Hand gesture controlled wireless robot using accelerometer

Introduction:

An accelerometer is a device that measures proper acceleration, also called the four-

acceleration. For example, an accelerometer on a rocket accelerating through space will measure

the rate of change of the velocity of the rocket relative to any inertial frame of reference. However,

the proper acceleration measured by an accelerometer is not necessarily the coordinate

acceleration (rate of change of velocity). Instead, it is the acceleration associated with the

phenomenon of weight experienced by any test mass at rest in the frame of reference of the

accelerometer device. An accelerometer thus measures weight per unit of (test) mass, a

quantity of with dimensions of acceleration that is sometimes known as specific force, or g-

force (although it is not a force). Another way of stating this is that by measuring weight, an

accelerometer measures the acceleration of the free-fall reference frame (inertial reference

frame) relative to itself (the accelerometer). This measurable acceleration is not the ordinary

acceleration of Newton (in three dimensions), but rather four-acceleration, which is acceleration

away from a geodesic path in four-dimensional space-time. Single- and multi-axis models of

accelerometer are available to detect magnitude and direction of the proper acceleration (or g-

force), as a vector quantity, and can be used to sense orientation (because direction of weight

changes), coordinate acceleration (so long as it produces g-force or a change in g-force),

vibration, shock, and falling (a case where the proper acceleration changes, since it tends toward

zero). Micro machined accelerometers are increasingly present in portable electronic devices

and video game controllers, to detect the position of the device or provide for game input. An

accelerometer at rest relative to the Earth's surface will indicate approximately 1 g upwards,

because any point on the Earth's surface is accelerating upwards relative to the local inertial

frame (the frame of a freely falling object near the surface). To obtain the acceleration due to

motion with respect to the Earth, this "gravity offset" must be subtracted and corrections for

effects caused by the Earth's rotation relative to the inertial frame.

Conceptually, an accelerometer behaves as a damped mass on a spring. When the accelerometer experiences an acceleration, the mass is displaced to the point that the spring is able to accelerate the mass at the same rate as the casing. The displacement is then measured to give the acceleration.

Accelerometers are very important in the sensor world because they can sense such a

wide range of motion. They're used in the latest Apple PowerBooks (and other laptops) to

detect when the computer's suddenly moved or tipped, so the hard drive can be locked up

during movement. They're used in cameras, to control image stabilization functions.

They're used in pedometers, gait meters, and other exercise and physical therapy devices.

They're used in gaming controls to generate tilt data. They're used in automobiles, to

control airbag release when there's a sudden stop. There are countless other applications

for them.

Possible uses for accelerometers in robotics: 

Self balancing robots

Tilt-mode game controllers

Model airplane auto pilot

Alarm systems

Collision detection

Human motion monitoring

G-Force Detectors

As our final year project we are going to present an innovative robot based on

Accelerometers. In

This project we have two parts, Transmitter and receiver circuit. In transmitter circuit we

are using accelerometer to sense hand gesture, microcontroller to process the data and

FSK transmitter to transmit the data to the Receiver (Robot)

In receiver circuit we have FSK receiver, microcontroller and H-bridge Dc motor driver.

The received data is processed by the microcontroller for the specific movement and H-

bridge DC motor drive actuates this data.

Block diagram:

Analog to digital converter

PIC Microcontroller

Accelerometer

433 MHZ Transmitter

HT12E Encoder

Block diagram:

HT12D Decoder

PIC MicrocontrollerObstacle

Detector

433MHZ Receiver

DC motor

H-bridge driver

Light sensor

Circuit diagram:

Robotics develop man-made mechanical devices that can move by themselves, whose

motion must be modeled, planned, sensed, actuated and controlled, and whose motion

behavior can be influenced by “programming”. Robots are called “intelligent” if they

succeed in moving in safe interaction with an unstructured environment, while

autonomously achieving their specified tasks.

