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I have connected digital pin 2 of arduino to the circuit as shown: pin 2 to 1kOhm resistor to base of 2N222 transistor. Emitter to -ve of 9v battery. Collector to -ve of LED, +ve of LED to 330Ohm resistor, resistor to +9v The problem is that the LED is not turning on normally its only turning on when I touch anything on collector side of circuit. What seems to be the reason? Seems like grounding problem as its turning off when I don't touch my legs to ground. turns on when I touch it

Thank you in advance.

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  • if that's an npn, it's (probably) backwards. you also need to common the ground with the MCU
    – dandavis
    Mar 11 '17 at 11:40
  • Hint: Use wires intended for breadboards. The battery wires lack pins.
    – Mikael Patel
    Mar 11 '17 at 12:50
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Sounds like you have guessed it: although it's very hard to say from those photos, it doesn't look like you have the circuit grounded.

Connect a ground from the Arduino to the black wire from the battery.

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  • Yes, you are right its working now. Thank you very much :D.
    – Teja Allani
    Mar 12 '17 at 8:00
  • Sorry for the photos, I uploaded this from my phone and I put connections in image descriptions, but they are not visible in the post.
    – Teja Allani
    Mar 12 '17 at 8:04

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