vinceherman:
How fast does it initialize?
I have seen threads here that have a circuit that wakes up when a button is pushed, runs to completion and then powers down.
Not very fast. at least 0.5s to call the file; not ideal for initialization on power up, but I might try this as I search for alternative methods. Thanks!
PaulRB:
Low Power Labs Motino M0 is an example of a samd21 based Arduino compatible board with very low power sleep modes. It can wake from sleep on an external interrupt which could be caused by a button press. They also sell a low power SD card module.Here is a high efficiency amplifier board with a pin which can be used to shut it down into a low power sleep (I think - the SW pin).
Here is a tutorial on playing WAV files with Arduino Zero.
For 36 buttons, you could organise them into a 6 x 6 matrix. 12 digital pins would be needed to read them. The 6 row pins would be set to INPUT_PULLUP and the 6 column pins to OUTPUT & LOW. If any button is pressed, one of the input pins would be pulled low. These pins could be set to interrupt & wake the chip from low power sleep, I think. The chip would then check which pin had been pulled low. This would indicate the row of the pressed switch in the matrix. The chip would then set the column pins to INPUT_PULLUP and the row pins to OUTPUT & LOW. The column pins could then be read to determine the column of the pressed switch in the matrix.
Wow, thanks Paul.
I will do some research around this board and specifically that chip. I am sure I could get a little shield which would house the amplifier and some diodes for the matrix for easy soldering. I will update this thread as I find out more.
Thanks again to both of you!