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Grading Capacitors with the Crowd-Funded OpenCVMeter

Gareth Halfacree

OpenCVMeter Kickstarter Model

We've seen numerous tools built on the Arduino platform or the Atmel ATmega microcontrollers that power the most popular models over the years, from SMT soldering paste dispensers, reflow ovens, and oscilloscopes to more specialist tools like a photographic flash tester, ham radio antenna analyser, and Arachnid Labs excellent Tsunami. A project launched late last week on Kickstarter looks to add another to the growing list: a tool for measuring the capacitance and leakage current of any type of capacitor.

Capacitors are a commonly-used component in electronics: put simply, they act as a kind of buffer for electricity. Larger capacitors can be used to supply more current than a power supply could otherwise handle for brief periods, or to replace a battery as a means of retaining settings or keeping a real-time clock ticking while the device is powered off; smaller capacitors can be used to smooth out 'spiky' signals or to decouple one part of a circuit from another. With so many uses, it's no surprise to find that there are an incredible array of types of varying qualities.

The creation of Mathieu Stephan, the OpenCVMeter aims to make it easier for the hobbyist to find suitable capacitors. Based on an ATmega microcontroller and custom circuit, which Mathieu promises will be released under a permissive open source licence when the Kickstarter campaign is over, the OpenCVMeter connects to a host PC via the USB port and allows the user to measure the capacitance to an accuracy of one per cent and ultra-small currents of between 40nA to 12.4uA to 1.5 per cent accuracy and a 6nA resolution. While there are aspects yet to be improved - such as the capacitance measurement range, which currently stretches from 1pF to 200uF - Mathieu's use of an open source licence means it's easy for others to tweak and improve the design to meet their own individual requirements.

The OpenCVMeter campaign is currently running, and has so far raised Fr 2,305 CHF of its Fr 10,000 goal, with 28 days left to go. The 'early bird' rewards, priced at Fr 85, have all been claimed; the current price of the OpenCVMeter is Fr 99 with delivery scheduled for February 2016.

When designing circuits, many hobbyists take capacitors for granted - but each type (ceramic multi-layer, aluminum electrolytic, tantalum, mica...) has its own unique properties. Nowadays, ceramic capacitors are the most commonly used capacitors in the industry, but many can lose up to 80% of their rated capacitance near their voltage ratings. Enter the OpenCVMeter! This meter aims to provide a Capacitance versus Voltage characterization accurate within 1% of the capacitors for your next project (or already have and are starting to wonder about right now...)

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