This definition implies that a device can only be called a “robot” if it contains a

movable mechanism, influenced by sensing, planning, and actuation and control

components

Robotics is, to a very large extent, all about system integration, achieving a task by an

actuated mechanical device, via an “intelligent” integration of components, many of

which it shares with other domains, such as systems and control, computer science,

character animation, machine design, computer vision, artificial intelligence, cognitive

science, biomechanics, etc. In addition, the boundaries of robotics cannot be clearly

defined, since also its “core” ideas, concepts and algorithms are being applied in an

ever increasing number of “external” applications, and, vice versa, core technology

from other domains (vision, biology, cognitive science or biomechanics, for example)

are becoming crucial components in more and more modern robotic systems.

Research in engineering robotics follows the bottom-up approach: existing and

working systems are extended and made more versatile. Research in artificial

intelligence robotics is top-down: assuming that a set of low-level primitives is

available, how could one apply them in order to increase the “intelligence” of a

system. The border between both approaches shifts continuously, as more and more

“intelligence” is cast into algorithmic, system-theoretic form. For example, the

response of a robot to sensor input was considered “intelligent behavior” in the late

seventies and even early eighties. Hence, it belonged to A.I. Later it was shown that

many sensor-based tasks such as surface following or visual tracking could be

formulated as control problems with algorithmic solutions. From then on, they did not

belong to A.I. any more

Axis of Acceleration 

The tiny micro-structures can only measure force in a single direction, or axis of

acceleration. This means with a single axis measured, you can only know the force in

either X, Y, or Z directions, but not all. So if say your X-axis accelerometer endowed

robot was running around and ran into a wall (in the X direction). Your robot could detect

this collision. But if say another robot rammed into it from the side (the Y direction),

your robot would be oblivious to it. There are many other situations where a single axis

would not be enough. It is always a good idea to have at least 2 axes (more than one

axis).

Gravity 

Gravity is an acceleration. As Such, your accelerometer will always be subject to a -9.81

m/s^2 acceleration (negative means towards the ground). Because of this, your robot can

detect what angle it is in respect to gravity. If your robot is a biped, and you want it to

always remain balanced and standing up, just simply use a 2-axis accelerometer. As long

as the X and Y axes detect zero acceleration, this means your robot device is perfectly

level and balanced.

Accelerometers Rated G 

When you buy your accelerometer, you will notice it saying something like 'rated at 2g'

or '3g accelerometer.' This is the maximum g force your sensor can report. Gravity

accelerates objects at 1g, or 9.81 m/s^2. For example, if your robot is moving at 1g

upwards, then that means you sensor will detect 2g. For most robotics applications a 2g

rating will be fine. So why not just get the highest rating possible? The lower the rating,

the more sensitive it will be to changes in motion. You will always have a more fine

tuned sensor the lower the rating. But then again, more sensitive sensors are more

affected by vibration interference.

Calculate Acceleration and Angle with respect to Gravity 

To calculate the magnitude of acceleration for a 

single-axis accelerometer

acceleration_max = sqrt(x^2) = x

2-axis accelerometer

acceleration_max = sqrt(x^2+y^2)

3-axis accelerometer

acceleration_max = sqrt(x^2+y^2+z^2)

To calculate the detected force on an accelerometer due to gravity: 

Force_gravity = -g*cos(angle) (depends on starting axis of sensor)

Chances are you would have no need to measure the force, but if you reverse the equation

you can calculate the angle by knowing the detected force: 

cos(sensor_value*conversion_constant / -g)^-1 = angle

HT12E Decoder

18 PIN DIP, Operating Voltage : 2.4V ~ 12.0V Low Power and High Noise Immunity, CMOS Technology Low Stand by Current, Ternary address setting Capable of Decoding 12 bits of Information 8 ~ 12 Address Pins and 0 ~ 4 Data Pins Received Data are checked 2 times, Built in Oscillator needs only 5% resistor VT goes high during a valid transmission Easy Interface with an RF of IR transmission medium Minimal External Components

Transmitter:

For controlling robot we have used RF transmitting remote. For Rf transmission we have

used HT12E Decoder IC. The 212 encoders are a series of CMOS LSIs for remote

control system applications. They are capable of encoding information which consists of

N address bits and 12_N data bits. Each address/ data input can be set to one of the two

logic states. The programmed addresses/data are transmitted together with the header bits

via an RF or an infrared transmission medium upon receipt of a trigger signal. The

capability to select a TE trigger on the HT12E or a DATA trigger on the HT12A further

enhances the application flexibility of the 212 series of encoders. The HT12A

additionally provides a 38kHz carrier for infrared systems.

