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using photo transistor to brighten/dim leds

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Newbie level 3
Oct 25, 2009
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I am working on using a photo transistor to adjust the brightness of a few leds (more light in photo transistor, the brighter the leds). I am trying to figure out the best way to build this circuit. I have played with using transistors to increase the difference supplied by the photo transistor, but I seem to be unsuccessful. Any help designing this circuit would be greatly appreciated.

Variable PWM (using a uP) is the usual way. Otherwise individual controlled current sources would be needed.

I don't really know anything about creating a PWM circuit (nor what a uP is) would you kindly elaborate on how i can go about setting one up?

Have you considered using a LDR Light dependant resistor. The light /current bias is very linear compared to a Photo transistor. it would not be hard to control the current through your diodes with a simple biasing circuit.

i am open to any type of light sensing device. The only qualification is that it need to be reactant to IR light ~940nm, as that is what i am sensing based on. Do you have any recommendations as to what device i want to use, and what a basic circuit would consist of? Basically at no light i would want the leds to be dim, and then as more light is detected (IR) i want the leds to get brighter.

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