OpenVac: An open-source low-cost fine vacuum sensor

When it comes to moisture- or air-sensitive chemicals, often the Schlenk technique is used to achieve safe and reliable results. In this article, we present an open-source and low-cost microcontroller-based alternative for vacuum sensors for this application. In Schlenk technique, the atmosphere in the reaction apparatus is replaced with an inert gas like argon or nitrogen. To do so, the apparatus first needs to be evacuated. To monitor the pressure level, vacuum sensors are used. Commercially available vacuum sensors typically are expensive and hard or even impossible to repair. Thus, we like to present our open-source and low-cost alternative, which uses a Pirani-type sensor and a Wheatstone bridge. The cross-voltage in this bridge circuit is amplified by an OpAmp and converted into a digital signal through a 12-bit ADC. The processing of this data is achieved through an ATtiny84, which also controls a 0.91-inch OLED display to show the current pressure. The device is battery powered and optimized for long runtime.