Troll physics: 3 LEDs powered by hand

[Henryk] just sent us his latest episode of simple LED circuit puzzles. In front of the camera he solders one pin of each of the 3 LEDs to a different switch. He then puts the three assemblies in his hand and flips each switch to make the corresponding LED come on. We look forward to your explanations in the comments.

You may remember two other videos that [Henryk] made (also embedded after the break). The first video was a simple circuit with a resistor, three switches, and three LEDs in series. When a battery was connected, the LEDs were somehow switched on one at a time.The second video featured the same resistor/switches/LEDs, this time in a parallel circuit. Turning on the first switch made the first LED light up, and the second switch made the second LED light up.

Here are the few other troll physics projects we featured: the original LED circuits post, the super deluxe edition and the amazing solution to the trickery.


  1. mal says:

    I hate to be a naysayer, but do we really have to have this sort of post? This isn’t a hack, and this site isn’t sleight-of-hand or troll a-day.

  2. password says:

    This guy is really amazing with this stuff.

  3. mclien says:

    Hope I don’t repeat someone. (Can’t see the comments from this PC).

    My guess: The hand is just distraction (what else?). And all other tricks have AC involved:
    – you can power nearly an LED bulb on a single cord by adjusting the wavelenght of a AC power supply, thus having a “standing wave”, which has a peak of the wave all time at the exact same length (where the LED sits). So every cycle of the AC the LED is “hit” by the amplitude of that. With high enough frequency neither the eye nor the film will catch it.
    Powersupply most likely a goldcap inside the switches.
    Perhaps the AC crap isn’t necessary at all, given a high enough voltage and a low enough current, so the hand works fine as resistor…

  4. NiN says:

    LEDs probably have small capacitors soldered on their leads, and hand + LED makes resonant circuit. He has transmitting coil somewhere around. LEDs use few miliamps so it is possible to turn them on this way. My guess.

  5. valdas says:

    witchcraft! burn him! :D

  6. Jim Turner says:

    this guys videos are a lot of fun. if you know his tricks, please keep it to yourself so you dont spoil the magic!

  7. Midnight says:

    My guess.. he has some small batteries in the switches and his hand functions as ground

    • ffdsafsad says:

      I don’t think so, the voltage is too low to work through just your hand or sweaty hand at that.

      • jpa says:

        I just tried and if I lick my fingers, I can get a red LED light up with just 18V. 40V would probably be enough to get it as bright as in the video, and still be safe.

        • Dax says:

          4.5 volts is enough to get a LED to light up all the way across both arms. I just tried it, and sure enough you get a dim glow as long as you lick your fingertips first.

          I’m measuring 20 microamps across the arms, and that corresponds roughly to 250 Kohm, but it’s still enough to light a LED. 45 Volts would therefore make about 0.2 mA while the LED in question needs about 5 mA to shine brightly.

          • Norse says:

            Anyone messing around with this method — please note that just 10mA across the heart can cause ventricular fibrillation and kill you.

  8. Lion says:

    Power switch has embebed power source right? he just needs something to act as ground? is that it? :S

  9. Alexandru says:

    This is a master troller, and the effort put into hiding how they work and the quality of the finish is more than I bother with my own projects.
    See the other videos in his youtube channel for the solutions.

  10. Indyaner says:

    In the YT comments he agrees when someone finds a correct solution. He links to his google+ Account where all shematics are available.

    He really is into soldering tiny things :D

  11. documentsofaninsignificantcarbonbasedlifeform says:

    My guess: lvl 9 wizard
    >Not sure if should fear or not
    >Depends on alignment

  12. rexy666 says:

    My best guest is that the LEDs aren’t simply LEDs. The switches aren’t simple switches. And the battery isn’t just a battery.

  13. mattbed says:

    I think everyone is over thinking this
    Its just a rework of this:
    A battery and tansistor and a resistor are hidden inside the switch and the two “probes” are the lead of the LED and the tab of the switch

    • zygomatic says:

      I can’t view the schematic from work, but this is my guess too – a darlington array circuit and battery inside the switch. The darlington array amplifies a tiny amount of current through the skin and switches on the LED.

