I want to add external push button to Parallella's GPIO pins. Is it correct to connect push button just like the users did for Raspberry pi boards? enter image description here
if it's working, what resistor should I use? and if it's not correct, what schematic should I follow to connect push-button to one of the GPIOs?
I just had a quick look at the Parallella schematic. It is 17 pages with rather a lot of connections so I can't do a full analysis in a few minutes. (I would also need to work through the datasheet)
You must check which voltage your I/O pin is operating at. If it is 3V3 you can use the schematic as-is. If it is a different voltage you have to replace the 3V3 with whatever the I/O voltage is. For the rest the principle is OK: Pull the port low with a resistor and use a push button to the selected voltage to make it active high.
If you don't know which voltage to use set the pin in output mode and output a 'high' Then measure which voltage appears.
Note that in general it is safer way to use a resistor (e.g. 50KOhm) to tie the pin to the I/O voltage. Then use a push button to pull the pin low. If you make a mistake, the pin is more likely to survive as the resistor limits the current.
