Muhamad Sohimi IbrahimEngineer: Sensors and Display
Chidum OkoyeEngineer: Lighting
AbstractA seed starter kit is a device that has the ability to germinate seeds indoors with the ability to record soil
moisture, temperature, and light data. The device has been developed for a local non-profit called Rochester Roots and Montessori school. Since Rochester, NY has very harsh non-farming seasons, this device allows the seeds to grow inside and later be moved outside to a garden when the weather is suitable for farming. A MSD team developed this device last year but was not able to measure lighting and moisture, is not modular, nor stackable. The goal of this project is to create a unit that can be easily stacked, dimensioned for use in school and home, and to measure the aforementioned quantities. The end result will build upon the original design while improving its range of capabilities while reducing production costs. The resulting product will meet the specifications set by the Rochester Roots and will be their intellectual property.
IntroductionRochester Roots, a local non-profit organization, in conjunction with the Montessori School in the Rochester
City School District requested a seed starter kit to be built to help educate students on the life cycle of plants. A seed starter kit is a semi-enclosed unit that allows the user to place seeds inside the unit and monitor aspects of their growth with the goal of planting during the harsh winter and transplanting them outside in the spring. A previous MSD team (P15419) designed a unit which housed the seeds properly and functioned well. Rochester Roots has requested that a modified unit be developed which has a light physically attached to the unit, smaller in size for counter top use, stackable, and able to monitor and output selected data. The unit is able to measure light, temperature, and soil conditions.
The goal of this project is to redesign the unit housing to make it easier to stack for efficient use in the classrooms or at homes, integrate controlled lighting, add more data monitoring for soil moisture, temperature and light. The end result will build upon the original design while improving its range of capabilities while reducing production costs.
Design ProcessThe Seed Starter Kit that was designed is a second iteration of a design started by a different group last
year. At the end of their design process, the customer analyzed the finished product and any additional features, issues found, and missed requirements became the Customer Requirements (CR) for our project.
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Customer Rqmt. #
Description
1.1 Safe for use by children and adults1.2 Meets electrical safety standards1.3 Organize and hide wiring2.1 Assists teachers to meet curriculum (STEM learning/Common Core Standards)2.2 Active learning. Involves student in each step of the experimental growing process2.3 Team Oriented2.4 Usable by different ages2.5 Intuitive user interface (for kids)2.6 Gives user input on conditions in the seed starter3.1 Provides light source (attached to container) needed for growing plants3.2 Allows intensity/other properties of light to be comparable to that of sunlight3.3 Able to measure water, light and temperature conditions3.4 Able to record water, light and temperature conditions3.5 Able to measure amount of light provided4.1 Fits on a shelf or dresser in a home or classroom corner top4.2 Portion containing plants is portable by 3rd grader4.3 Made from sustainable materials (optional)4.4 Easy to clean4.5 Stackable (optional)4.6 Stop leak4.7 Easy to use (door)5.1 Able to grow a variety of different plant types5.2 Able to experiment with different environmental conditions (optional)5.3 Facilitates user to keep a record of data6.1 Has long life cycle6.2 Easy to repair/Low Maintenance6.3 Less expensive that the provided budget
Figure 1: Customer Requirements
In summary, the unit must be more affordable, stackable, able to fit on a standard countertop, collect and display data pertaining to soil moisture, temperature, and amount of light delivered, and be able to be integrated into either a home or classroom setting.
After these requirements were set, they were translated to engineering requirements. The engineering requirements took these vague statements and turned them into measurable requirements that would be tested at the end of the assembly process to assure that they met specification. Each requirement was given an acceptable and marginal value which defined a range in which the results could fall. The engineering requirements drove later decisions pertaining to design elements and material selection.
