voltage drop on output pin(s)

Hi, I've got a problem that I'm hoping someone might have an answer to: if I upload a sketch setting a pin to "high", my board (Uno)will only send out a voltage of 2.5. However, if I disconnect the wire from the circuit, my multimeter reads 5 volts. Soon as I try to connect that same wire back to a circuit, the voltage again drops to 2.5. I've made sure my wirings correct, grounded (both circuit and arduino), etc, and it keeps dropping the output by half. I've tried to even plug the arduino into a blank breadboard (one thats still grounded) and the moment the wire is inserted, I get the same drop. This happens with any pin I use: 5 volts switches to 2.5 the moment its connected to anything. Oh, and I've checked w two multimeters, on w a brand new battery, so thats not the issue. Please, if anyone has a suggestion as to whats going on, I'd love to hear from you. Thanks in advance

In setup... pinMode( YourOutputPinNumberGoesHere, OUTPUT );

Thanks for that suggestion, but honestly its not an issue with the code. I've been using this board for a while now, with 100% success. When this started happening I went back through absolutely everything, including back tracking to the code itself, on some weird off-chance I had done something along the lines of your suggestion. The code doesn't seem to be where the problems coming from. Any other ideas?


  1. Whatever you have connected to the wire is drawing too much current.

  2. The processor is damaged.

Everything you describe suggests you haven’t set the pinMode to Output. You mentioned “backtracking through the code” but have you gone back to the basics? Upload a very simple sketch and verify the auduino behaves the same way?

Remember any pin that is not set to an output is an input by default. So it would not be a surprise that when any kind of load is connected (even just a multimeter) the voltage drops.

Lastly, the micro does not “send out” voltage. It raises the voltage to a certain level. As already mentioned, the voltage drops when too much current is drawn.