Uno: Output from Pin#8 is ~1.2V pulse signals instead of 5V pulse signal


I encountered a weird issue on an Arduino Uno today, and been trying to understand why it happened but have no clue. Please help out if you had this problem before or know how to fix it.

Basically I have a code to output pulse signals through pin#8 (Low = 0V, and High = ~5V). The code worked great yesterday, but today from some reason it scales down my signal to a ~1.2V pulse signal. The pulse width and frequency are correct as expected. 5V and 3.3V pins output correct values. I can re-program and upload the code into the Uno successfully but the issue is still there. Is that an MCU problem or a board problem?

Since I have could borrow an Uno from my friend, I tested it with the same code and that Uno gave me the right signal. Hence, I believe my code works properly.

Any clue to fix my lovely Uno?


Sounds like you have damaged that pin, most likely by pulling too much current for too long from it. You can screw up any number of boards by wiring them up and 'testing' that code.

Check that pinMode is use to set pin 8 to output. Check your wiring. Making good contact with pin 8 & Gnd? What is pin 8 connected to? Did you use a current limit resistor? Does the chip feel warm or hot to the touch? That's a good sign an IO pin was damaged and failure of the entire chip may be imminent.

Make a simple program to write the pin HIGH for 10 seconds and then LOW for 10 seconds and measure the voltage. If you are not getting 5v and 0v something must be damaged.


Hi Want is your application and what is the output pin connected to?

Thanks... Tom.. :)

Without actually looking at your configuration, it is hard to say, but 1.2v sounds suspiciously like something (LED without resistor?) is clamping the output. You indicate it works fine on a friends board, but not yours, but is his connected to the same whatever your board is connected to? What is connected to the pin in question?