A keypad user has reported a non destructive problem when using the on/off switch on the +13.8V line.It shows as a faint LED when the keypad is off, and blinks when keys are pressed.
This is probably caused by the internals of the uC that let some voltage through from input pins. And TXD line is at +5V in stand-by, as long as
I have investigated a BJT/FET buffer on the TXD line, but didn't solve the problem.
So the simplest solution is to use a DPST switch that disconnects both +13.8V and TXD lines. This mod should be possible on all already built keypads.