Source Engineering Requirement (ER) Engr. Requirement (metric) Unit of Measure Marginal Value Ideal Value Actual Value
4.1 Unit Accepts Standard Rochester Roots Seed Tray (L x W x H) Range Inches > 21x10x2 > 21x10x2 30x20x2.56.2 % Acceptance From Students and Teachers Increase Points (Max of 1,000) > 800 > 9006.2 Expected Lifetime of Unit Increase Years > 1 > 2 54.6 Time to Assemble the Unit Decrease Minutes < 120 < 60 79.375.3 Accuracy of the Temperature Reading Increase % Error < 2 < 1 0.95.3 Accuracy of the Soil Moisture Reading Increase % Error < 5 < 5 1.65.3 Accuracy of the Light Intensity Reading Increase % Error < 2 < 1 0.83.3 Sample Rate for Measuring Compartment Conditions Increase Seconds t +/- 1 t +/- 1 t +/- 0.773.5 Warm Up Time of Light Decrease Seconds < 5 < 1 0.873.2 Amount of Power Produced By the Light Range Watts > 33 50 344.2 Weight of Single, Assembled Unit Decrease Pounds < 75 < 50 64.254.1 External Dimensions of One Assembled Unit (L x W x H) Decrease Inches < 48x26x36 < 42x26x24 36x25x216.3 Cost per Unit Decrease Dollars < 1000 < 500 584.302.5 Target Age Range of Users Same Years of Age 10 81.1 Number of Stacked Units Before the System Becomes Unstable (Tipping) Same # 3 4 > 56.2 Number of Enviornmental Conditions Measured by the System Increase # 3 3 3
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After the requirements were set by the customer and then mapped to measurable quantities, it was then time to begin the design process and material selection. The first part of the unit that was considered was the frame. The frame itself was limited in size to 24” in depth (to fit on a countertop), width was determined by the size of a standard seed tray (21” by 10”), and the height was more or less left up to the design team. Multiple factors were taken into consideration when determining the final size of the unit. The depth was a hard value, but the width and height were the two dimensions that took a lot of different variables into account. The width was determined by the seed tray and the water tray it sat in. Since the seed tray is already 21” in its longest direction, mounting it from front to back would only leave 3” of room to work with, which is not enough, so it was determined to be best mounted horizontally, or the 21” length running from left to right. Since cost and ease of assembly were the driving factors, the water tray was the next item that drove the dimension. Fabricating a tray by hand to the perfect size would be expensive, time consuming, and more difficult on the supplier side to provide. So a tray was found, premade, that was 30” by 20” by 2” that fit the depth and width dimensions well. The final driver was that the seed tray would need to be inserted by hand, meaning there would have to be room for human arms to comfortably fit within the structure. Finally, the height was determined by the type of light used and how high the plants could grow in the unit, since it is only used for early germination purposes. The final exterior dimensions used were as followed: 25” depth, 36” width, and 21” height.
The next design consideration was the selection of material for construction of the frame, while considering durability, machinability, availability, and cost. After some consideration, materials were narrowed down to hardened plastic and aluminum extrusions. The plastic failed due to machinability issues and a limited amount of opportunity to add on features. The 8020 aluminum extrusion was found to be able to be machined easily at a reasonable cost, had many add-ons that allowed for capability expansion, and most importantly it is very easy for the customer to assemble themselves. The extrusions allows for every other part of the unit to be secured to it easily.
After the frame material was selected, other non-essential design features were added. The water tray needed to be supported somehow, as the units are designed for stacking. Aluminum plates that mount directly to the frame were selected based on price and weight in order to support the water and seed trays. The most important criteria was that the support plates are supported 100% by the unit and not any external mounts so that the ability to stack is preserved. Next, a manner to secure the stacked units was considered. Aluminum plates were mounted to the units, as seen in the picture below, which limits motion in each direction.
