s still at design and testing stage, however for the final product, a printed circuit board is required. It will appear professional and high quality. There are a few ways to design a printed circuit board with free software, such as Eagle Cad. Eagle Cad offers a free version which is plenty for the needs of this projection. The file type is also accepted by most of the manufactures. That being said, there are many resources out there for DIY printed circuit board, and the prices are fairly competitive. However, our team does not have any previous experience of design printed circuit board, and the decision has been made that it would be the best interest and time efficient to have the printed circuit board made by other readily available manufactures. Below are some of the popular manufactures that may be considered: 4PCB: Located in United States, and have student program for college students. In results the costs are fairly affordable to students. A 2-layer full spec printed circuit board would costs 33 dollars and 4-layer full spec would could around 66 dollars. Another plus side is that there is no minimum order requirement

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PCB-Pool: It is one of the popular online manufactures, the company is based in Canada and have great reviews among online communities. The price is a bit higher than 4PCB at 42 dollars for 2-layer and 100 dollars for 4 layer full spec printed circuit boards. Express PCB: As the named mentioned, expressPCB offers a very fast service, the turnaround time is guarantees at 2-day delivery. The price is very competitive as well at 51 dollars for a 2-layer and 99 dollars for a 5 layer. The shipping charged is 10 dollars for its express shipping. This would be a great option is time is very limited.

6.7 Dimming

In order to test the dimming of the LED module, the process is divided into two sections. First, the dimming controlled manually by a user that flips some sort of a switch is tested. Then the auto dimming effect of the assembly will be tested. The reason for this subdivision is due to the fact that these two processes are somewhat independent of one another to an extent. Below is a block diagram of the process of testing both in Fig. 6.6.1:

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Fig. 6.6.1 Dimming Action Process

7. Administrative Content

7.1 Milestone

During the first semester, extensive research was done on previous similar projects and technology, so that the group could find potential different approaches to achieve its overall project goals also achieve a better accuracy, and to expand its knowledge on the matter.

In addition, a detailed design had to be finalized for the whole system. To maximize the functionality of the project, a great amount of time had been spent on research, looking into different types of electronic and LED components that could be most successful to meet the project specifications. The group was also aware of the difficulties that might be encountered while constructing the system. In order to avoid last minute problems, the decision was made to start the most important, also the most difficult part of the project during winter break. That encompasses both the software, electrical and optical aspects of the project.

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In the electrical aspect, a low power LED with PWM driver system was set up in the beginning of the project in order to test the coding which was designed in order to dim or brighten the LED via pulse width modulation. A proper power supply is needed in order to feed all the power components in the system. That’s when the group decided to look into a PC power supply. It serves as the AC to DC convertor, also it will reduce the voltage to appropriate values for the PWM drivers around 9-12 volts depending on the number of LED diodes in that specific PWM driver. The Arduino is normally powered by an AC adaptor which outputs 9V DC. However in this case, the power will also be delivered from the PC power supply. The entire system will be connected to a wall outlet to feed the power for each components in the system.

In the optical aspect, during the first semester, the data of daily output spectra of the sunlight was collected via a handheld photodetector. Then the data was simulated on Math Lab in order to calculate the number of each LED diodes is needed to achieve and match the output of sunlight.

The overview of the schedule for the first semesters as seen in Table 7.1.1 is laid out in the table below. The first semester was focused largely on the research and report. In addition, a few components were acquired and began testing on the software with simple circuit. The second semester will be devoted to the physical construction and completion of the construction, with the second half of the semester focused on testing the system, and achieve accuracy.

Week Date

1 8/24/2015 Individual Project proposal

2 8/31/2015 Group formed

3 9/7/2015 Group project proposal

4 9/14/2015 Break down the project into small sections

5 9/21/2015 Research on each section

6 9/28/2015 Individual research

7 10/5/2015 Acquired funding

8 10/12/2015 Design PWM code

9 10/19/2015 Acquire testing components (MCU, drivers, LED’s)

10 10/26/2015 Documentation

11 11/2/2015 Consulted with Mr. Will Huang (mentor)

12 11/9/2015 Software testing

13 11/16/2015 Schematic project diagram

14 11/23/2015 Final draft report

15 11/30/2015 Order optical components

16 12/7/2015 Final report

Table 7.1.1 Milestone calendar

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7.2 Budget and Finance Discussion

