A switched solar cell charger for LiPo batteries (4.2 V) with a 8-pin Atmel ATTINY13. Required hardware: more information on my blog site
Update: This Project includes also a ATTiny25 project. Because the ATTiny25 could output a 325 kHz PWM. PB0 @ ATTiny13 is PB1 @ ATTiny25 !
GPLv2
Atmel Studio 6.2