continuity

5 Articles

Your Multimeter Might Be Lying To You

April 10, 2023 by 33 Comments

Multimeters are indispensable tools when working on electronics. It’s almost impossible to build any but the most basic of circuits without one to test and troubleshoot potential issues, and they make possible a large array of measurement capabilities that are not easily performed otherwise. But when things start getting a little more complex it’s important to know their limitations, specifically around what they will tell you about circuits designed for high frequency. [watersstanton] explains in this video while troubleshooting an antenna circuit for ham radio.

The issue that often confuses people new to radio or other high-frequency projects revolves around the continuity testing function found on most multimeters. While useful for testing wiring and making sure connections are solid, they typically only test using DC. When applying AC to the same circuits, inductors start to offer higher impedance and capacitors lower impedance, up to the point that they become open and short circuits respectively. The same happens to transformers, but can also most antennas which often look like short circuits to ground at DC but can offer just enough impedance at their designed frequency to efficiently resonate and send out radio waves.

This can give some confusing readings, such as when testing to make sure that a RF connector isn’t shorted out after soldering it to a coaxial cable for example. If an antenna is connected to the other side, it’s possible a meter will show a short at DC which might indicate a flaw in the soldering of the connector if the user isn’t mindful of this high-frequency impedance. We actually featured a unique antenna design recently that’s built entirely on a PCB that would show this DC short but behaves surprisingly well when sending out WiFi signals.

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Peer-Reviewed Continuity Tester

September 30, 2022 by 10 Comments

One of the core features of the scientific community is the concept of “peer review” where any claims made by a scientist are open to be analyzed and reproduced by others in the community for independent verification. This leads to either rejection of ideas which can’t be reproduced, or strengthening of those ideas when they are. In this community we typically only feature the first step of this process, the original projects from various builders, but we don’t often see someone taking those instructions and “peer reviewing” someone’s build. This is one of those rare cases.

[oxullo] came across [Leo]’s original build for the ultimate continuity tester. This design is much more sensitive than the function which is built in to most multi-meters, and when building this tool specifically some other refinements can be built in as well. [oxullo] began by starting with the original designs, but made several small modifications. Most of these were changing to surface-mount parts, and switching some components for ones already available. Even then, there was still a mistake in the PCB which was eventually corrected. The case for this build is also 3D printed instead of being made out of metal, and with the original video to work from the rest fell into place easily.

[oxullo] is getting comparable results with this continuity tester, so we can officially say that this design is peer reviewed and tested to the highest of standards. If you’re in need of a more sensitive continuity sensor, or just don’t want to shell out for a Fluke meter when you don’t need the rest of its capabilities, this is the way to go. And don’t forget to check out our original write-up for this tester if you missed it the first time around.

Schematic-o-matic

Tricked-Out Breadboard Automatically Draws Schematics Of Whatever You Build

December 6, 2021 by 18 Comments

When it comes to electronic design, breadboarding a circuit is the fun part — the creative juices flow, parts come and go, jumpers build into a tangled mess, but it’s all worth it when the circuit finally comes to life. Then comes the “What have I done?” phase, where you’ve got to backtrack through the circuit to document exactly how you built it. If only there was a better way.

Thanks to [Nick Bild], there is, in the form of the “Schematic-o-matic”, which aims to automate the breadboard documentation process. The trick is using a breadboard where each bus bar is connected to an IO pin on an Arduino Due. A program runs through each point on the breadboard, running a continuity test to see if there’s a jumper connecting them. A Python program then uses the connection list, along with some basic information about where components are plugged into the board, to generate a KiCad schematic.

[Nick] admits the schematics are crude at this point, and that it’s a bit inconvenient to remove some components, like ICs, from the breadboard first to prevent false readings. But this seems like one of those things where getting 80% of the work done automatically and worrying about the rest later is a big win. Plus, we can see a path forward to automatic IC probing, and even measurement of passive components too. But even as it is, it’s a great tool.

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Build An Everlasting Continuity Tester

July 13, 2020 by 34 Comments

When you need a continuity tester at the bench, what do you reach for? Probably your multimeter, right? It may surprise you to know that the continuity tester in the meter isn’t all that sensitive, even if it’s the yellow expensive kind. [Leo]’s will beep even if there is 50Ω of resistance in the line.

Disgusted by modern commercial testers, [Leo] set out to make the ideal continuity tester in the spirit of old school tools that do one thing and do it really well. It had to be simple to use, always ready to go, and capable of measuring continuity at 5Ω or less resistance (video, embedded below).