Light Following Robot

The main purpose of this project is to design a robot which would follow the path of higher luminescence across all directions.It is based on the principle that resistance of a LDR changes with the amount of light falling on it.

It consists of 3 modules

Sensor Circuit

It consists of 4 LDRs' arranged at each side of the robot (front, back, left, right). The resistance of an LDR will decrease with the increase in the luminescence. This variation is fed to a comparator with a reference voltage set. We use LM324 IC which conveniently has 4 comparators on a single chip. In our case we found that each LDR was having different response the same luminescence. For example, for the same indoor daylight the LDR resistances were respectively 6k, 8k, 9k, 10k. To offset this variation, we are using seperate pot for reference voltage for each LDR. You can use a single pot and use the same reference voltage for all 4 LDR's if you find that LDR's are having the same response (i.e shorting pins 3,5,10,12 in LM324). The 4 outputs of comparator is fed to a port of Microcontroller 8051 via port P0.

Microcontroller

The microntroller used here is 89c51. The microcontroller gets the sensor inputs via port P0. The micrcontroller will drive the robot only when one of the LDR's resistance (i.e one of front, back, left, right) is below the threshold and consequently the output of the comparator is logic HIGH. The microcontroller will send the signal for the robot to drive in specific direction via port P1. One thing to note is that the robot can move either forward or backward. In case it moves forward and then right, the robot turns right looking into forward direction. Similarly, if the robot moves in the opposite direction i.e reverse and then right, the robot needs to move right looking into reverse direction (or left looking into forward direction).

DC motors with H-Bridge

The DC motor driver or H-bridge IC used here is L293D. The H-bridge converts the logic voltage 5v into DC motor specific 9v and also takes care of back emf when the DC motor direction reverses. The microcontroller send the signals to H-bridge via P1 based on which the robot moves in the specific direction (or stops). The DC motors used here is 150RPM, considering that there is not much load, higher RPM motors can be used to get higher speed.