Thats the problem im having. Its not simple gor me because i kerp getting what seems like all the wrong numbers.
So if the relay coil is 87 ohms at 12 volts I have a draw of 137ma. How do I figure out the base resistor from this? I know the output from the arduino is 5 volts and since this transistor is a darlington pair so I subruct 1.4 from 5 to get 3.6 volts. Whats next?