Just a little note on where I sourced some of the components:
Yes, it is the cheap-o USB travel charger.
This little thing had many good parts required for this project:
- Step up converter
- Li+ charger IC
- Li+ Battery
It also has a battery protection IC but I decided not to use it in this project.
The step-up converter used in travel charger is responsible of providing 5V out of Li+ battery which can be anywhere from 3.7V to 4.2V.
However, in my project, I actually step up the solar panel voltage to 5V and power the Li+ charger IC from it, which in turn charges the battery. Then the battery is being used through a MAX8888 LDO to power the ATmega328P and nRF24L01+ module.
The 1W LEDs are directly connected to the battery and switched on via N channel MOSFETs.