  14. ino says:

    first guess: he uses a coin cell and a high frequency switching mode power supply in each switch to close the circuit over the skin, getting rid off the skin internal impedance.

  15. Dave says:

    I remember seeing a lot of online discussions when he started posting his puzzles. I don’t really care and I’m just too much of a n00b to guess how he does it…

    I just hope he isn’t a prick and tells people how he did it, instead of letting them guess and guess and guess…

  16. aztraph says:

    Oh! HIM again? Ever since his revealing video of how he did one of these hacks last time, it’s like yeah, so what, we know the schtick. I applaud the skills to be sure, but once everyone knows the trick it becomes more mundane. now get to work on that perpetual motion machine.

    • Greenaum says:

      For the last one I looked at, he didn’t give the solution for MONTHS. It’s a nice fun idea but if you’re gonna torture people like this, at least put us out of our misery in a fair amount of time. Otherwise it just gets annoying.

  17. jim says:

    I think he is using movie fx grade liquid latex to hide small leads in his finger tips and down the side of his hand…he has it rigged so when he pokes his fingers with the edges of the led lead and switch leads he is able to power the circuit.

    • LordNothing says:

      you know, he could be completing the circuit with his blood stream.kinda dangerous/insane/stupid, but it could be a thing. he is applying a lot of pressure on those leads. ive stabbed myself with components before, totally on accident of course.

  18. Rollyn01 says:

    Static electricity. All he has to do is is use the LEDs as diodes to have the flow of discharge go in one direction. He can sent the charge using the skin-effect while a electo-static generator sends the charge off-screen. This way, he doesn’t get shocked and only the LEDs light up due to the pathway they provide as the body tries to naturally restore the nuetral electrical potential on his skin.

  19. Augur says:

    I think he has some kind of clear conductive paint on the inside of his hand. His palm looks allot lighter in color than the back..

  20. Alejandro says:

    He solders the LED lead to one of the rocker terminals and then makes a swaping motion as if he solders another wire to the other lead.
    My gues: battery in the switches and a very fine lead from the other LED lead to the second rocker terminal.

  21. LouLou says:

    I don’t understand what the big deal is.

    I just did the exact same thing in the video and it worked just fine.

    It’s all about following instructions. C’mon guys.

  22. KillerBug says:

    I’m guessing he has a coin cell and something to make a high frequency pulse or AC hidden inside the switches…it might make the skin tingle a little but it wouldn’t be dangerous to use fingers as a ground path so long as you used some moisturizer first.

  23. Justaguy says:

    Maybe you could construct a return path using another wire running back along the LED leads. It’d have to be separately insulated, and very thin to be concealed along the other wire. A voltage source hidden in the switch could power the circuit…
    the real issue is that the solder bridges the supply and return of the circuit, which leads me to suspect DC current… maybe more electrikery in the switch to allow voltage out without immediately returning to ground? Last time, he used some pretty slick frequency math to “bend” logical rules of electricity, so he’s totally capable of digital signal manipulation on a very fine level. perhaps ninja soldering skills to a second unoberved terminal.
    Realistically though, I’m fairly certain black demon magic is somehow involved…

  24. uri says:

    I am NOT going to waste brain cells trying to second guess him, I enjoyed the presentation knowing what I saw was illusion as far as the visible circuits went.
    Well Done Sleight of Hacker !

  25. villekl says:

    For those really interested I recommend checking the solutions on his google+ account. The skill and amount of work he puts into these is awesome!

  26. Jon says:

    This one is to easy. There is a power source (battery) in the switch and his hand is acting as a ground plane.

  27. syko82 says:

    Battery in the switch, his hand is the ground plane.

  28. hemalchevli says:

    This dude has serious soldering skills.

  29. He’s demonstrated his skill at concealing coils in the LED base, so maybe they’re powered by induction. The leads may just be a control circuit.

  30. spoko says:

  31. physicist says:

    There is a battery in switch and he soaked his hand in salty water and dried so his hand acts as a conductor.

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