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Figure 3: CAD Final Design with Stacking
FrameThe frame subsystem makes the system appealing to the eye, structurally sound, allows for stacking, and fit
within the size requirements in addition to various other benefits. 8020 aluminum extrusion was used for our frame. Since this project is a kit consisting of parts that are handed off to a customer to build on their own, the extrusions were cut to pre-determined lengths. 8 pieces for each cut to 33”, 22”, and 17”. Each extrusion was connected by 3-way connectors in the 4 corners ultimately creating a shape of a box. The door was then precut to the specified dimensions to fit the front face of the frame. They are connected to the aluminum extrusions by hinges that bolt into the track of the extrusions. The screen was attached to the frame by using Velcro, this screen is used to protect the plants from students touching them or animals destroying the plants. The frame subsystem is then combined with the sensors and light subsystems to create our total system.
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Figure 4: Frame Subsystem Design
Features provided by the customer that we met included being able to stack, dimensions ensured to fit on a countertop, controlled lighting, and monitor and display the growing environment. The lighting, monitoring, and display features will be discussed later on. Being able to make the unit stackable was one of our top requirements. The idea to stack can allow for more units to be used. Kits can be stacked on top of each other to a maximum of 4 units. More can be done but for safety and accessibility it is not recommended. In addition to stacking on top, units can be connected side by side showing the versatility of the frame design. Building off of last year’s team design our goal this year was to make the kit fit on countertops in the classroom and at homes. The critical dimension to design around was the depth of the unit. The average countertop was 26” so our unit needed to be less than that, our outside width dimension is 25” which meets our requirement. Creating a unit that can stack and fit on countertops was crucial and our design allows the kit to do so.
Several test plans were used to validate the frame to intent. The main tests done were for tipping, external dimensions, weight of the unit, and time to assembly. Knowing the number of stacked units before the system tips was a huge safety concern and important to validate. To test this since we could not afford to physically tip and potentially damage the unit, we had to rely on calculations. From the CAD models we were able to get the center of mass for 1 through 5 units. As with all of our values, we looked at the worst case scenario so this involved the unit to be filled (water and soil), no sliding (just acts as a fixed point on the corner), and applied the force at the top perpendicular to the longest edge. To know what force the units needed to exceed before tipping we estimated it to be 142 N. This number was found by using the force generated by an 86 kg person. The person started from rest and traveled 1.91 m as fast as they could. The average time came out to be 1.52 seconds. Using the equation
d=v i t+12a t 2 and solving for acceleration of 1.65
ms2 . For force equal to mass multiplied by acceleration we were
able to find the max force the unit needed to withstand before tipping was 142.20 N. Again this is a worst case scenario because no one would be able to generate this much force unless they weighed more or was traveling faster which is not feasible in a classroom or home setting.
Number of Kits Force Needed to Tip Unit (N)1 773.512 611.723 563.624 542.305 523.61
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As you can see from the table, the kits are able to withstand the force generated of 142 N and such force will take a significant amount of force to tip. The external dimensions were validated to show that the unit would fit on a counter and be smaller than last year’s design. For our design we ended up using the following dimensions: length of 36”, width of 25”, and height of 21”. We wanted to validate that the unit could be carried and fairly light. With the kit completely filled the unit weighs 64.25 pounds, which requires two people to move the unit but with just the frame assembled one athletic person could transport it. Since our unit is a kit and needs to be assembled by a user we wanted to validate that the unit was easy and quick to assemble. By following our created assembly instructions, the kit was able to be assembled in 52:92 minutes. In order to compensate for first time users, a 50% time increase was applied to our assembly time resulting in a total recommended assembly time of 79:37, which meets our engineering requirement.
The frame subsystem was by far the most expensive part of the bill of materials (BOM). The total cost for the kit is $616.67, we were able to get some parts for free and spent $584.30. Our goal was to stay under $500 but to meet the requirements we were forced to go over in price. Our customer set a requirement to be cheaper than last year’s team of around $1000 so we were able to be within her requirement. Since the frame was our largest contributor to cost we focused on some cost reductions to lower the overall price. By buying longer pieces of extrusions and cut them down to set length we were able to save around $80. Then by researching alternatives to the pan and pan support brackets we were able to save a total of $110 on the frame subsystem.
