As part of my 2nd year module called Embedded Systems Project at the University of Leeds we were tasked to build a project using an ATMega 328 microcontroller and a series of I/O devices. One of the devices in the lab up for grabs was a simple ethanol sensor (MQ-3) which led me to pursue building a toy breathalyser.
The breathalyser was a handheld device, powered by a 9V battery.
For the project I desiged a PCB and had it fabricated.
An enclosure was designed in SolidWorks cut out from acrylic.
Simple I/O block diagram of the project.
In the end it was an intricate little device, having it's own designed enclosure that I had cut using a laser-cutter in the workshop lab, as well as a dedicated Printed Circuit Board that I designed using EagleCAD. From usability point-of-view it also was quite involved - it had a highscore table stored on the EEPROM, a settings page to adjust LCD backlight and other options and four buttons to navigate/configure the device.
In the end the project received an excellent first and unsurprisingly became an extremely popular party toy amongst my university friends. Eventually the Head of Faculty asked to borrow it for some educational showcase in China. Since then, sadly, I never saw my breathalyser again.