Colour Sensor

Colour sensor is an interesting project for hobbyists. The circuit can sense eight colors, i.e. blue, green and red (primary colours); magenta, yellow and cyan (secondary colours); and black and white. The object whose colour is required to be detected should be placed in front of the system. And based on the colour placed the corresponding LEDs will glow

Circuit Digram:

Components Required:

R1,R2,R3,R4,R5,R6,R7,R8     :      1k
R9,R10,R11                            :      220k
VR1,VR2,VR3                        :      10k
LDR1                                      :      Blue
LDR2                                      :      Green
LDR3                                      :      Red
LED1   to   LED7                     : Blue , Green , Red , Maganta , Cyan , Yellow , Black  , White
IC1(N1 - N3 )                          :     CD4073B
IC2(N4 - N6 )                          :     CD4073B
IC3(N7 - N8)                           :     CD4073B
IC4(N9 - N14)                         :     CD4069B
IC5(N15 - N20)                       :     CD4069B
Filter Circuit(May be filter paper )


Circuit Description:

The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered. The circuit makes use of AND gates CD 4073and NOT gates CD4069 IC .The output of the three LDR are connected to the CD4073 directly and by inverting the output of not gate and then it is connected to the CD4073 .
When a primary coloured light ray falls on the system, the glass plate corresponding to that primary colour will allow that specific light to pass through. But the other two glass plates will not allow any light to pass through. Thus only one LDR will get triggered and the gate output corresponding to that LDR will become logic 1 to indicate which colour it is. Here in this case of detection of a primary colour red the LDR which is in front of the red glass filter only get activated. That is when we are placing red light in front of the product then the output of the red filter is red light. Red filter means it reflect only that colour and all other colour are absorbed by it hence in this case only one LDR are in high state and the other output of the LDR are in the logic low state so in this case the output of it inverted and it is made logic high state and it is given to the and ic CD4073 then the output corresponding the red light that mean the red LED will glow.
In this case of detection of a primary colour green the LDR which is in front of the green glass filter only get activated. That is when we are placing green light in front of the product then the output of the green filter is green light. green filter means it reflect only that colour and all other colour are absorbed by it hence in this case only one LDR are in high state and the other output of the LDR are in the logic low state so in this case the output of it inverted and it is made logic high state and it is given to the and ic CD4073 then the output corresponding the green light that mean the green LED will glow.
In this case of detection of a primary colour blue the LDR which is infront of the blue glass filter only get activated. That is when we are placing blue light in front of the product then the output of the blue filter is blue light. Blue filter means it reflect only that colour and all other colour are absorbed by it hence in this case only one LDR are in high state and the other output of the LDR are in the logic low state so in this case the output of it inverted and it is made logic high state and it is given to the and ic CD4073 then the output corresponding the blue light that mean the blue LED will glow.
Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corresponding to the mixed colour will allow that light to pass through while the remaining one will not allow any light ray to pass through it. As a result two of the LDRs get triggered and the gate output corresponding to these will become logic 1 and indicate which colour it is. Thus in this case since two of the LDR are at logic high state the output of the other LDR are connected to the inverter IC and it made high and then it is connected to the AND IC as one of the input and two input are connected directly to the AND IC thus based on this input output colour corresponding to this means the led corresponding to this will glow. so when we place white light in front of the system all the LDR get triggered. in this case the output of all LDR are connected directly to the AND gate since all the input to the and gate is high then the output will be also in high state .thus white light will glow as the indication of that colour. When all the LDRs get triggered or remain un triggered, you will observe white and black light indications respectively.