In the design process I set several goals:
- Controlled by an AVR ATtiny13
- Interfaced with 1 push button
- Driven by ~3v of unregulated power
- Incorporate an auto-off function to simulate the candles burning out each night.
I chose the tiny13 because I had several on hand just collecting dust. In order to control 9 leds without a shift register (a separate part) I needed to implement a charlieplex
A schematic is available below.
For those electrical engineers reading this, I have two points to make:
1. I did not use a pull-up resistor for the reset pin, it is left floating. This is not a critical application so if we have a random reset it's not the end of the world.
2. I did not use a decoupling capacitor because I'm using unregulated power and I don't think it's essential.