Accelerometer Controlled Robot without a Microcontroller

You may have come across many tutorials about accelerometer controlled wireless robot (also known as gesture controlled or glove controlled) but all of them would have a microcontroller. This tutorial teaches you how to make them without using any microcontroller.

Fig. 1: Prototype of Microcontroller Less Accelerometer Controlled Robotic Car

Image: Final Image of Accelerometer Controlled Robot

Components required:

1. Dual axis Accelerometer

2. 4x 10k potentiometer

3. LM324 OP-AMP IC

4. HT12E+HT12D encoder decoder pair

5. ASK RF Transmitter and Receiver pair

6. L293D Motor Driver IC

7. 2x DC motors

8. 2x wheels

9. Castor wheel

10.Chassis

11.Breadboards

12.Wires

Block Diagram:

Fig. 2: Block Diagram of Microcontroller Less Accelerometer Controlled Robotic Car

Accelerometer

As the name says, accelerometers are sensors used to sense the proper acceleration in a given axis.

The one I am using is a MMA7361L three-axis accelerometer module (i.e. x, y and z) however we will be using only two axes (x and y).

Fig. 3: Image showing MMA7361L Accelerometer Module

These sensors give analog output proportional to the tilt angle or orientation. We’ll discuss about this later.

LM324 Op-Amp

LM324 consists of four operational amplifiers which we would use as comparators. One of the inputs of each op-amp would be connected to the accelerometer’s output. And other inputs would be connected to their respective potentiometers which would be tuned later to give the required digital output.

We need four different combinations (For Forward, backward, right and left).

Imagine your hand as the accelerometer. The direction your fingers point to is the positive Y direction and opposite to it is the negative Y. Perpendicular to your fingers, X axis exists.

Fig. 4: Image showing Accelerometer Axis’s on a plane with reference to hand

Fig. 5: Image showing Accelerometer Axis’s in three dimensions with reference to hand

These are the four orientations we would be assigning:

Fig. 6: Image showing Accelerometer Orientations by hand for navigating robot

Now at normal position (accelerometer parallel to ground), the X and Y outputs of the sensors gives a fixed analog voltage. Read it using a multi-meter. Below are the values I got from my sensor when in normal position and then after tilting the sensor as shown in the diagram above.

VOLTAGE READING	TILT DIRECTION
(in Volts)	NO TILT	FORWARD	BACKWARD	RIGHT	LEFT
X	1.65	NA	NA	2.3	1.1
Y	1.65	2.2	1.1	NA	NA

Now depending on these voltage values, we need to tune the potentiometers to get the correct digital output. Consider the following diagram

Fig. 7: Circuit Diagram of MMA7361L Accelerometer and LM324 based circuitry for sensing analog voltage for X axis

Now depending on these voltage values, we need to tune the potentiometers to get the correct digital output. Consider the following diagram Here Vx is the analog voltage coming from the X output; V1 and V2 are output voltages of the potentiometers. Remember V2 > V1. The circuit follows the below table:

Conditions	Output 1	Output 2
Vx > V2	LOW	HIGH
Vx < V1	HIGH	LOW
V2>Vx>V1	LOW	LOW

So we need to adjust V1, V2 values (using the potentiometer) based on the reading we got and the above table.

You can see a demonstration in the video at the end. I connected LEDs to the output pins to see its state.

Similarly we do this for Y output also.

Then we would get the below 4-bit output from the LM324 IC:

Tilt Direction	O1	O2	O3	O4
FORWARD	1	0	0	0
BACKWARD	0	1	0	0
RIGHT	0	0	1	0
LEFT	0	0	0	1

For Encoder/Decoder and RF ASK transmitter/Receiver, refer to this tutorial: http://www.engineersgarage.com/electronic-circuits/dc-motor-control-circuit-wireless-rf

Motor Driver

We will be using L293D motor driver which can control two motors bi-directionally. The reason we use a motor driver is because circuits (most of them)/ microcontroller work at a different voltage level when compared to the motor and they cannot provide enough current to the motors. L293D has 4 inputs and 4 output terminals. Here is a table showing the input combinations and corresponding outputs.

INPUTS				MOTOR DIRECTION		ROBOT’S MOTION
I1	I2	I3	I4	LEFT MOTOR	RIGHT MOTOR
1	0	0	1	ANTI CLOCKWISE	CLOCKWISE	FORWARD
0	1	1	0	CLOCKWISE	ANTI CLOCKWISE	BACKWARD
1	0	1	0	ANTI CLOCKWISE	ANTI CLOCKWISE	RIGHT
0	1	0	1	CLOCKWISE	CLOCKWISE	LEFT

Why was a microcontroller needed?

Well if you carefully compare the output table of LM324 IC and the Input table for Motor driver, you would notice a problem.

COMPARATOR OUTPUT				MOTOR DRIVER INPUT				DIRECTION
O1	O2	O3	O4	I1	I2	I3	I4
1	0	0	0	1	0	0	1	FORWARD
0	1	0	0	0	1	1	0	BACKWARD
0	0	1	0	1	0	1	0	RIGHT
0	0	0	1	0	1	0	1	LEFT

Out of 4bits coming from the comparator, only one is high at a time whereas for motor driver, to drive the motors correctly requires two bits to be high and that too in a particular order. That’s where the microcontroller comes into play. We program it in such a way that it takes in the output from the comparator and gives out the correct sequence to the motor driver. Like this:

If (input==1000) output=1001;

Else if (input==0100) output=0110;

Else if (input==0010) output=1010;

Else if (input==0001) output=0101;

How I eliminated the microcontroller?

For this, I simply used an extra IC in place of the microcontroller i.e. a quad 2-input or gate IC. Yeah I am serious, that’s the only extra thing I used. Don’t believe me? Then look at the diagram below. Tally the values of above table with the diagram and equations.

Fig. 8: Circuit Diagram of Digital Gates used in place of Microcontroller to control movement of Robotic Car

At Gate A, I1 = O1 + O3

Gate B, I2 = O2 + O4

Gate C, I3 = O3 + O2

Gate D, I4 = O4 + O1

Quite simple isn’t it?

Now that we are done with our designing, let’s move on to the next part.

Hardware Setup:

Gather all the parts shown in the image.

Fig. 9: Image of Components required for making Robotic Car

Attach the motors to the chassis and then the wheels to the axle.

Fig. 10: Image showing DC Motor attached Metallic Frame of the Robot’s Body

Fig. 11: Image showing wheel attached to DC motor on Robotic Car

Use some screws and bolts to attach the castor wheel

Fig. 12: Image showing Caster Wheel attached on Front Side of the Robotic Car

Arrange the transmitter and receiver circuit as per the circuit diagram.

Connect the motors to the motor driver output, and power both the transmitter and receiver. That’s it! You are ready to go!

Fig. 13: Image showing Frame of Robotic Car fully assembled with DC Motors and Wheels

Arrange the transmitter and receiver circuit as per the circuit diagram.

Fig. 14: Prototypes of Transmitter and Receiver Circuits for Robotic Car designed on Breadboards

Connect the motors to the motor driver output, and power both the transmitter and receiver. That’s it! You are ready to go!

Fig. 15: Prototypes of Receiver Circuit attached to Robotic Car

Circuit Diagrams

Circuit-Diagram-RF-Transmitter-Designed-Accelerometer-Controlled-Microcontroller-Less-Robotic-Car
Circuit-Diagram-RF-Receiver-Designed-Accelerometer-Controlled-Microcontroller-Less-Robotic-Car