I have a device that uses a DC motor operated by two solar cells in series. The device has a switch on it to run the motor from a AA battery when sunlight is not strong enough to operate the motor. There is a 5 ohm resistor in series with the battery to lower the voltage on the motor. Rather than manually switch from solar to battery power and back again, I would like a circuit that would sense the drop in voltage from the solar cells and automatically connect the battery then restore solar operation when the sun is bright again. I would also like to include an ambient light sensor circuit to disconnect the battery at night because the device only needs to operate in daylight hours. Please suggest circuits to meet the above objectives.