When I output a pwm signal from my Arduino Mega 2560 rev 3, the square wave only has a Vpp = 0.5v. How do I get the pwm voltage Vpp = 5V? I been looking around and many articles say its automatically has a Vpp=5 so I don't understand why my is giving 0.5v. I am using a pin with 490Hz and using an analogWrite statement with duty cycle 50%. thank you for your help!
The attached o'scope screen shot doesn't help you fix things, but it does at least validate your thinking of how it ought to be. My sketch used both a 490 and a 980 PWM pin at 50%, and both channels do indeed show 5V.
The moral here is when ever you get an unexpected reading, measure something that you know the voltage of, like the supply rail.
It can happen to the best of us, lead on the wrong setting, like you had or channel switched to zero or the wrong voltage or even a faulty scope lead. I have had the lot but by measuring something you know is right you can eliminate this sort of mistake.