FacelessTech's Tiny Breathalyzer Uses a USB Power Bank, ATtiny85, and MQ-3 Alcohol Sensor
Inspired by an earlier build for a USB power bank torch, FacelessTech's mini-breathalyzer is his smallest yet.
FacelessTech has published a new build, and it's a compact variation on a favored theme: an ATtiny85-based, pocket-sized breathalyzer based on the MQ-3 alcohol sensor.
"I’ll admit it I’m obsessed with making breathalyzers," FacelessTech writes. "I made my first one back in 2015 then I made an add-on for the ElectroPet and another add-on for the ZeroBootSystem. I wanted to make a slimmed down version I could take on a night out or to a beer festival. I start out designing it around an Arduino Pro Mini but ended up using an ATtiny85."
FacelessTech had already built a few projects around a USB power bank, including an LED torch in a 3D-printed housing, so it was the natural choice for powering the new design. Coupled with a four-digit seven-segment LED display — the library for which needed minor modification, to remove a serial print instruction not compatible with the ATtiny85 — a custom PCB, fixings, and an MQ-3 alcohol sensor, the bill of materials was complete.
"When I moved to using the ATtiny85 I used a USBtiny to both program it and to power it," FacelessTech notes. "When I moved the ATtiny85 to the PCB I noticed that the MQ-3 was able to draw more power since it was now pulling directly from the power bank and not the USBtiny. I had to re-calibrate [the] sensor. The problem with this is I can’t program the ATtiny85 while it was on the PCB because of the pins I had used.
"So I had to de-solder the ATttiny85 with a hot air work station and transfer it to programming board I had made, Flash the test code which just spat the readings from the sensor out to the 7-segment display. This allowed me to see the base value and then the value when I waved it over a bottle of Jagermeister. I had to de-solder the ATtiny85 again transfer it back to the programming board where I uploaded the now fixed code then transfer it back to the PCB."
The custom PCB is housed, like the torch design before it, in a 3D-printed case which accepts the off-the-shelf power bank. "Most of my project just go into my project draw and don’t get much use," FacelessTech explains. "With using a power bank it wont go to waste and run flat and can be used in other projects too."
Full details on the build can be found on FacelessTech's blog; the source code, 3D printing files, and KiCAD board files can be found on the project GitHub repository.