This is the analogue part of the circuite for my Arduino battery charger project.
The software can be found at https://github.com/GarethDaviesLondon/PWM-Charge-Controller-Arduino.
The pin outs refer to an Arduino Nano.
The key to this project was to make the Nano go to sleep when the sun wasn't shining.
This is an analogue circuit for a battery charger.
Undervoltage the unit is "hard on" then it oscilates around the desired set voltage forming almost a PWM style switching near full charge.
This circuit pulls about 10ma making the losses to this low.
More efficiency could be obtained from the solar panels using MPPT