20 kilovolts replaces push pins on this bulletin board

Electrical Engineers don’t need push pins. That’s because they know how to control electrons! [Sven] put his knowledge of these subatomic particles to use when building his high voltage bulletin board. It uses a set of vertically strung wires to keep paper pinned against the board. The wires have high voltage at low current travelling through them. They’re in front of the board, but not touching it, and the board is serving as a ground plane. In this way an electrostatic charge pushes (or should that be pulls?) against the paper to keep each sheet right where he places it.

In the video after the break [Sven] gives us a tour of the hardware at work here. It starts with a 12V psu which feeds a buck converter. The regulated feed is patched into a high voltage supply which was designed as a CCFL driver. Finally, a voltage doubler is used to reach the final voltage, measuring about 20 kV per wire.

Don’t worry, [Sven] says the bare wire is “almost completely safe” because of the low current being conducted.

89 thoughts on “20 kilovolts replaces push pins on this bulletin board

  1. “almost completely safe”

    Got to love qualifiers when talking about safety. There’s only a 0.001% chance it could turn little Billy into an instant cooked Billy meal.

    Great project though. New spin on old idea.

    1. I have had the quote “We’re gonna need another Timmy!” running through my head for the past few days and this just screams that to me. :) Anyone else remember that “Dinosaurs” show on ABC way back in the day?

      1. Not only is this a very interesting topic on hack-a-day, but I’ve learn a new and useful word that I had never heard before. This is hack-a-day at it’s best.

  2. It’s the same as what we used to do for typing tests in elementary school. They would place what we were going to type on the old crt monitors and they would stick. I believe there was some old kids tv show that you could “be a part of” by mailing in for a transparency that you could cling to the crt tv and color on it.

    1. What a horrible idea, considering that TV sets gave off soft X-rays which were the actual reason that the picture tube got ionized.

      It wasn’t much, you’d have to be inches from the screen to get a dose… wait, what was the idea again? Oh, right, sitting inches away from the screen and drawing on it.

      1. Was it really the X-rays? I always thought it’s due to the electrons hitting the fluorescent screen and thus giving the screen a negative charge.

      2. The high voltages used by the CRT cause the static charge. The X-Rays were caused by the electron beam striking the metal mask that separated the colors. Most TVs and monitors had circuitry to prevent the voltages from getting high enough to cause X-Rays. Most CRT tubes were also made with lead-glass for shielding. The bulk of the X-Rays caused by CRTs are actually reflected back toward the rear of the tube – sitting behind a CRT would give more exposure than sitting in front of it.

      3. Yes, it’s not a problem when you’re away from the screen, but it is a problem if you spend time with body parts mere inches away.

        There were/are regulations for picture tubes, but only brand new tubes have to obey them. The problem was that the drive voltage tended to drift, and on more modern sets it drifted intentionally upwards over time to combat the aging phosphor, so a new television set would emit within limits, and an old set would probably be either adjusted or drifted enough to produce harmful amounts of radiation if you were too close to it.

  3. Interesting build, but following the KISS method would have us simply use magnets or push-pins (depending on the type of board), instead of going through all of the trouble of setting up something like this.

    Still, it looks like fun.

    1. Except that pushpins and magnets can get lost or stolen. This is more technically complicated, but it does have the advantage of not requiring any fasteners, so it’s easier on the user end of things. It’s also kind of awesome.

    2. Follow the KISS method would not gave you any hacks. You could just draw in the table with a coal.
      Using high voltage is way cooler… Using dangerous levels of hi-voltage plus ceiling burning lasers plus x-rays or radioactivity would be even cooler, and we could learn a lot in the process…

    3. KISS is for the animals and people who need to be resourceful to survive, but if MacGyver ran out of pushpins and needed to leave a message…

  4. I have several older commercial products that use electrostatic paper hold-down. One is a flat bed pen plotter that you can release the paper with a flip of a switch. It stands vertically. The plotter bed is essentially a very large pcb with an etched alternating trace pattern with a small HV DC supply connected. There is a thin piece of mylar covering the surface. This works *very* well for holding down the paper.

    Another solution would be to go to your local office supply place and purchase some static sign paper and print or write your notices on that. A little rubbing to build a charge and that paper sticks to walls and many surfaces for months! Neat stuff.

    Fun build, though. I like to see projects like this.

    1. The reason i said that it’s almost completely safe is that it is possible to be stupid and use the high voltage for something dangerous, you could for example decide to wrap all the wires in a large sheet of tin foil (making sure it does not touch the wall), creating a relatively huge capacitor.

      Or you could just casually place a large capacitor between a wire and the wall…

      Also if you are stubborn and stand there holding your finger a millimeter or two from the wire, not removing it despite the developing pain, you could get quite serious burns, this is because even though 1mA is a very low current, 1mA and 1kV is still 1W of power developing in a very small area, enough to burn skin after a while.

  5. Cool until the power goes out…
    And how much energy would you say this uses?
    And I’ve done this before, a sheet of glass and and a minute on a vandergraph generator and paper will stick for hours.

