Bumpy is a DIY mp3 player based on ATMEGA32U4 @ 8MHz and VS1003 for mp3 decoding IC. It’s powered from a Li-Ion battery and Max1555 manages battery charging. TPS2112APW is used to automatically switch between USB and battery power. The design is full open source and materials costs about $58 USD for a single board.
Bumpy is a small homemade mp3 player, with features similar to an iPod shuffle. The entire design is open-source, from the firmware to the circuit board to the 3D-printed case. Bumpy plays .mp3 files off of a micro-SD card. You can load files onto the card then plug it into Bumpy, or plug Bumpy into your computer: it will show up like a flash drive (though it’s a bit slower).
Bumpy – a DIY MP3 Player based on ATMEGA32U4 - [Link]
mic @ wemakethings.net writes:
For a long time I wanted to enter the 21st century by stopping using NiCad or NiMH batteries and upgrading to Lithium accumulators as they provide more power per volume and are cool in general. Constant flow of obsolete cell phones provides a nice source of reasonably high-performance batteries for free – I felt compelled to tap into this resource for my battery operated projects.
Open source Lithium battery charger modules - [Link]
Alex at Tinkerlog writes:
For my latest projects I used a lot of single cell LiPo batteries. They are really nice. High power density, low self-discharge, no memory effect and they can deliver quite an amount of current. But LiPo battery handling is a bit more complicated than other rechargeable batteries. You have to take care of under voltage and over charging as that may destroy the battery.
I used the Sparkfun LiPoly charger, based on MAX1555, for some time and it works really well. The only thing I missed was a way to control the current. After some research I decided to try another chip, the Microchip MCP73833. [via]
LiPoly charging with MCP73833 - [Link]