Monday, July 19, 2010

To make a robot which can follow a white strip on black background and can extinguish fire on its way .

line follower robot
Design Specifications 
1. For proper functioning of the robot needs a voltage supply of about 5.3V and current about 0.7A.
2. The robot should be able to distinguish between the white and the black surface.
3. If the black surface suddenly ends, the robot should keep on moving in the direction it last moved
   until the black line is again there.
4. It should stop and extinguish fire and restart only after making sure that the fire has been 
5. This could not be run using the dry cells because of the current requirement.

                   The basic principle used is the difference in reflection of light from a white surface 
and a dark surface .This could be sensed using two LDR's. The two inputs would be fed to two different 
comparator whose comparing voltage is set using the potentiometer .When the light is reflected by the black 
surface the resistance of  LDR is high, hence the voltage is high and vice versa .The current flowing through
the output of comparator is very low to drive the motor .Thus ,a Darlington pair is applied to the output of 
the op-amp .This output could be used to run the H-bridge circuit which can rotate the motors in both the 
directions. It would continue moving in the line it was last moving if there is no line.It can navigate through
almost all turns.
        If a flame comes in the way the third LDR mounted on the top will detect it and stop the motors of tyres
and startthe fan. When the fire extinguishes,fan stops and the motor starts again and it continues in same 

Working of the Robot

The circuit implemented consists mainly of two different sub-circuits.
          The first part comprises of making the robot follow a black strip. This was done using a comparator 
circuit using the LDR whose reference voltage was fixed using the potentiometer. This was based on the 
phenomenon that the resistance of the LDR decreases as the intensity of light falling on it increases. In our 
case, the light reflected from the white surface is more than that from the black surface. Therefore, the 
voltage in positive terminal of the comparator remains high as long as the robot is moving on white surface. 
If the black surface come under one of the two LDR.s the motor corresponding to that LDR stops, the other making 
it move away from the black line. But as the other LDR crosses the black line, its motor stops, the other 
forcing it in other direction, resulting in its following the black line. Thus ,the output voltage of the Op-Amp 
has been varied according to the need,but the current flowing through the output of Op-Amp is in some mA .Thus 
there was need for current amplification. The Darlington .pair was used for the same. The resistance of the motor 
was 5-10ohms,thus source follower circuit was used.
  The second part comprised of using LDR.s and IR-receivers to detect flame .The dual Op-Amp LM358 
was used for the same. The two comparator circuits were used .For LDR, the working was same, but for IR receiver 
the voltage and not the resistance vary according to the intensity of light. Thus the two ends of IR-receiver 
were connected to ground and positive terminal of the comparator .The output of these two were ORed and given to 
a monostable 555 timer with time period of 4 sec.555 was used because when the robot sees the fire ,the fan 
starts and the motors stop but when fan starts the intensity of light decreases and hence the two motors start 
again and there is a chance that the motor starts before the fire is extinguished .The 555 helps in generating a 
high pulse of about 4 seconds which will remain high and will not depend on the intensity of light for the same 
duration .Thus , this will make sure that the fire is extinguished before moving ahead. Once the fire is 
extinguished it will retain its original motion.   

1. The robot can be used as a guider to guide the visitors from the entrance to the main office .
2. It can help doctors to carry the medicines from one ward to another .
3. The main purpose is to rescue the people by extinguishing fire in a building .

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