I need to amplify the output of a digital pin. I need to charge a relay that accepts 3-32vdc. Would a MPS3904 NPN Transistor accomplish this? If yes, what do I connect the base, collector, and emitter to exactly?
Yes, the 3904 should be OK for a small relay. You'll also need a diode and a resistor. Connect:
Diode in parallel with relay coil, cathode end to +5V (so that the diode is non-conducting).
Emitter to ground (0V).
Collector to relay coil and diode.
Base to 1k Ohm resistor, other end of resistor to Arduino pin.
You'll find a number of threads here about relays, some of which have a circuit diagram in them, too.
Try this schematic:
I just use a EIGHT DARLINGTON ARRAY ( ULN28033a ).
"I need to charge a relay that accepts 3-32vdc"
The only relays I'm aware of that can work with a range of 3-32vdc input are solid state relays. Solid state relays only require less then 10ma of current to operate as they use an internal LED to activate the switching. If you do indeed have a solid state relay then it can be directly driven by an Arduino digital output pin, no intermediate switching transistor required. So what kind of relay do you specifically have?
Lefty
Lefty
I was working on the problem already in this thread http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1231727749 but posted this follow up here as well. You can see the link to the specific relay there. The SSR is at the end of a 50' wire run which I think is maybe not allowing it to have enough juice to activate the relay, but I could be wrong. I have a few more experiments to do to verify the relay from the board directly. Thanks for the input.
OK, I've seen that thread also and 50ft of wire on a arduino 4+ vdc output may very well not be able to meet the minimum current to activate the relay and using a transistor to switch a +12 source should work fine.
Good luck
Lefty