With the holiday season upon us, it is useful to be able to determine just how much (or how little) spiking the office party punch has received. [Russell Smith] shows how he tried to determine the proof level of booze using a microbalance made from an old-fashioned panel meter.
That might seem odd, but since alcohol evaporates faster than water, you can plot the change in evaporation rate if you have a good enough scale. That’s where the microbalance comes in. The idea is to weight down the needle of an old meter and measure the amount of current it takes to get to a certain deflection. His results weren’t totally satisfactory, but his methods were interesting.
[Russell] first tried the meter with a power supply and a voltmeter to see how it would work. It did well, but you had to be sure you put the sample in the same spot each time and measured the same deflection. He automated the process using an Arduino and an IR sensor. Although his data showed some correlation to alcohol content, he wasn’t able to get repeatable readings using soaked cotton swabs.