          For the proper working of this local control section a permanent 5V back up

needed continuously. This is achieved by using a 230V to 12V transformer, Bridge

rectifier, capacitor filter and 5V regulated power supply from a voltage regulated IC

7805. This 5V source is connected to all ICs and relays.

RF Receiver: For RF transmission purposed it is needed to encode the signal generated

at computer parallel port with the help visual basic code. For signal encoding purpose we

have used HT 12E encoder. HT^12 E is 2^12 encoders are a series of CMOS LSIs for

remote control system applications. They are capable of encoding information which

consists of N address bits and 12_N data bits. Each address/ data input can be set to one

of the two logic states. The programmed addresses/data are transmitted together with the

header bits via an RF transmission medium upon receipt of a trigger signal. The

capability to select a TE trigger on the HT12E enhances the application Flexibility of the

2^12 series of encoders.

Encoder

18 PIN DIP Operating Voltage : 2.4V ~ 12V Low Power and High Noise Immunity CMOS Technology Low Standby Current and Minimum Transmission Word Built-in Oscillator needs only 5% Resistor Easy Interface with and RF or an Infrared transmission medium Minimal External Components

Obstacle sensor:

The infrared intruder sensor is used to sense some unknown person like thief entering in

your house without your permission.

In the infrared sensor we use IC 555 as a main component. Pin no 4 and pin no 8 is

connected to the positive supply. Pin no 1 is connected to the negative voltage. One

capacitor is grounded from the pin no 5 for noise cancellation. Output is available on the

pin no 3. Sensor is connected to the pin no 2.

In the case of infra red sensor Pin no 2 is negative bias through the 33k ohm resistor and

pin no is positively biased through the photodiode. One infrared transmitter led is focused

to the photodiode. Infra red led is directly connected to the positive and negative supply

through the 330ohm resistor.

In normal stage when light is focusing on the photodiode then pin no 2 is positively

biased photodiode. If pin no 2 is positive then negative output is available on the pin no

3. Now when any body interrupts the light then there is no light on the photodiode and

pin no 2 is now gets its voltage from only 33 k ohm resistor. If pin no 2 is become

negative then output is shifted to the pin no 3. When positive output is available on the

pin no 3 and with the help of this voltage NPN transistor is on and npn transistor provide

a negative voltage as a pulse to the microcontroller (pin No 33, 34, 35, 36)

Light sensor: An LDR is used to sense light. The output voltage of a LRD is amplified

by an operational amplifier, and is inputted into the base of transistor .The temperature

sensitivity adjusting the gain of an operational amplifier by VR.

So in the normal mode when temperature is below 60C the output or LM358 is not

sufficient to drive transistor BC 548. When temperature raises above 60C the output of

LM358 is about 3V which is sufficient to drive transistor thus microcontroller get

positive voltage.

DC motor driver: The H-Bridge is used for motor driver. The H-Bridge is widely used

in Robotics for driving DC motor in both clockwise and anticlockwise. As shown in the

circuit diagram in H Bridge two NPN and two PNP transistors is used.

Let us consider microcontroller provide high at pin No 13 and low at Pin No 14 thus

right side NPN transistor conducts and left side PNP transistor conducts. This means M12

is 12v and M11 is grounded thus motor rotate clockwise

Again let us consider microcontroller provide low at pin No 13 and high at Pin No 14

thus right side PNP transistor conducts and left side NPN transistor conducts. this means

M12 is grounded and M11 is 12v thus motor rotate anticlockwise.

Frequency of 433MHz is used in low power devices. 433 MHz radios are short range,

licence free communication devices authorized for use in many parts of the world. In

some countries, however, voice is not allowed over LPD. They operate in the UHF band

from 433.075 MHz to 434.775 MHz with 25 kHz channel spacing, for a total of 69

channels. These devices are frequency modulated(FM) with a maximum legal power

output of 10 mW. LPD devices must only be used with the integral and non-

removable antenna. LPD was introduced to reduce the burden on the channels over

shorter ranges (less than 1 km).