pwillard:
Depending on the package metal or epoxy, the 2n2222a can handle between 500 and 800 mA through emitter-collector and the base is quite happy with 5mA to turn on fully.
If the only difference between the 3904 and 2222 is power handling, I should be just fine using a 3904 for driving a 42mA relay, no?
RPCoyle:
It's such a simple circuit.
That's what's got me so f%$@#&* confused, what am I doing wrong? I have tried replacing the transistor, connecting it both ways, replacing the relay, different resistor values, reversing the diode, replacing the diode, even changing the digital pin on the arduino, but yet I still end up losing half the voltage over the transistor. The only thing that works right now is the darlington, which I'd rather not use because it uses up 2 transistors. Here's how it's all wired with just the single transistor, maybe someone will see something that I've overlooked:
