Fifteen Flat CRTs And A Bunch Of Magnets Make For Interactive Fun

If you were a curious child growing up when TVs were universally equipped with cathode ray tubes, chances are good that you discovered the effect a magnet can have on a beam of electrons. Watching the picture on the family TV warp and twist like a funhouse mirror was good clean fun, or at least it was right up to the point where you permanently damaged a color CRT by warping the shadow mask with a particularly powerful speaker magnet — ask us how we know.

To bring this experience to a generation who may never have seen a CRT display in their lives, [Niklas Roy] developed “Deflektron”, an interactive display for a science museum in Switzerland. The CRTs that [Niklas] chose for the exhibit were the flat-ish monochrome tubes that were used in video doorbell systems in the late 2000s, like the one [Bitluni] used for his CRT Game Boy. After locating fifteen of these things — probably the biggest hack here — they were stripped out of their cases and mounted into custom modules. The modules were then mounted into a console that looks a little like an 80s synthesizer.

In use, each monitor displays video from a camera mounted to the module. Users then get to use a selection of tethered neodymium magnets to warp and distort their faces on the screen. [Niklas] put a lot of thought into both the interactivity of the exhibit, plus the practical realities of a public installation, which will likely take quite a beating. He’s no stranger to such public displays, of course — you might remember his interactive public fountain, or this cyborg baby in a window.

46 thoughts on “Fifteen Flat CRTs And A Bunch Of Magnets Make For Interactive Fun

    1. When I was young my wealthy friends had a color TV, my moderately wealthy friends had a black and white TV. My parents had a TV that only could display the color black. Although there was a time when it did show more than that, a bright flash followed by a loud bang, that was an exiting evening although that happened only once. Because the TV could only show black it was perfect for imagining scifi space programs, deep deep space programs, or programs that were about black holes.
      Ahhh… imagination, it was a wonderful thing to have.

    2. When I was a kid, the magnets I couid gat ahold of were pretty weak. Magnets from 3v motors and 3inch speakers.

      It got better as a teenager, someone gave me the magnet off a good speaker.

      Now, just open a hard drive, and the small magnets are dangerous. Though I guess those are disappearing with SSD drives.

  1. Back in the day I took apart a microwave oven and extracted the very strong magnets. They were great fun to play with. You could put them on a dowel and levitate the upper magnet. Eventually I gave them to my 10 year old son and told him to keep them away from our TV and magnetic tapes as in cassettes. He was curious about what would happen and about 20 minutes later I heard dad, look at the TV. Sure enough, there was a round multi colored donut burned into the picture that images seemed to be attracted to like a black hole. Curiously, the shape of the black hole donut matched the shape of the magnet I just gave my son. High drama ensued and the magnets were confiscated. But eventually, the donut faded away and the picture went back to its normal operation. It’s great to see a museum have a similar display for showing how electron beams can be deflected with a magnet. Simple hands on displays like this make a big impression, even without the drama.

    1. I’m pretty sure all you needed to do to fix that spot was a degauss cycle. Or, if the one built into the TV wasn’t powerful enough, they made external handheld degaussers that would do it.

    2. when i read there are magnets in a microwave, i felt stupid that i never harvested them from the microwave i threw out a couple years ago. then i thought about what little i know about microwave magnetrons and i don’t think they have fixed magnets? why are there magnets in your microwave? what am i missing?

      1. The fixed magnetic field is required to make electrons emitted from the cathode to “orbit” around it in a radius proportional to the applied field. The anode has a number of resonant cavities. The interaction between the magnetic B field and the E field along with the resonant cavities sustains the microwave frequency oscillation. A small stub antenna extracts microwave energy from the tube to heat up your food.

    3. it’s hard to really damage the shadow mask, the issue is more often that you just magnetise it…
      using a powerful external degauss coil is generally enough… the built in degauss coil that shot when you turn the TV on is generally not enough to recover from a heavy magnetisation…

      1. “it’s hard to really damage the shadow mask”

        True, but not impossible. There were a couple that the external deguassing coil couldn’t clear.

        1. I can attest that a 25″ TV falling from about 4 feet onto a carpeted floor can bend a corner of the shadow mask permanently while the rest of the device continued to function normally.

          (Very front heavy RCA TV on top of an 80’s rack system cabinet + cat that disappeared for many hours that day)

    4. When I was a kid fixing TV sets, I couldn’t afford a commercial degaussing coil, so I made my own from one found in a 25″ set and added a cord and switch. It worked great, but since it was intended to operate for a few seconds with a PTC resistor in series, you had work fast; it got pretty hot otherwise!

      1. I was told to wrap long lamp cord wire x number of times around the base of a (circular) wastebasket (to give it a toroidal shape) and wrap it with electrical tape and attach an electrical plug to it.
        (I’ve forgotten the wire guage and number of turns around the wastebasket, but the coil was over an inch thick)

    1. They have terrible geometry and the p4 phosphor the use burns in very quickly. They’re OK for the original purpose (viewing moving images) but they’re not great for computer displays.

  2. At a pinch you could use a 100 watt Weller soldering iron, switch it on, move it around the crt a bit then off. The field was generally strong enough to degaus the metalwork and let the little electrons land in their correct places.

  3. I developed a magnet motor that produces usable torque and RPM. It can easily drive a generator and make plugging in EVs obsolete. Buildings can be 100% off grid. Feel free to contact me for further information

  4. These were most likely out of a aiphone systems. The display and tube were at right angles to each other but the display was mostly un-keystoned. Fun little devices for their day.

    Not much of a hack to find them though, they were still in use until very recently, and only now being taken out of buildings.

  5. I’m a pilot, quite inebriated
    My plane’s control, I have vacillated
    But fear not folks, I’ll tell you a story
    Of a curious child, in the days of CRT glory

    With magnets, a funhouse mirror they’d make
    Twirling and twisting, their favorite pastime to take
    But beware, a warning before it’s too late
    For a powerful magnet, can damage that CRT plate

    Now Niklas, he’s built a display so neat
    For science museum, it can’t be beat
    Monochrome tubes, from video doorbells he scored
    And a console, of an 80s synth, it adored

    Each monitor, a camera does face
    With magnets, distortions, it’ll replace
    Public installation, it can withstand
    Niklas, the master, of interactive art and command.

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