Camera Sees Electromagnetic Interference Using An SDR And Machine Vision

It’s one thing to know that your device is leaking electromagnetic interference (EMI), but if you really want to solve the problem, it might be helpful to know where the emissions are coming from. This heat-mapping EMI probe will answer that question, with style. It uses a webcam to record an EMI probe and the overlay a heat map of the interference on the image itself.

Regular readers will note that the hardware end of [Charles Grassin]’s EMI mapper bears a strong resemblance to the EMC probe made from semi-rigid coax we featured recently. Built as a cheap DIY substitute for an expensive off-the-shelf probe set for electromagnetic testing, the probe was super simple: just a semi-rigid coax jumper with one SMA plug lopped off and the raw end looped back and soldered. Connected to an SDR dongle, the probe proved useful for tracking down noisy circuits.

[Charles]’ project takes that a step further by adding a camera that looks down upon the device under test. OpenCV is used to track the probe, which is moved over the DUT manually with the help of an augmented reality display that helps track coverage, with a Python script recording its position and the RF power measurements. The video below shows the capture process and what the data looks like when reassembled as an overlay on top of the device.

Even if EMC testing isn’t your thing, this one seems like a lot of fun for the curious. [Charles] has kindly made the sources available on GitHub, so this is a great project to just knock out quickly and start mapping.

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A DIY EMC Probe From Semi-Rigid Coax And An SDR

Do you have an EMC probe in your toolkit? Probably not, unless you’re in the business of electromagnetic compatibility testing or getting a product ready for the regulatory compliance process. Usually such probes are used in anechoic chambers and connected to sophisticated gear like spectrum analyzers – expensive stuff. But there are ways to probe the electromagnetic mysteries of your projects on the cheap, as this DIY EMC testing setup proves.

As with many projects, [dimtass]’ build was inspired by a video over on EEVblog, where [Dave] made a simple EMC probe from a length of semi-rigid coax cable. At $10, it’s a cheap solution, but lacking a spectrum analyzer like the one that [Dave] plugged his cheap probe into, [dimtass] went a different way. With the homemade probe plugged into an RTL-SDR dongle and SDR# running on a PC, [dimtass] was able to get a decent approximation of a spectrum analyzer, at least when tested against a 10-MHz oven-controlled crystal oscillator. It’s not the same thing as a dedicated spectrum analyzer – limited bandwidth, higher noise, and not calibrated – but it works well enough, and as [dimtass] points out, infinitely hackable through the SDR# API. The probe even works decently when plugged right into a DSO with the FFT function running.

Again, neither of these setups is a substitute for proper EMC testing, but it’ll probably do for the home gamer. If you want to check out the lengths the pros go through to make sure their products don’t spew signals, check out [Jenny]’s overview of the EMC testing process.

[via RTL-SDR.com]

One Man’s Tale Of EMC Compliance Testing

If you turn over almost any electronic device, you should find all those compliance logos: CE, FCC, UL, TÜV, and friends. They mean that the device meets required standards set by a particular region or testing organisation, and is safe for you, the consumer.

Among those standards are those concerning EMC, or ElectroMagnetic Compatibility. These ensure that the device neither emits RF radiation such that it might interfere with anything in its surroundings, nor is it unusually susceptible to radiation from those surroundings. Achieving a pass in those tests is something of a black art, and it’s one that [Pero] has detailed his exposure to in the process of seeing a large 3-phase power supply through them. It’s a lengthy, and fascinating post.

He takes us through a basic though slightly redacted look at the device itself, before describing the testing process, and the EMC lab. These are fascinating places with expert staff who can really help, though they are extremely expensive to book time in. Since the test involves a mains power supply he describes the Line Impedance Stabilisation Network, or LISN, whose job is to safely filter away the RF component on the mains cable, and present a uniform impedance to the device.

In the end his device failed its test, and he was only able to achieve a pass with a bit of that black magic involving the RF compliance engineer’s secret weapons: copper tape and ferrite rings. [Pero] and his colleagues are going to have to redesign their shielding.

We’ve covered our visits to the EMC test lab here before.

An Overview Of The Dreaded EMC Tests

There is one man whose hour-long sessions in my company give me days of stress and worry. He can be found in a soundless and windowless room deep in the bowels of an anonymous building in a town on the outskirts of London. You’ve probably driven past it or others like it worldwide, without being aware of the sinister instruments  that lie within.

The man in question is sometimes there to please the demands of the State, but there’s nothing too scary about him. Instead he’s an engineer and expert in electromagnetic compatibility, and the windowless room is a metal-walled and RF-proof EMC lab lined with ferrite tiles and conductive foam spikes. I’m there with the friend on whose work I lend a hand from time to time, and we’re about to discover whether all our efforts have been in vain as the piece of equipment over which we’ve toiled faces a battery of RF-related tests. As before when I’ve described working on products of this nature the specifics are subject to NDAs and in this case there is a strict no-cameras policy at the EMC lab, so yet again my apologies as any pictures and specifics will be generic.

There are two broadly different sets of tests which our equipment will face: RF radiation, and RF injection. In simple terms: what RF does it emit, and what happens when you push RF into it through its connectors and cables? We’ll look at each in turn as a broad overview pitched at those who’ve never seen inside an EMC lab, sadly there simply isn’t enough space in a Hackaday article to cover every nuance.

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