Simple sump pump monitoring task for use with drmem control system.
This driver uses the RaspberryPi GPIO to monitor the state of a sump pump.
A major requirement is the sump pump cannot be affected by the presence or absense of the RaspberryPi. This was accomplished by using a "current switch" (I am a happy customer of the Dwyer MCS-111050, but there are other, similar products.) I ran the hot wire through the current switch so when the sump pump runs, the relay closes. I configured GPIO4 to be an input with a pull-up resistor so the RaspberryPi can sense the relay's state.