title: Arduino uno overheating
body: <p>I tried to get digital reading on my arduino uno board to check if 5V signal is on or off.
  When I plugged it in digital pin 9 it got really hot really fast. Also it couldn't give me correct readings on A0 analog input. Later it worked fine on digital pin 8. I know that pin 9 can be used to provide PWM output but i thought that they can also be used as regular digital input pins. How can I use this pin as digital input?</p>