Hi all,
I am pretty new to small scale circuitry/electronics, but have significant background with mains wiring. I am trying to use a 2n3904 transistor to turn a 12v relay on and off. The diagram is attached. output pin 4 from the arduino connects to r1 which is 1k ohm. The circuit isn't working, so I scrapped the relay for an led just to check things out. If i use circuit 2 (attached) where d1 is an led, the circuit doesn't work, but the led grows faintly. It glows faintly even if i disconnect r1 from the arduino - as soon as my fingers touch the resistor wires, it glows. Everything works as it should if I use 5v from the arduino instead of the separate 12v power source. Any idea what the heck is going on here? Thanks 
