sensors and ldr

Posted on Feb 6, 2014

Color sensor is an interesting project for hobbyists. The circuit can sense eight colors, i. e. blue, green and red (primary colors); magenta, yellow and cyan (secondary colors); and black and white. The circuit is based on the fundamentals of optics and digital electronics. The object whose color is required to be detected should be placed in fron

sensors and ldr
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t of the system. 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 colored filter glass plates determine which of the LDRs would get triggered. The circuit makes use of only G ‹ •AND • gates and •NOT • gates. When a primary colored light ray falls on the system, the glass plate corresponding to that primary color 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 color it is. Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corres- ponding 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 color it is. When all the LDRs get triggered or remain untriggered, you will observe white and black light indications respectively. Following points may be carefully noted...

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