Build simple colour detector circuit for line tracking robots.

The given circuit is tested by myself in NCE Robotics Club ( www.facebook.com/ncerobotics ) many times with various modifications, the given circuit works very effectively.

Figure: Verified circuit diagram of color detector

The circuit can detect two different colors comparing the light reflecting capacity of those colors. As we know the light reflecting capacity of brighter color is higher than dark one, thus the different intensity of light reflected by different color surface will cause the different value of resistance in LDR ( Light Dependent Resistor ) sensor, which is converted into voltage levels by implementing LDR and a fixed resistor in voltage divider arrangement (but as fixed resistor we use preset to change the sensitivity as our desire and required level).

In above circuit, 100 ohm resistor is used to light LED1 safely with high intensity, The LDR and a preset is used as voltage divider and gives the primary output of sensor which will changes as the color of reflecting surface changes. Two 10 k ohm resistors gives the fixed ( reference ) voltage to the negative terminal of comparator which is compared with the input from sensor primary output in non-inverting terminal. when the sensor primary output is below the reference voltage the sensor gives low output ( indicator is off ) and when the sensor primary output is above the reference voltage the sensor gives high output ( indicator is on). In this way the above circuit detects the colors.

For example in case of white and black color the sensor gives high output for white color and low output for black color. This logic can be altered by altering the inputs to the comparator.

By arranging these sensors in different numbers and applying as input to the micro-controller for further process we can make a line following robots easily as I have mentioned in earlier posts.