Figure 5: Bill of Materials
LightingThe lights chosen for inclusion in the seed starter kit were 32W Blue LED Grow Lights. According to
research conducted by the team, it was discovered that blue light is the light spectrum most needed by plants in germination/seedling phase. As such, blue lights were chosen, at a power of 33W, since that was how much power was needed for the distance from the plants we had designed for.
The major challenges faced in the selection of the plants were finding lights in the desired color (blue), within the desired power range (90W from initial calculations), and within our cost budget (Less than $50). As a result of the multitude of criteria, it was hard finding a light that was suitable for inclusion in the seed starter kit. Eventually, we settled on the 32W Blue LED Grow Lights from YescomUSA, since it satisfied two criteria: Color (All Blue) and Price (~$35) but didn’t quite satisfy the power requirement. However, going by manufacturer recommendation, it was discovered that practically, 32W was enough for growing seeds, since there was also
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supplementary light (sunlight) coming in from the windows. This worked because the seed starter kits were designed to be placed by the windowsills, which will have streams of sun light coming in.
After purchasing the lights, we still needed to validate them in order to ensure that the manufacturer prescribed power was actually being produced. To validate this, a handheld light meter was used. At a specific distance, the light meter was used to measure the intensity of light outputted by the grow light in lux. Once the lux value was gotten, a formula was used to convert the lux value to watts. Since the lux value varied with distance, the specific distance used in the test was included in the equation to find the watt value (which was constant at every distance). The test was also repeated at different distances to ensure accurate values were gotten. The final watt value of the lights from the validity tests was found to be about 34.5W, which was close to the manufacturer wattage value of 32W.
After the validity of the lights was confirmed, the lights had to be attached to the kit. The lights were manufactured to be hung with a single hook from one point (like a chandelier), but the design of our frame prevented us from hanging it that way. Since we didn’t have enough space or a crossbeam to allow us hang from the top, we had to find a way to attach the lights to the sides of the frame. We achieved this by using shielded steel braded wire and s-hooks. We attached the cords to the corners of the lights and attached each cord to each of the 4 edges of the frames using hooks. This way, we were able to get the lights attached in a stable manner.
The next step was figuring out the wiring. We had a long enough wire from the manufacture so we simply ran the wire from the lights (which were hanging securely, suspended at the center of the very top of the kit) through the grooves of the frame till we got to the bottom of the kit (see Figure 2 below). The wire was connected to a programmable light timer, which we had set to turn the light on 12 hours a day (6am-6pm). The light timer was then plugged into the power source.
Figure 6: Light Wiring Diagram
Once the light was setup and connected, we were able to do testing on real plants to see how they grew under the lights. We got some seeds (thanks to Jan, Sarah and Prof. Dawn Carter). To use the lights, the light timer was simply programmed to ‘auto’ and left to run between the user input hours of 6 A.M. to 6 P.M. It could also be manually turned on or off as required. After a few weeks of growing some plants, the plants seem to be growing straight and healthy. We also grew a control group, away from the lights but in the same general area as the lights. When comparing the two, it could be seen that the plants grown under the lights were straighter, grew faster, and looked healthier. As such, it was obvious that the lights were effective.
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Figure 7: Lights Powered On and Integrated into System
SensorsIn order to create an environment for the growth of plants, the customers required the
senior design group to provide input on conditions in the seed starter. Three conditions must be provided and monitored/measured which are water, light and temperature. The foundation for the design is to be able to measure and record those three conditions. The challenge was determining the best method to display the input and having full control over the conditions to create an effective growing experiment, allowing the children to experience hands-on, and assisting teachers to meet the STEM curriculum requirement.
For the design phase, the system was separated into three subgroups to analyze each one separately and to ensure each requirement was met. The subgroups are the temperature, soil moisture and light intensity. In order to meet the customer requirement, the group has decided to use sensors incorporated with Arduino set. The sensors are temperature sensor, soil moisture sensor and light sensor. The first step is to determine the reliable and effective sensors possible to fulfill the customer requirement.
