Forget LED Matrices, How About Neon!

The low-cost LED has changed the way we approach lighting in all its forms, allowing complex addressable displays and all sorts of lighting goodness. But what did we do before we had cheap LED arrays? Use neon bulbs, perhaps? That’s exactly what [Manawyrm] has done with her chainable 8×8 neon matrix boards, taking 64 neon indicator bulbs and driving each from mains potential with an individual triac. A line of 74HC595s handle the data transfer, floating at mains voltage while their ESP32 driver is kept safe by a set of isolators.

A Twitter post shows it in action, but perhaps the most hackworthy praise should be reserved for the test rig. Unable to source a variable 230 V mains supply for testing the array, she applied a 50 Hz sine wave to an audio power amplifier, and replaced the speaker with the low voltage side of a mains transformer. It’s the sort of hack we can’t help liking.

Neons have generally featured here as novelties rather than as significant displays in their own right. They’re interesting components that everyone should have a play with, not least because the possess negative resistance, and can be made to oscillate.

16 thoughts on “Forget LED Matrices, How About Neon!

    1. A stereo amp makes a fine driver for stepper motors too, once you bridge over the dc-blocking capacitor: driven by quadrature sine waves it makes an essentially “infinite” microstep drive. Very quiet too.

        1. It is possible to use an amplifier module harvested from a broken car stereo coupled to three 230V/12V transformers for a small three-phase VFD.
          Bolted to a chunky heat sink one of those 4*40W cheap car stereo standard ICs can put out about .15 Amps at 400V 3~AC in delta configuration with three 50W halogen lamp transformers connected “backwards”.
          Enough to spin up a big gyro compass or drive a 1/8hp synchronous three phase motor.
          Just connect a phase-shifter to your function generator, solder a couple of capacitors and resistors to the amplifier chip according to the datasheet’s standard schematic and away you go.
          Be careful when spinning up three-phase Motors to insane speeds, tho.
          At about 500Hz a pre-war 1/8hp synchronous motor found in your dad’s attic explodes quite violently…

    2. Three of the test machines we use at work, Teradyne Eagle production automated test systems that our manufacturing group use to test every chip that comes out of our fab, have a pair of professional-grade concert audio amps in the main tower, because it uses a 19khz AC supply to power all the resources in the test head. So they synthesize a 19khz signal and feed it into the two audio amps and get almost a kilowatt out of each one, that feed the two halves of the test head card cage.
      I’ve always tried to be careful with my hearing, wear hearing protection a lot of the time, and I’m the only person who works in that lab who can hear the whine of the supplies running. It’s really irritating, so I wear hearing protection… but I can tell when one of the systems has a supply failure.

    3. Putting things in reverse–

      Can’t remember the firm, but there was, at one time, a US manufacturer of high-quality power supplies which–to demonstrate the frequency response (and high quality) of its power supplies–created an application note showcasing one of its supplies being used as an audio amplifier.
      All you young squirts: tune out; this was in the days of linear (analog) power supplies, of course.
      Maybe I can find the app note…

  1. This reminded me of something different.
    Back in the 1980s, the TV/Appliance store I worked at had a clear plastic box, about 10 cm on a side, and about 3 cm tall.
    It had a “matrix” of neon bulbs (maybe 36?) with the leads cut off; fixed inside.

    It was placed in a microwave oven to show customers how the microwaves could (or failed, depending on brand) to reach the corners of the oven. It was only intended to be used for a few seconds at a time.

  2. You can use transformers to get to the 230V from 120V.
    – If your transformer have 120/240V windings on the primary side, then it could be used as an auto-transformer. Feed 120V into one of the winding, you’ll get 120V from the other one.
    – If you have 2 identical transformers e.g. 12V output, connect the two 12V sides. Feed power into one of them and you’ll get 120V back out.

    In both cases, connect the 120V output with the AC in series in the correct phase to get 240V.

  3. I would be extremely interested in knowing of a reputable source of JEDEC- or EIA- compatible neon indicator lamps / bulbs, of many different types. Are any of the traditional neon-lamp suppliers, such as GE or Signetics, still in the business?

    Pay close attention to the word “reputable”; this includes the ability to purchase–from a catalog–again, a year from now.

  4. Back on the old DEW Line in Canada we had remodeled the bar. Someone thought some blue bamboo screens would make a good substitute for a dark blue sky. Then someone else wanted stars in the sky: solution? Lots of neon bulbs, each with a different RC network for different time constants all hooked up in parallel to a 90 volt battery. Worked great! The Air Force inspectors who came by twice a year said we had the best looking bar on the DEW L ine.

        1. As a kid, I bought a 90V Everready battery “for experimental purposes”. I just had to peek inside, so I peeled back the cardboard cover to reveal what should have been obvious: Ten 9V batteries in a stack, series connected.

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