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I need to build a light sensing circuit for a class project. Answered

Hi,

I need to build a light sensing circuit for a class project. I have already built one circuit using a 741 opAmp chip, a 1 meg ohm photo cell, a 1 meg trimmer, a 1k, 100k, and a 47 ohm resister, and a 2n2222 transistor  as well as a 12vdc relay.  The circuit senses the light and the sensitivity can be adjusted by the potentiometer.  It works great for tuning it in to need a certain amount of light intensity to trigger the relay. The problem is i need to be able to put limiting factors on it.  I need to be able to set it to turn the relay on if a certain intensity is reached, but not turn on if the intensity gets to great.  Is there anyone who can help me with the schematics on how to achieve this?

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user
Josehf Murchison (author)2013-04-27

Yes

Use two photo cells and hook it up as a comparator.

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user
steveastrouk (author)2013-04-16

Never ask for help with an electronic problem with a verbal description of your circuit ! POST THE CIRCUIT.

Also, the key concept you need to look for is "Window Comparator"

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