Idea is to be a halfway step between a Cortex M4 board and an A9-style board, using no more than 0.5W of power (100 mA at 5V or 150 mA at 3.7V, say) when running flat out. I imagine something like the board in the old Ben Nanonote if you're familiar with those. E.g. basic specs like:
- 300 mhz or so Ingenic or Pic32 (MIPS) processor
- 32MB or 64MB ram
- MicroSD slot
- Lipo charger
- Realtime clock, maybe with a low power user-programmable MCU (AVR picopower, MSP430 etc) that could run when the main cpu is off
- MicroUSB device/power with auto lipo charge, like Adafruit feather boards
- GPIO, SPI, etc. No ethernet or USB host.
- small board, like 2x4 cm or smaller if possible, but this is not critical
- castellated edge holes or could have a thru-hole version that can take pins
The main idea here is to have the convenience of Linux software development and memory protection, not to have a super powerful computing device. It should not have HDMI or anything like that since it's for embedded use in something powered by a small battery. Boards like the Raspberry Pi (even the model zero) use way too much power.
Not too hard to get the Pi Zero down to 80mA.
John
On Adafruit it says you have to use a 1 amp 5 volt adapter, i.e. don't plug it into a computer because voltage sag can corrupt the SD card. Sure the Zero's minimum power draw is low. The issue is the maximum draw, not the minimum.
Added: it would be really nice if the board could run on a lipo cell without needing a bunch of power conversion components for step-up to 5v.
Plenty of boards can do approx. what you want. Just pick the one you want. That'll just need effort.
If you want an exact match to every detail you may have to make one. Costs of custom PCBs are very low.
John
The iMX233 OlinuXino Nano looks pretty close to what I want, though there are no power consumption measurements given. It doesn't seem real easy to find such boards though maybe I don't know where to look. I'm a programmer not a hardware designer so building my own board is not feasible.