I want to implement a soft power switch on a Panda - like how you switch on a cellphone (hold it down for 3 seconds)…
So usually there is a pushbutton and a MOSFET. The button activates the MOSFET, powers up the Panda and then the Panda “holds” the MOSFET through an IO pin. Simple enough.
The problem I have however is that I want this power button to be one of many on a matrix keypad. The button is not dedicated to the on/off function and it shares a row and column in the matrix with other buttons - so I can’t tie one side of the contact high or low permanently - and it will fluctuate as the matrix is scanned.
Any ideas how to do this?
Is there a way to put the Panda in very deep sleep (drawing micro-amps) and wake it up by keypad?
Is there an IO pin that can sink a current when the processor is not powered at all?