April Fool’s Day is almost upon us. And I, for one, would never pass up an opportunity to mess with someone’s head, even if it is completely expected on this particular day. This year, I decided to put a new spin on a time-tested, oldie-but-goodie: the “coin glued to the ground” gag. I’ve booby-trapped the coin with a piezo igniter so that the “sucker” gets a 30KV shock.

For those of you not in the know, the original setup is just a coin glued to the ground. Unsuspecting dupes come along and see money on the ground and go, “Hey, free money!” Then they proceed to try and pick it up for the next however many minutes. Truth be told, this was me when I was about eight years old, and it was only a nickel. So now, to get my ultimate revenge on the universe, I’m going to add insult to injury with the aforementioned piezo BBQ igniter.

So check out the video. As a very small disclaimer, there are other means I could have used to shock somebody that would have been much more attention-getting – an ignition coil out of a car, for example. Or heck, just wire the quarter to 120VAC (one lead wired to a plate where the victim would stand, of course). Clearly, I’m not out to kill anyone today.

But what about you? Are you working up a good prank this season? Post it in the comments for some #opensourcepranks! (No, it’s not really a thing. But it should be.)


Comments 20 comments

  • There’s always the mind molester - it randomly emits a high frequency chirp that human ears find difficult to locate. For real fiendishness, have it controlled by a photocell so it only works in the dark. When the victim goes to bed the chirps start. When they get up and turn on the light, they stop. And during the daytime, no sound at all.

    With surface-mount parts and a coin battery, it should be next to impossible to find.

    • I made one of these. researched the frequency of a common cricket, and used a arduino nano and a thermistor in addition to the photocell, so that the chirp rate was temperature compensated.

      • Dick Smith Electronics came to my town in the US in the 80s. They had the “Cricket”, kit K-2663. It was successfully annoying.

        But then I ended up living in a Phoenix suburb for a bunch of years, where we had actual crickets living in the walls. It just wasnt funny anymore.

    • I thought for a long time that I had been victimized by such a device. I would periodically hear such chirps in my office, but I never went the distance to actually look for anything cuz I knew it would be impossible to find. Then one day I figured out that the automatic light shut-off circuits we have installed here emit that noise in a lead-up to turning off the lights. This place has made me so paraniod…

  • BTW the SKU for the igniter is COM-10234, not -35!!

  • My favorite electronics prank I did was a few years ago when I was interning at an automotive company. My boss’s boss was on vacation and they always prank him when he’s out.

    I took two backup alarms from garbage and cement trucks and placed them in his office aiming at his chair. I then hooked up a inductive prox to the inside of one of his drawers so when he opened it the alarms would go off. They were very loud and the placement and frequencies caused a strange warble that made it hard to tell which direction the noise was coming from.

    In the end he got in early so we didn’t get to experience his shock firsthand, but he was pretty pleased with it and refused to give the parts back, I’m assuming so he could prank someone else.

    • LOL that’s good. Somebody tried something similar on me a while back, but they failed to consider how much their battery would drain before I got in.

  • I’ve also made one of these.

  • One of my goto pranks is unplugging a phone handset at work, covering the contacts with clear tape, and plugging it back in. Then proceed to call that extension repeatedly. Here is another of my favorites called “pack the cubicle”

  • When I first read the headline quickly, I read it as the “ol' electrified guitar glued to the ground” which seemed really odd. But slowing down and reading it properly, it makes a lot more sense!

    It’s not much work to add a 7805, but the Pro Mini can take up to 12 volts into the Raw input. Any reason you didn’t go that way, and use the Mini’s built in regulator?

    • Next trick: glue an ol' guitar to the ground. Just not an expensive one.

      As far as the ProMini regulator, (12V-5V)*(30mA) = 210mW. On a SOT23-5 package, 210mW is screamin' hot. But it’s a non-issue on a TO-220.

  • Hi Pete!

    Interesting idea. Back in the 80s, I had a coworker who had attended DeVry (in Phoenix), and he told of gluing a quarter onto the railing outside his apartment window, where it would get baked by the Phoenix sun… on a day with “ambient air” of 115+ degrees, you can imagine how hot it would get!

    BTW, my thoughts on the power supply issues would be to have a separate battery to power the “controller” so that any spikes/sags caused by the draw on the servo can’t affect the micro’s supply.

    • That’s one approach that will work. But the battery itself is rated for 25C discharge (if you put any stock in C ratings). The servo is unlikely to draw 25 amps, though I’m not sure what its stall current is. Having a second regulator was easily sufficient - at least on the bench.

      • Rechargable batteries (unless we’re talking “flooded cell”, like in your car) have fairly high internal inductance, so a good sized filter cap (say, 3300uF) might be a good idea. Also, as I learned the hard way when first using 7805s back in the mid-70s, a small ceramic, say, 0.1uF, on each side is also good. (That project, when I finally got a decrepit o'scope and took a look at the 5V line, had 7V peak-to-peak at about 1.5 MHz riding on it. A few filter caps took care of that problem!) The schematic in the video didn’t show any caps on the 7805.

        • Truth be told, I threw that 7805 in there in a hurry and never got back to put the caps in. I didn’t want to lie about it when I drew up the schematic… and now you went and called me out!!

          Shortcuts, kidz. They can bite you in the backside.

        • a small ceramic, say, 0.1uF, on each side is also good.

          I just had an idea for how to implement this for a non-pcb soldering situation. Solder 0805 (or similar) caps directly to the legs right against the body of the TO-220 package. Maybe a 3-hole section of perfboard installed right below the caps to strain-relief the solder connection to the caps.

  • Hi Pete! Why not using a RC BEC circuit? The use almost any cell count lipo (2s up to 5s) and give a steady 5V with plenty amp for the servo. The even come with capacitors to help.

    • Why not? Only because I don’t have one of those as easily accessible as building my own circuit. I’ve got a pile of LM317’s, but I’ve got no languishing BEC’s lying around.

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