At the conception of this project, it was evident that the financial burden would not be light, due to the large amount of components required and the complex technology needed to implement such a design. Especially high powered LED’s and PWM drivers are expensive due to the amount that will be needed for this project. For these reasons, the group decided to look for a sponsor to handle most, if not all, the relevant expenses. However, the group was limited by the fact that many of the companies willing to sponsor projects already had a project design in mind. Fortunately, there was a company that allowed senior design groups the creative freedom to develop their own designs, as long as they fell within the general categories specified by the company. Boeing/Leidos was the company that sponsored the group with $899.46

The budget, shown in the table below, was approved for full funding from the company, with the stipulation that the group would purchase the products themselves and then receives reimbursement for submitted receipts.

In addition to the specific hardware and optical components needed to construct the project, it was known that a large amount of additional equipment would be necessary for testing purposes, such as a multimeter, oscilloscope, a power supply, and a photodetector. The facility provided for senior design students was the Senior Design Lab, where much of this equipment was available for student use. Some of the equipment were also obtained and borrowed from CREOL. The project also required smaller circuit components for building the PCB prototype, such as resistors, capacitors, diodes, and wires, as well as the soldering tools needed to secure them to the board. The soldering tools were available in the lab, but many of the components the group had to obtain itself. Also included in the budget was the price for manufacturing the PCB itself. The group decided to have 2 copies made as a precaution in the future, in case the first one broke or was otherwise rendered inoperable.

Before the funding was approved, the group has discussed each of the 4 members contributed $50, total of $200. The purpose of the personal funding was to allow the project start early. A small portion of the money was used to purchase the first microcontroller, Arduino UNO, which allow us to start research and develop the coding for PWM drivers. Some of the PWM drivers were also received from Texas Instrument as samples. Which have been used along with the Arduino UNO to test the coding. See Table 7.2.1 for the power budget.

Item Qty Unit Price Total Price

Microcontroller Arduino UNO 1 $25 $25

LED’s 50 $8.5 $425

PWM drivers 15 $4.5 $67.5

Misc 1 $100 $100

Housing 1 $75

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Table 7.2.1 Estimated Project Budget

7.3 Mentors Will Huang M.S. is chosen as the project mentor, who is also a relative of teammate Kai Huang. Will Huang is working as a Senior Electronic & Payload engineer who has strong track record of performance for Northrop Grumman. He provided system engineering expertise to the team by helping troubleshoot issues as they arose in actual fleet use of the system and proposed solutions through team conversations to resolve or mitigate the issues. He leads the LIDAR system Integration in the foreign nation. He is also a fellow University of Central Florida graduate. He obtained a bachelor in electrical and electronics engineering in 2003. He further pursued graduate program at CREOL and obtained a master of science in Optics.

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APPENDIX A Written Authorization Authorization given by Atmel Corporation

From http://www2.atmel.com/About/legal.aspx, it states that “Materials from this website www.atmel.com and any other website owned, operated or controlled by Atmel and/or its affiliated or subsidiary companies (together, Atmel) are owned and copyrighted by Atmel. Unauthorized use of such Materials (e.g., information, documentation and software), including these Terms, may be a violation of Atmel's intellectual property rights or other applicable laws. If you agree to these Terms, you may download (on a single computer), copy or print a single copy of all or a portion of the Materials for informational, non- commercial, lawful purposes only.” Since this documentation is only for academic and non-commercial purpose, the materials are deemed to be licensed to the group.

Authorization given by Microchip From_http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=487&param=en023282 ttp://tinyurl.com/microchip-com, it states that “If you use Microchip copyrighted material solely for educational (non-profit) purposes falling under the “fair use” exception of the U.S. Copyright Act of 1976 then you do not need Microchip’s written permission. For example, Microchip’s permission is not required when using copyrighted material in: (1) an academic report, thesis, or dissertation; (2) classroom handouts or textbook; or (3) a presentation or article that is solely educational in nature (e.g., technical article published in a magazine). Please note that offering Microchip copyrighted material at a trade show or industry conference for the purpose of promoting product sales does require Microchip’s permission.” Since this documentation is only for academic and non-commercial purpose, the materials are deemed to be licensed to the group.

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