Shade/Sun Switch

[Mavrik]

I'm looking for a simple circuit that will turn on when sun rays hit it and off when in shade. I tried a transistor with a photocell, but the photocell is way too sensitive. I would like something that is transistor controlled if possible.

[JMACgyver]

[quote="Mavrik"]I'm looking for a simple circuit that will turn on when sun rays hit it and off when in shade. I tried a transistor with a photocell, but the photocell is way too sensitive. I would like something that is transistor controlled if possible.[/quote]

Ok, first thoughts...

there are two types of photocells: a) photo-resistor, and b) photodiode.
my understanding is a photoresistor's output will vary proportionally with the light level. you can get them in many varieties, the most popular being either positive- or negative-coefficient; meaning either resistance goes down when light hits them, or the resistance goes up when light hits them. Which one you use depends on what you're trying to detect, i.e., light, or dark.

a photodiode's output, if i remember correctly, is either on/off (conducting or not conducting), or linear (as opposed to proportional) I could be wrong about this, hopefully someone can chime in if so.

let's assume you're using a generic CdS photoresistor. Is the sensitivity issue you're experiencing the the detection range too narrow? or is it the light level it triggers at too variable?

for the first issue, i would suggest an array of cells spread out to maximize detection range, but your circuit will need to be altered to taske into account the new resistances.

for the second issue, you would have to come up with a 'trigger' range of resistance, and add probably a Schottkey buffer to stabilize the output of the cell.

hope this helps, or at least points you in the right direction.
--David--
aka Electro