OpenCVMeter is an open source tool to measure capacitance and leakage current as a function of a capacitor’s working voltage.
When designing circuits, many hobbyists take capacitors for granted, but as it turns out, not all are created equal. Each type (ceramic multi-layer, aluminum electrolytic, tantalum, mica, etc.) has its own unique properties. Nowadays, ceramic capacitors are the most commonly used ones in the industry, yet many can lose up to 80% of their rated capacitance near their voltage ratings. This can be a problem.
This is something that one Swiss engineer set out to solve. The project is the brainchild of Mathieu Stephan, a project manager on the Hackaday-influenced Mooltipass offline password keeper.
“Not every electronics enthusiast knows that a ceramic capacitor’s capacitance changes with the voltage you apply to it. This can be particularly annoying when designing RC filters or DC/DC power supplies” Stephan explains. “You might therefore think your capacitor’s value is 10uF when it actually is 1.8uF because of the way you’re using it. Moreover, the graph displayed above isn’t so easy to find in a capacitor’s datasheet… and it sometimes simply isn’t there.”
Cognizant of this, the OpenCVMeter is an open source tool that measures capacitance and leakage current as a function of a capacitor’s working voltage. This meter is capable of providing an accurate capacitance versus voltage characterization within 1%.
There are many scenarios where capacitance is critical to the correct functioning of the circuit, including analog RC filters (signal processing, audio applications), DC-to-DC power supply design, and decoupling applications to name just a few.
In some cases, a lower than specified capacitance may lead to sporadic hardware bugs, or in the extreme, a non-working device. According to Stephan, OpenCVMeter will give you the information you need to make sure this doesn’t happen in your next prototype. Additionally, the OpenCVMeter can measure currents up to 12.4uA with a resolution of 6nA, which can be extremely useful when designing ultra low-power gadgets.
For instance, Stephan notes that you could use the OpenCVMeter to verify that all your passive components, adhere to their leakage specifications, and ensure your device has maximum battery life.
What’s nice is that the OpenCVMeter doesn’t require any drivers and works right out of the box with your Windows, Linux or Mac computer. This allows you to set the maximum voltage when characterizing capacitance or leakage current, specify the number of points for the generated curve, save the curve data points to a .CSV file, use the OpenCVMeter as a standard capacitance meter, as well as easily upgrade your unit’s firmware.
In terms of hardware, the OpenCVMeter is entirely open source and built around the mighty ATXmega16A4u. These electronics are housed inside a grey anodized aluminum enclosure. It has two standard banana sockets, and comes with SMD tweezers, test hook cables and a current calibration kit consisting of three resistors.
This portable box can evaluate the capacitance of a part over a voltage range from 1.3 to 15.5V. By attaching the SMD tweezers or test clips to a capacitor, the OpenCVMeter ramps up the voltage and computes the capacitance of the part through the test cycle. This data is then sent over to a Chrome app, where a graph of a cap’s ability is displayed on the screen.
Interested? Head over to the OpenCVMeter’s Kickstarter campaign, where Stephan is currently seeking $9,959. Delivery is set for February 2016. Those wishing to learn more about its inner workings can also check out the engineer’s writeup here.