I've got a PIR sensor triggering a solenoid via arduino and a 2N2222 transistor. I'm running 15v into the circuit, but am only getting around 2v at the solenoid. I'm a n00b and could definately use some help in figuring out what transistor I need. I was advised to replace the 2N2222 with a relay, but the relay switches too slow.
also, the 2N2222 gets REALLY hot, so i'm quite sure i'm losing a ton of voltage to it.
So - are you going to share a schematic and specs on the solenoid with us, or what?
Seriously - before we can even begin to truly diagnose the issue, we need this information.
My initial guesses:
1) You don't have the circuit hooked up right
2) You aren't using a base current limiting resistor to the Arduino
3) You need a different (larger) NPN transistor, as the solenoid's current needs are higher
However, without seeing your schematic and/or hook-up, along with specs on the solenoid - all of the above are simply guesses, at best.