I am building a large array of Light Switched relays, and due to the size of the array i want to keep the part count down.
Each 'Pixel module' has a 12V SPDT, bulb and an activate-on-dark circuit. There is a strong spotlight on the device and the viewers shadow is obscuring the light in their shadow so the swing is large.
I have seen the obvious LDR-and-Pot circuits with a junction out to a NPN Transistor, and the more stable comparator alternative
I was looking at "solar cell" types of Photodiodes (PiN Type), and I can't see why I cannot just lay one across a PNP transistor (Collector to Base?) or something so it applies a Base voltage when lit up.
Can someone briefly explain to me why I am wrong? I figure it would be all over the net if it was that easy, and i cant find any examples!
Is this possibly the cheapest way to make a light switched 12V relay driver?
Note: I prefer solutions using discrete circuitry, as I have a thing for human readability, visual components etc :P