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.
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.