The group used the jumper wires and a mini breadboard to connect the three sensors to the Arduino. The details of the wiring process will be explained later on below. First, the DHT11 temperature sensor is placed on the mini breadboard in the Arduino case. The sensor will detect the temperature inside the seed starter container and the information will be sent to the Arduino. The Arduino then sends the reading to the display. The readings of the DHT11 sensor can be displayed either in degree Celsius (o C) or degree Fahrenheit (o F) simply by telling the Arduino using the codes. In this project, the group uses the degree Fahrenheit (o F) as a unit for the temperature measured. Secondly, the soil moisture sensor is connected to the Arduino using the mini breadboard as well and its threshold is placed inside the soil pot to measure the percentage of soil moisture. The sensor will detect the moisture of the soil and send the information to the Arduino. The readings are in range from 0 to approximately 1200, thus we converted it to percentage as it was explained above. The formula can be written in the Arduino coding. The Arduino then sends the reading to the display. The BH1750 light sensor is connected to the Arduino and placed on the aluminum frame. In order to get precise and consistent readings, it is placed at the middle of the frame. The use of this light sensor is to obviously measure the intensity of the light. This sensor was designed to measure the light intensity in lux. When it detects the light intensity, the information will be sent to the Arduino and the Arduino will send the reading to the display.
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For the temperature sensor, the group has decided to use DHT11 temperature sensor because of its low cost and small size. It is a digital sensor that lets you easily receive relative temperature and humidity readings in your project. This sensor obviously is used to measure temperature of the surrounding air. It is fairly simple to use, but requires careful timing to get the data. The component is 4-pin single row pin package with 0.1” spacing and it is easily and convenient to use with Arduino. This sensor can be powered from 3.0 to 5.0V and uses 2.5mA maximum current during conversion (while requesting data). Besides that, the DHT11 sensor is good for 0-50oC temperature reading with ±2oC accuracy.
Soil moisture sensor:For the soil moisture sensor, the group has decided to use Sunkee Soil Hygrometer detection module soil
moisture sensor. This is because it is a simple water sensor and can be used to detect soil moisture. It is equipped with a potentiometer and has soil moisture thresholds that can be used in module plant waterer device and the plants in your garden under soil humidity control. This sensor also can improve performance of conduction, prevent contact with the soil from rust problem and prolong life. With operating voltage of 3.3V to 5.0V, it is a perfect soil moisture sensor than can be used in this project incorporated with the Arduino set. In addition, this sensor can produce dual output mode, however analog output can give a more accurate reading. This sensor will provide reading in range from 0 to approximately 1200 and in order to give a meaningful output to the customer, the group created a formula to convert the reading to percentage (%). It will be explained later on.
Light Sensor:For the light sensor, the group has decided to choose BH1750FVI Digital Light Intensity
sensor for this seed starter project. It is a digital ambient light sensor IC for I2C bus interface. This IC is the most suitable sensor to obtain the intensity of light data for adjusting LCD and perfectly compatible with Arduino. It is possible to detect wide range at high resolution. This sensor can be powered with a minimum Vcc voltage of 2.5V and maximum of 3.6V. It can detect light intensity from 0 lux up to 65535 lux and its accuracy is about 1.2 times in average.
Figure 8: Temperature sensor, Soil Moisture sensor, and Light Intensity sensor
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Figure 9: Arduino, breadboard, sensors, and display wiring diagram
DisplayFor this project, the group decided to use a Sainsmart 1.8” TFT LCD Display to display
the readings from the sensors. It is an LCD display with 128x160 color pixels and a SPI interface that is transmissive and normally white. It is also 256K colors and has a small compartment to place a microSD card holder so the users can easily load full color bitmaps from a FAT16/FAT32 formatted microSD card. The screen includes a controller ST7735R which can display full 18-bit color (262,144 shades). This LCD display is chosen because it is compatible with 3.3V/5V Arduino and can it is easy to use. The TFT LCD Screen can display information from the Arduino. Based on the customer requirement, the Arduino is coded to display the sensors readings. The three readings that will be displayed by the LCD are temperature (oF), soil moisture (%) and light intensity (Lux). In addition, the great part of the LCD is that it has a built microSD socket, so the users can store data of the readings for the seed starter project. Picture 1 below shows the display of the data from the sensors.
