Beer Can Breathalyzer
I felt like playing around with DIY electronics, so I built a breathalyzer. It's not an accurate breathalyzer as much as it is a game to see who can get the highest "score". The best part: I housed it in a beer can, so when you blow into it, it looks like you're taking a drink.
The brains of the operation was an Arduino Duemilanove. These things are so cool. It's a motherboard with a firewire-USB interface through which, using Arduino's open source platform, you load a program from your computer that it executes on a loop. I lost the source code since I switched computers, but when on, it would regularly read the output from the alcohol sensor and update the LED gauge. The gauge was calibrated so that one light was about a can of American beer. How did I do the calibration, you ask? Well... believe me, don't drink and solder or else you'll end up cutting off a burnt layer of carpet.
The alcohol detector (the big orange thing on the right) took a while to figure out. It requires just the right resistor to be able to read the output. The one I ended up using was rated at 1,000 +- 5% ohms, with the color code . The sensor needed to cook off the alcohol between uses for an accurate reading, so it ended up using quite a bit of power. I would need to open up the can and replace the 9 volt battery after every evening's use. This took a toll on the integrity of the beer can and all of the wiring, and is the reason I took it apart permanently.