This is my first robot which is very simple line follower. I,Anil K M,J Rajasekhar Reddy made it for out college technical festival. Later I made two other line followers using microcontrollers but I don't have the programms of it.




Working Principle:Here we used the black strip of thickness 3cm. We made the track by combining four white sheets together and pasting black strip over it. In this we are designed the robot in such a way that when black strip comes under the LDR (means the robot try to cross over the black strip) the correspond motor will become off. This happens when curved portions comes. So the other motor works and robot will take the turn.

Here the LDR resistance varies from 400ohm to 200Kohm. When robot is in White strip:
When the robot in white strip the resistance of LDR is in the range of 400ohm- 5K ohm. So the voltage V1,
V1= 50/(50+LDR)*V
V1-voltage at the base of transistor
LDR- resistance of LDR
V-supply voltage
So adjust 50Kohm variable in such a way the V1>.8V so that transistor is in saturation.

When transistor is in saturation,
so the current Ic=Ie becomes
Ic=(V-.2)/(1+1+5.6) mA
so the voltage drop at the emitter Ve=(V-.2)*(1/(1+1+5.6)
Ve must be greater than .8V so that KSD880 become saturate.
voltage drop

V2= (V - .2)*((1+5.6)/(1+5.6+1) V
so Vbe for 2N6107 becomes
Vbe= V - V2
This Vbe must be greater than .8V so that 2N6107 will saturate. In the case of 2N6107 it is a P N P transistor So in the connection we can see that Emitter is connected to Vcc.
Base is connected in such a way that Transistor E-B junction is forward biased.
Thus both transistor both will conduct and the motor will rotate.
When robot is in black strip:
In this case the LDR resistance is in range of 100Kohm-200Kohm. Thus V1 become less than .8V so that BC548 will not saturate and no current flows through the collector
and emitter terminals. So the voltage drop
Thus both transistor are cut off so the motor is in high impedance state. In this condition all transistors are cut off. Adjust 50K variable resistor in order to satisfy both conditions.

motor : 12V / 250 mA
This motor is a geared one so that speed is slow.
This motor will work on 3V( which one I used).
LDR: 400ohm - 200Kohm
cost- Rs.6
battery (2*1.5V)



Here main limitation comes on reaction time of LDR

The LDR used are very cheap so their reaction time was very slow

matching between Inertia and reaction time of LDR

If we use some good speed the robot will cross the black strip

because of reaction time of LDR and due to inertia. So the speed

should be kept optimum.

Proper lighting:

We are keepind LDR's on the bottom of the robot so the proper

lighting should be provided. Lighting should be of high intensity.

Then we get better response. We used two 2.5V bulbs. It is better to

use flourescent lamps.In black strip reflection is less.

Here you can see that the robot is going forward and taking turn.

So this should be avoid by fitting LDR in the front so that the robot

will take turn as a normal vehicle take turn.