To help my kids celebrate Mother’s Day this year, I wanted to do something a little different. Instead of just a present, I wanted the kids to be able to give her something a bit more one-of-a-kind.
I’d bought an ATtiny85 to play with some of the ATtiny Arduino support (or failing that, work out how to use avr-gcc directly). I also had a bunch of very bright LEDs and some cheapy cell batteries sitting around doing nothing.
First, I took one of the spiffy cases from when we bought some kids’ earrings recently, and drilled holes to shape out a heart.
Poking the LEDs through, I kept the cathodes all in the centre, so I could bend them all inwards and haphazardly solder them all together. I also used wire to bridge each LED with its opposite, so I’m driving a ring of ten LEDs with five pins.
Finally, I soldered the pre-programmed ATtiny85 to the LED anodes, using a small piece of electrical tape to ensure it isn’t going to inadvertently touch any of the mess below it. The cells (wrapped in electrical tape) go directly to the power & ground pins on the chip, and a resistor feeds the ground to the LED cathodes.
Except I made an off-by-one error in my sketch that I didn’t notice during testing (c % 6, instead of c % 5). Thankfully, I was able to fairly easily solder on wires to a 6-pin ISP header and flash a new program.
The source code is available here: https://github.com/mibus/MibusArduino/tree/master/MothersDayFlasher