Happy Halloween!
Last year I built a collection of plywood pumpkins to stick in the yard on Halloween night. I installed superbright LED's in the eyes, nose, mouth, etc and was pretty pleased with the results. This year I want to animate the LED's.
I bought a DLP-245PL which uses a PIC18LF8720 to drive it's digital I/O. I need a simple transistor circuit to drive each LED. There's about 22 of them. Typical LED voltage is 2.1V to 3.4V, current ranges from 20mA to 30mA.
Last year I was driving the LED's from a simple 12V DC power supply. Their cathodes are connected together and to ground. The anodes connected to appropriate resistors. For the life of me, I can't remember the equations appropriate for switching transistors.
It seems like optoisolators are a bit of overkill. Things I'm worried about are the base resistor and transistor selection, and the possibility of sending 12V into the TTL outputs of the PIC. It would be nice to reuse the transistors I have on hand, which are: 2n2222a, tip34, 2n3906.
chuck