Post has attachment
Line follower is an autonomous robot which follows either black line in white are or white line in black area. Robot must be able to detect particular line and keep following it.

 For special situations such as cross overs where robot can have more than one path which can be followed, predefined path must be followed by the robot.

In the following section, we will discuss the line follower robot which follows black line in white area and take right turn whenever cross overs or Y shaped turn arrives.

However with some minor suitable changes, users can make robot for other possibilities also

An array of sensor is used to detect the line. Based on the status of sensors, special circuit or controller decides the position of line and also the required direction of motion required to follow the line. Motor driver circuit is used to ON/OFF the LEFT/RIGHT motors of the robot to provide desired motion.


·         SENSORS

Sensors are required to detect position of the line to be followed with respect to the robot’s position. Most widely used sensors for the line follower robot are PHOTOSENSERS. They are based on the basic observation that “the white surface reflects the light and the black surface absorbs it”.

 Sensor circuit contains emitter, detector and comparator assembly.


IR or VISIBLE light is emitted from the emitter (IR light is mostly preferred to avoid interference from the visible light which is generally around the robot. However IR light is also present in atmosphere but its intensity is much less than that of visible light, so IR light can give much reliable output. For better accuracy of the sensors, they must be covered properly for the isolation from the surrounding.)

 This emitted light strikes the surface and gets reflected back. If the surface is white, more intensity of light gets reflected and for black surface very less intensity of light is reflected.

 Photo detector is used to detect the intensity of light reflected. The corresponding analog voltage is induced based on the intensity of reflected light. This voltage is compared with the fixed reference voltage in comparator circuit and hence it is converted into logic 0 or logic 1 which can be used by the controller.

The comparator circuit may be designed in two ways.



Black area=1

White area=0



Black area=0

White area=1

 In the following section, case-1 is used.


Vcc is 5V power supply.

Input+ is non-inverting input terminal of an op-amp =V(+).

Input- is inverting input terminal of an op-amp=V().

Output is either logic1 or logic 0 depending upon both input terminals.

Output is Logic 1 if V(+) > V()

                Logic 0 if V(+) < V(-)



A= centre point of voltage divider circuit (always 2.5V)

B= Non-inverting terminal of OP-AMP

C= Inverting terminal of OP-AMP

D=Output terminal of OP-AMP




·         When light falls on detector D2, a voltage drop of around 0.7V occurs across D2 and hence 2.5V (voltage at A) – 0.9*V (drop across D2) = 1.6*V (voltage at C)

·         When light does not falls on detector D2, no current flows through it and hence voltage at C = Voltage at A =2.5V


*These values will be change with change in atmosphere, lighting conditions etc. We have to change variable resistor to get the desired output.


Now let us see various conditions as given in the table below.


Voltage at A

Voltage at B

Voltage at C

Voltage at D



Less than 2*V

If light falls,(white area) 1.6*V


Logic 0


Less than 2*V

If light does not fall,(black area)



Logic 1


Greater than 2*V

If light falls,(white area) 1.6*V


Logic 1


Greater than 2*V and less than 2.5V

If light does not fall,(black area)



Logic 0

 If voltage at C is greater than 2.5V, the output will be always at logic 1. This condition must be avoided.

 *These values will be change with change in atmosphere, lighting conditions etc. We have to adjust variable resistor to get the desired output.



 It is a special type of resistor. Its resistance is dependent upon the intensity of light falling upon it.

 It has wide range of resistance depending upon the intensity of light. Its resistance can vary from few ohms to some kilo-ohms or even more.

 To use LDR, above circuits with the following modifications can be used.

1.      Use visible LED instead of IR emitter.

2.      Replace detector with LDR.
Wait while more posts are being loaded