Listening To Mains Power, Part 2

The electricity on the power grid wherever you live in the world will now universally come to you as AC. That is to say that it will oscillate between positive and negative polarity many times every second. The frequency of 50 or 60Hz just happens to be within the frequency range for human hearing. There’s a lot more than this fundamental frequency in the spectrum on the power lines though, and to hear those additional frequencies better you’ll have to do a little bit of signal processing.

We first featured this build back when it was still in its prototyping phase, but since then it’s been completed and used successfully to find a number of anomalies on the local power grid. It takes inputs from the line, isolates them, and feeds them into MATLAB via a sound card where they can be analyzed for frequency content. It’s been completed, including a case, and there are now waterfall diagrams of “mystery” switching harmonics found with the device, plus plots of waveform variation over time. There’s also a video below that has these harmonics converted to audio so you can hear the electricity.

Since we featured it last, [David] also took some feedback from the comments on the first article and improved isolation distances on his PCB, as well as making further PCB enhancements before making the final version. If you’ve ever been curious as to what you might find on the power lines, be sure to take a look at the updates on the project’s page.

26 thoughts on “Listening To Mains Power, Part 2

  1. It’s probably apocryphal, but one of the supposed demo tactics for the venerable Bose 901 speaker was for the shop to plug them in to the mains, drawing their max power handling and playing a very noisy and distorted bass note.

    1. I’m all for letting the weak minded earn their Darwin Awards but I’m not sure it’s ok to help them do so.

      Come on now, 120V @ 8 Ohms = 1,800 Watts.
      220V @ 8 Ohms is 6,050 Watts

      Don’t plug your speaker into the mains unless you are ready to die.

      1. (Hit the report button by mistake, sorry.)

        Somehow I pictured Marty McFly in front of Doc’s speaker setup… that’s arguably not 1.21gigawatts, but still enough to send anyone flying away.

    2. Found a pair of (blown surround etc) 24 inch drivers dumpster diving once. Something similar may have happened to them; way up in the air plant of a school “field house” gymnasium. Dunno if they ever found the source of the horrible noises.

  2. A new low in audio level on YouTube, really low -32dB! When I used Audacity to amplify it, it sounds like a shrill buzz with no hum fundamental, or is that what severe digital downgrading does? Sounds worse than many light dimmers on an AM radio.

  3. Use a few turns of wire around a leg of a mains transformer and feed this into the microphone input of a mixing desk with usb interface (or the microphone input of a soundcard). Then use the “praat” software to analyse the spectrum after having recorded the audio with your computer. I used that method once to monitor some issue with our ripple control at the utility I work. Did cost nothing because as a musician I already had everything needed.

  4. 25 years ago I read some comments in a very thick book which alluded to government data transmission through live power systems. It still makes me wonder if there are any data interfaces coming in through the power bus.

  5. Many years ago a friend of mine worked on monitoring the electric grid in the USA as part of his master’s project. He continued the work at Black Mesa . . . I mean Idaho Falls where he found a quick edit to the <$500 device that would shut down the power grid.

    I regret not asking him for schematics before he flew back to the east coast. On his way to testify to the Department of Energy subcommittee of Congress, the Department of Homeland Security classified his project. He got to DC to find that no one on the subcommittee had proper security clearances to learn about his hack.

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