INDEX

LIGHT FOLLOWER ROBOT
The aim of light follower is to follow light. So LDR can be used for good response because we are using visible light. So I assume that you are having a robot having two motors. We start with two LDR sensors assuming that you are applying light from front.

Here I am just showing an overview of the robot. So let's try to make one using LDR,comparator and some transistor or L293D.

Here is a simple block diagram. Here first part is an LDR circuit which senses the light. LDR circuit is having one series resistor with LDR and output taken across LDR. The the output of two LDR's is applied to a difference amplifier. Difference amplifier is a subtractor with some amplification. The output of the amplifier is having some gain. This output is applied to a motor driving circuit. The first one is using PNP transistor with its motor in collector. The second one is NPN transistor motor. This complementary transistors are used because the output of the difference amplifier is +ve or -ve. If +ve NPN transistor will become and active and motor connected to the collector of that NPN transistor will work, while the PNP transistor is OFF and motor in collector of motor is OFF. If -ve
PNP transistor is saturated and motor connected to collector of PNP will run while that of NPN which is cut off will not run.

This circuit is a closed circuit, but this circuit is not stable because there is no condition exist the motor will stop. You can see that the output of the difference amplifier will be +ve or -ve at any time. Both motors will stop when voltage is in range of +.5v and -.5V. Because in this range both motor will be cut off. But remember the factor of inertia. So when the motor is just to stop due to inertia it moves some distance, this makes a small difference in the LDR reading and this reading will be get amplified and motor will start rotating again.