Michael Teeuw’s son Luca recently turned one, and while special birthday cakes online delivery traditionally have a small flame on top of them in the form of a candle, Teeuw (logically) decided that a one-year-old was not to be trusted with fire. Instead, he did what any responsible hacker-dad would do and created a faux candle on a PCB to act as the “flame.”
This candle uses a MEMS microphone and amplifier to detect sound, and thus blowing, and an ATtiny85 to simulate a blinking flame. Amplified sound signals are fed into the microcontroller’s ADC, which controls three LEDs via PWM. While the ATtiny85 normally only allows PWM output on two pins, this was possible per a technique outlined here.
The candle PCB was designed in KiCad 5.1 in the 40mm shape of a standard tea light, and includes a CR2032 battery holder as well as the microphone on the backside. While the build was a success, it should be pointed out that the microphone used here is dwarfed by a 2 Euro coin. Teeuw admits he was a bit intimidated, but was able to properly solder it into place.
One final bit of trickery involved building an actual flame shape with hot glue to better simulate the a candle. The build was a success, as Luca reportedly had a great birthday, with no danger of fire involved!
