We don't need no stinking 555 timers! We have an AVR in the same form-factor!
The goal of this project is to design an electronic domino using a small AVR chip and minimal components, but at the same time provide a huge amount of flexibility and capability. Here's the 555 version:
And here's the current design:
1. After reviewing the CR2032 spec, looks like it's not sufficient to drive 60 ma - the maximum current required with 3 LEDs on. Fallback is to use 3xAAA batteries, but that's bigger than the device itself! There must be a better solution for powering it.
2. The LEDs used as sensors get cross-illuminated by the adjoining LEDs. Investigate using different wavelength LEDs, shrouds, or some other means to isolate them.
3. For the initial version, was not able to incorporate the switch (too expensive for switch and PCB space). Need to come up with a suitable H/W and S/W solution. Springy wire? Using ATTiny44A provided a complete SPI interface and one extra unused pin!