For the last couple of weeks, my son and I have been building “Digital Dice” as a project to teach him some hardware and software design, and to play settlers of catan, with out wiping out whole villages with “real” dice.
The requirements were:
- emulate two die faces
- have shake detect to roll
- coin cell power
- rechargeable over usb
- longish battery life
We designed this thing using protel. The first cut of software I did using the arduino environment. I hate to admit it, but is is pretty easy, although the I2C library is broken with respect to the freescale accelerometer in the default installation. I’ve attached the schematic. Gerbers and code are available, if you are interested leave a comment. The circuit uses:
- atmega328p (pico power cpu)
- mma7660 accelerometer
- LIR2032 battery (rechargable)
- MCP73832 charger.
Where is the low voltage cutoff protection circuit?
I never really thought about the low voltage cutoff. The MCU has a low voltage cutoff/brownout protection enabled, and in practice the whole circuit seems robust enough. I get a about a week on a charge. The standby current is still pretty high though ~ 300uA
Nice circuit, by the way.