Solar system power for esp8266 device like weather sensor. You need 5V 0.15W solar panel and small li-po battery for example 200mAh. Zener diode stabilizes voltage on 4.3, schottky diode give 0.15-0.2V voltage drop because 4.3V is too much for li-ion battery and prevents lekage current from battery. You can use panel also like binary(0/1) light sensor.
Keep It Simple Stupid
Not tested yet.
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
As title says, 2 very simple PCBs with schematics
schottky diode and capacitor (ceramic / electrolytic doesn't matter) is part of smoothing and can be skipped for standard LED's, but it's needed e.g for self changing color ones
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.