I'm trying to find a circuit or Photocell that will run on 4-5 volts and turn off a small transmitter at night, I have a 6 volt solar cell with voltage dropped to 5 volts going into a charge controller that is powering a transmitter and charging a 3.7 volt battery for backup, I would like it to turn off the battery when the sun goes down as it doesn't need to work at night but can't find a photocell or similar device that does that, also need it to be small, anyone have a idea or where that could be found?