AIM: The primary aim of the project is to learn about interfacing external peripherals such as sensors and motors, to a microcontroller and program it to behave in an expected manner, based on the information collected. This is done by designing a wall following robot which collects information from its IR sensors and outputs information to the motors which drive the robot. The main task of the robot is to move parallel to a wall and at the same time avoid any kind of collision with the wall. It is however necessary to design some interfacing circuits to drive the motors and to receive data from the sensors in a way that the microcontroller would understand.

Project Description

The project may be divided into three main parts. Each of these parts will then be explained in detail.

1. Robot Hardware (Body)

2. Interface Circuitry

3. Algorithm/Program

Robot Hardware:

The robot’s body was constructed using two hard plastic sheets which were cut into circular plates. The two plates where then mounted on top of each other using stand-off’s, creating gap in between them, which was used to mount the battery. Two motors with gear box were used to drive the robot using a differential wheel arrangement. The wheels were mounted on the gear box and then entire assembly was fixed on the lower plate.

The HCS12 evaluation board was mounted on the top plate and all circuits were designed on the prototype board provided along with the evaluation board. Three sensors were mounted on the right hand side of the top plate, which would help in following the right wall and one sensor was mounted in the front to detect a wall in the front.

A picture of the robot is shown in Fig 1.

2. Interface Circuitry:

The interface circuitry was required in order to control high current hardware (such as motor) using the microcontroller and to understand the signals given out by the IR sensor. The two main circuits used are,

a. Motor Driver Circuit

b. IR Sensor Circuit

Result and Conclusion

The robot worked as expected. It completed the maze fully and detected U turn and front walls perfectly. However, there were many difficulties that came across during the course of the project. One of them was driving the motors. Whenever the motor dragged more current under higher load, it would reset the evaluation board as the drop out voltage of the regulator was too close to the output voltage. In this case the board would automatically reset itself. In order to overcome this problem, the voltage to the motors was controlled using the adjustable voltage regulator, in such a way that at maximum load, the motor drops out the voltage of the board’s supply, just enough to keep it at 5V mark. This would not reset the evaluation board. Another problem was sensitivity of the IR sensors. The output voltage from the IR sensor circuit was first derived from the emitter of the photo transistor. However, it was found that the voltage range would be from 3 to 5 volts. This was because the impedance of the analog port along with the impedance of the photo-transistor, forced the voltage range to be limited. However, if the voltage was derived from the collector, a full range from 0 to 5 volts was attained.