To start I definitely wanted a built in Lipo battery (the original VMU chews through CR2032s and I didn't want this device to continue that legacy). So I've opted for a tiny chip I have used in the past and have a number in stock, the MAX1555. I did a little test fitting in the shell and unfortunately in order for the battery to fit I will need to cut away the coin cell battery holder plastics in the shell. The battery I chose was a tiny 220mAh battery pulled from a sandisk sansa mp3 player. The original Arduboy sports a super thin 180mAh battery so we are off to a good start.
The second major feature I wanted to add was a soft power button since the VMU has a sleep button anyway. To achieve this I opted for the MAX16054, basically a low power digital toggle switch. The output of this on/off switch goes to the enable of the 3.3V regulator that drops the lipo's ~4V down so I can safely and directly interface the main chip, a Atmega32U4, with the 0.9" SSD1306 OLED and the onboard 8MB serial flash to store hundreds of games. Finally, in relation to power, the quiescent draw of the MAX16054 is anywhere from 7-20uA so given the 220mAh battery capacity the standby time theoretically sits around 1.26-3.59 years (very rough estimate and likely only to be half that if I'm lucky). Still I though it would be a good idea to add a physical power switch (hidden under the top cap next to the usb port) to cut off the battery for long term storage.
So the first pcb/schematic design ended up looking like this:
Not pretty, and hopefully the measurements I took from the original VMU pcb with the help of my calipers are close enough for everything to fit. I managed to order the boards just in time before the Chinese new year started so in the next log I will post the results of pcb v1.0!