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Topic: basic transistor issue (Read 443 times) previous topic - next topic


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 :)


figured it out - i had to tie the arduino ground to the 12v source ground :)  working as it should now

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