    1. Well i supply the CCFL supply with a maximum of 3A and 8V, and assuming some losses in the buck regulator and 230V->12V supply, maybe 30-40W peak. I would say that it draws maybe 10-20W normally.

  6. Is this even green?? I mean, a push pin requires almost nothing to make, lasts for years and the cork is a renewable resource so – what are we GAINING??? It is cool, but really?? A static board for holding paper… if that thought power and voltage power was used elsewhere, could we have a better planet?

    1. Not that many, there has been other high voltage builds in the same room for many years, and unlike this one, some of the others are made to give you a harmless but quite noticeable shock.

      The noticeboard is quite often used to shock others though. If you have on clean shoes with an insulating sole you can hold one of the wires and charge yourself up, then you can release this charge by touching someone else.

      1. Well, see, if you would have explained it like that in the beginning…”so if I help you, Prince Humperdink suffers? I’ll do it”.. then everyone would be building it.

    1. Engineering student actually.

      It is mostly useless and a lot of work to keep it running, but it is above all FUN, and it fits quite well in the recreation room of the electrical engineering program at KTH.

    2. On the contrary, when I was in engineering school us engineers constantly did silly things like this.

      It’s fun, cool, and you learn something.

      We always had the most fun with voltage multipliers, actually.
      And capacitors.
      Used together to blow things up.

      1. .

        I didn’t mean to be rude with my earlier commentary. I apologize for that. But I consider that wasting materials and energy in a problem that could be solved in a much more efficient way is just a crime.

    3. I Agree. As a hack it is quite entertaining, but it solves a problem that does not exist while presenting a couple of more drawback compared to the old cork and push-pin method.

      I see major problems with heavy poster material, laminated paper, tear-off messages and flaps. Things that work by default with a push-pin without the need to waste energy.

  7. You know, I hit one of those CCFL drivers once when I didn’t know it was on. Touched it with my thumb and my hand went numb to about mid-forearm. That was only at 1000ish volts and a few milliamps. I don’t know that I’d want to be anywhere near 20 times that, concurrent drop in amperage be damned.

    1. /agree.

      I’m getting a bit weary of people saying that something is ‘safe’ or ‘relatively-safe’ because of some combination of factors. (This being high voltage at a low amperage.)

      Viewing it like this is dangerous as Electrical Safety is a game of managing multiple variables.

      One (of many) ways of viewing this:
      
      Voltage = Delivery Capacity
      Amperage = Delivery Speed
      
      High Voltage\Low Amperage = More, Slower.
      Low Voltage\High Amperage = Less, Faster.
      
      Both can do damage.
    2. Try a 660v cap, fully charged on a hot day. Was enough for me to sit an pant on the floor for a few minutes. I’d never believed you could experience that much pain until then.

      Broke the nose of the guy that removed the bleed resistor.

    3. His is fed with a buck converter that limits current to 3A at 8V… roughly 0.6mA to the wires, cut in half by the limiting resistors. Doubt you’d even feel it.

      1. The buildup of dust on computer fans seems to suggest that removing the charge that initialy attached the dust doesn’t really do anything :(

      1. Run it under water for a few seconds…

        So they just have to cut power and hose it down to clean it? Those tricky electrical engineering students! I hope they had the plumbing students install floor drains…

  8. “wasting materials and energy in a problem that could be solved in a much more efficient way is just a crime”

    I hope you don’t waste electricity playing games on a computer when cards or dice can be used instead.

    1. Present me with a more energy efficient way to play dice with somebody on the other side of the world and we’ll talk. Perhaps you know a way to roam around fast futuristic worlds that does not require a computer?

      It’s about problems and solutions. This is a solution for a problem that does not exist.

      1. If you fail to see the awesomeness of cork and need to behave like a mid 19th century electo-alchemist and wire it up, then I think the problem is only yours.

        Taking cork for granted. the first insulator for FSM sake! Next thing you’ll be unimpressed by space flight.

    2. I agree, the problem here is that high voltage is awesome, and I require more of it to merge my mind with AC/DC

      Excellent solution

  9. Actually, the flowing current is irrelevant to safety – what’s important is how much it can push through YOU for a short period of time.

  10. Cool!
    It would be fun to attach a little joke circuit to it. For example, when you detect someone coming near the bulletin board, you cut the power randomly for a moment here and there, making the papers slide just a little or fall off. Or disable the power in certain regions where someone is trying to post a new sheet.

    Also I love the phrase almost completely safe, I believe you, but it sounds like the way I would describe my new killer buzz-saw-armed death robot. “He’s almost completely incapable of killing all humans” ;-)

    1. If you reversed the voltage, would the papers then fly off at them?

      Almost completely safe = mostly harmless? sounds like a way to describe earth.

      I read “almost completely safe” and first thought; someone licking it.

  11. What if they just split the board into thin segments. Alternate between positive and ground. This way they can leave the floating wires out and just have all board. Worst case scenario they can also use this board as a bug zapper

    1. that is a thought i have had, the problem is that the board would be significantly more mechanically complex using that strategy, first the whole wall would need to be insulated or built out 10cm to avoid arcs. this would mean about 5 times more material than is used today and a lot more work in getting it to work.

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