Figure 10: Display Screen
Arduino CodingThe Arduino coding basically tells the Arduino what to do and the Arduino will send
the information to the LCD display to display what it was told to show. At the beginning of
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the coding, the users need to declare the function that they want to use. Each sensor has a specific coding for Arduino. The users can find codes from some websites and copy and paste the code in the Arduino IDE, upload and run it. However, it can only read a specific sensor. Since in this project, the group uses three different sensors, we need to find three different codes and combine them into one program. In order to create coding overall coding for those three sensors, the users need to understand line by line of the code.
Results and discussionThe key findings of our project were researching and validating our lighting source. Selecting a light that
was within our price range and yet still produced the needed energy and wavelength to grow seeds efficiently. The light cost around $50 which is well within what we expected to pay while also meeting all our needs of desired power output, color of the light, wavelength, and little to no amount of heat produced by lights. The LED grow lights actually exceed our expectations and grew the plants more efficiently than what we expected. Also it covers a wide range that even exceeds the base of our frame.
All of our test results validate that our design was a success and met the customer and engineering requirements. Not all our tests met the ideal value that we hoped for our results but they met the marginal value which is still acceptable by the team and our customer. Along the way our team faced some challenges but luckily we were able to work together and overcome them. Our first major issue that we encountered was validating each subsystem and verifying that they work to intent. We had concerns about if the lights, sensors, and display would actually work and work together. Once we validated them and were satisfied with the results then it was time to see if they worked as a complete system. We knew the sensors worked and the displayed work but could the display actually show the accurate readings of the sensors. We did not have too many issues bringing each subsystem into one. By following through our test plans it was validated that the system works as expected. Another challenge was the cost of the system. Trying to keep costs down while still meeting all of our customer needs was a very challenging task. Unfortunately we were unable to stay under the project cost of $500 but were able to stay under our customer cost of $1000. Our plan was to design to meet our full range of requirements and then brainstorm ideas to cut costs. This was very effective because we did not use any parts that were cheap and could potentially effect the overall appearance or performance of the kit.
As a group we experienced many success as can ultimately be seen by the final project that was delivered. Our biggest success was our ability to meet all of our customer requirements and deliver a satisfying project. To be able to have a system that can have its own attached seed grow light, monitor, record, and display the growing conditions is something that was a huge success. Also to be able to deliver a product that can fit on counter tops in the classroom and at home and that is stackable speaks to the versatility to our design as well. This product can be used in many different ways and easy additions can be made as well for specific customer needs.
Conclusions and recommendationsUltimately our project met our intent to control lighting, monitor and display plant growth, be stackable,
and fit on countertops. As with everything there is always room to grow and improve. Some ideas that could be used in the future for advancements are to have attachments to make it useable outdoors, have add on features for the customer, and have various sizes for the frame so someone who wants to use it on the floor and has more room can grow more seeds at once. Also another advancement could be to make a plant growing kit. Our kit is only used to start seeds and then transfer the plants to the garden. Ideally it would be nice to give the option for the system to grow full plants. Based off of our current design some improvements that could be made are decreasing the overall cost to make it more affordable for parents at home and teachers in the classrooms. It would also be good to improve the screen attachment design. It works to intent but could be improved, the reason why we went with the Velcro is for cost reasons. One could use stronger Velcro or another attachment method such as magnets or inserts into the aluminum extrusion tracks. Our project was a huge success, we were able to deliver a successful product to our customer, and meet all of our engineering requirements and goals. The rewarding thing about this project was that we delivered a product that can help students learn about agriculture and plant life.
References ● None
Acknowledgements ● Rochester Roots and Montessori School
