Design and Development of a Low Cost Colour Sensor and its application in Angular Position Control System of a Stepper Motor

The objective of the present paper is to explore an approach of constructing a simple, low cost colour sensor using tri colour RGB model which defines all colours as an additive combination of the primary colours Red, Green and Blue. The sensor consists of a normal Light Dependent Resistor (LDR), surrounded by three Red, Green and Blue LEDs as light source. The LDR and the LEDs are mounted in such a way so that the optical radiation from the LEDs get reflected and falls upon the LDR, the resistivity of which is inversely proportional to the intensity of colour from the LEDs. Therefore, the voltage drop across the LDR is varied whenever the light of different intensities from the LED falls upon it which in turn changes the angular position of the stepper motor. They can be employed for controlling the axial rotation of the stepper motor in robot arm movement to perform some task of manipulation or locomotion under automatic control. The experimental results show that the variation of the resistance of LDR with the change in colour generates an exponential slope and the plot of voltage drop across the LDR with respect to different colour shows a linear slope.