digital pin output = 1V

Forum 2005-2010 (read only) Hardware Troubleshooting
1

my digital pin 4 only output 1V when i send digitalWrite(4, HIGH)...

my board is a 5V board.

i measure it against the board's ground...

any idea why?

2

have you set that pin as an output using pinMode(4, OUTPUT)?

If not, you are measuring the 5V through the 20K internal pull-up resistor - http://arduino.cc/en/Tutorial/DigitalPins

From that page:

Note that the pullup resistors provide enough current to dimly light an LED connected to a pin that has been configured as an input. If LED's in a project seem to be working, but very dimly, this is likely what is going on, and the programmer has forgotten to use pinMode() to set the pins to outputs.
3

I've found the culprit...

newbie mistake, a stupid one. my bad.

i added a diode after pin4, which meant to protect from reverse voltage, not expecting voltage drop as much as close to 4V.

I've read the article, and i didn't know that too. now i do.

thank you very much...