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.
Continue reading “Microbalance Determines Alcohol Content” →
The clever folks over at [Novaetech SRL] have unveiled openQCM, their open-source quartz crystal microbalance. A QCM measures very minute amounts of mass or mass variation using the piezoelectric properties of quartz crystal. When an object is placed on the surface of this sensor, the changes in the crystal’s resonant frequency can be detected and used to determine its mass in a variety of experimental conditions (air, vacuum, liquid). However, most QCM technology is proprietary and pricey – at least US$3000 for the microbalance itself. Any consumables, such as additional crystals, cost several hundred dollars more.
The openQCM has a sensitivity of 700 picograms. At its core is an Arduino Micro with a custom PCB. The board contains a 10K thermistor for temperature offset readings and the driver for a Pierce oscillator circuit. The quartz crystal frequency is determined by hacking the timer interrupts of the Arduino’s ATmega32u4. An external library called FreqCount uses the clock to count the number of pulses of the TTL signal in a 1 second time frame. This yields quartz crystal frequency resolution of 1Hz. The user interface is built in Java so that data can be read, plotted, and stored on your computer. The entire casing is 3D-printed, and it appears that the sensors are standard oscillator crystals without their cases.
Simplistic design makes assembly and maintenance a breeze. It only weighs 55 grams. Replacing the quartz crystal requires no special tools due to the clip system. The openQCM can be used as a single unit, or in multiples to form a network for all of your precise measurement needs. While they have kits available that will set you back US$500, all of the files and schematics for 3D-printing, assembly, and the PCB are available on the openQCM site for free.
Continue reading “Measure As Little As You Want With OpenQCM” →