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.

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Tearing through floppy drives to build a small-format dot matrix printer

The accuracy which [Mario] achieved in his pen plotter dot matrix printer is very remarkable. He tore through a pile of floppy drives to get the parts he wanted, and chose to go with a fine-point Sharpie marker as a print head. In the video after the break he flatters us with a printout of the Hackaday logo, but you also get a look at one problem with the build. The ink doesn’t always flow from the felt tip and he has to coax it (almost like priming a pump) with a piece of scrap paper.

He was inspired by the pen printer we featured back in June. This rendition features a printing area of 1.5×1.5 inches that can accommodate 120×120 black and white pixels. He’s not a microcontroller type of guy and is driving the printer from the parallel port of his computer.

The best printing technique puts the pen down and moves it around just a bit (helps prevent the ink flow problem we mentioned earlier) and produces images like one in the lower right. We love the 8-bit nature of the result and would use this all the time to make our own greeting cards.

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Ask Hackaday: Troll Physics Super Deluxe Edition

Here’s a brain bender for you: YouTube user [Fredzislaw100] put up a video of six LEDs and six switches wired up in series. After soldering a resistor and 9V battery connector, the first switch turns on the first LED, the second switch turns on the second LED, and so on for the rest of the circuit.

We’ve seen this trick before from [Fredzislaw100], only this time he’s moved up from 3 LEDs to 6. In the reveal of the previous trick, [Fredzislaw] built two AC power supplies inside a nine volt battery connector; one high frequency and one low frequency. The low frequency AC line powers the first two LEDs with the help of diodes in the switches and LEDs. The high frequency AC line turns on the third LED with the help of an inductor inside an LED. Apparently [Fredzislaw] still has some soldering skills to show off; the circuit powering this trick is most likely the work of a soldering god.

From a close viewing, it looks like LEDs are wired up in pairs, i.e. LED 1 works the same as LED 2, LED 3 works the same as LED 4, etc. We’ll let Hackaday readers argue it out in the comments as to how this trick is possible.

Tip ‘o the hat to [Th0m4S] for sending this one in.

Doubling up on the USB supercap flashlight

[Antoine] wrote in to let us know that he soldiers on with his flashlight project. He’s doubled up on the supercaps and tripled the LEDs (translated).

The core concept has stayed the same since the original version. He wanted a flashlight that was small and used no batteries. This iteration came about as he looked at increasing the light output of the device. He’s switched to some warm-white LEDs which are easier on the eyes, but was unhappy with the charge life now that he’s using current at a faster rate. The solution, of course, is more potential from the capacitor. He’s now using two 10 Farad caps in parallel. We are a little skeptical about his capacitor theory and ended up using this lecture to defog the issue of parallel and series capacitance.

The upgraded hardware is right at home in that plastic egg like you’d find in a coin-op trinket vending machine. You’ll see there’s still a colored LED to warn when the charge is getting too low.

Followup: Troll physics solved

A month ago, we saw a marvelous demonstration of troll physics from YouTube user [Fredzislaw100]. In his video, we saw a circuit of three switches and three LEDs wired in series and but not acting like the should. A lot of the comments for this post elicited reasonable explanations like modifying the battery or pure camera wizardry via After Effects. Thankfully, [Alan] stepped in and showed us how it was done. The solution uses two AC power sources with diodes in two of the switches and LEDs and inductors in the third pair. [Alan]‘s build was rather large compared to the original video, so we were wondering how this circuit could be made invisible.

[Fredzislaw100] just posted a video on how he did it. Like [Alan]‘s build, it uses two AC power sources, diodes, and inductors. In contrast to every single guess about where the circuit is hidden, the majority of the build is inside the battery connector. [Fredzislaw] did some amazing work hiding a 74LV132 quad NAND Schmitt trigger inside the battery connector. The diodes were easily hidden on LEDs 1 and 3 with some red nail polish, but we’re amazed by the inductor built into the LED seen in the title pic.

So there you go. With a ton of electronics know-how and an extremely steady hand (and a microscope), you too can build your own troll circuit. Check out the video after the break.

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Ask Hackaday: Troll physics edition

[Martin] sent in two videos he found while cruising the tubes. The first video is a simple circuit with a resistor, three switches, and three LEDs. All the components are soldered together right in front of the camera. When a battery is connected, turning the first switch on makes the first LED light up. Turning the second switch on makes the second LED light up, and the same thing goes for the third switch and LED. Obviously we’re dealing with powers that are incomprehensible with even several cups of coffee.

The second video features the same resistor/switches/LEDs, this time in a parallel circuit. Turning on the first switch makes the first LED light up, and the second switch makes the second LED light up. Truly we are dealing with an expert in troll physics.

This is probably something really benign and uninteresting, but it sure is enough to wake up enough brain cells on a Monday morning. We’re not going to hypothesize, so check out the comments where we expect the correct answer to be.

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Driving and old receipt printer

It seems like receipt printers are pretty popular as hacking targets lately. Aside from the wasted paper, they cooler than plain old blinking LEDs and we’d image there’s a ton of them floating around out there as advances in technology have prompted retailers to trade in the bulky dinosaurs for slimmer thermal printers. [Philip Hayton] picked up this Epson model at some type of equipment sale and set to work figuring out how to control it.

This unit is addressed via a parallel interface. After assessing the pinout and searching a bit for protocol information [Philip] hooked up his Arduino and printed out a fitting first message that reads: “Hello World”. He’s got a few tricks you can learn from when trying to talk to hardware with which you are not well acquainted.

Need a reason to go out and find your own receipt printer? Check out this paper-based gaming system for some inspiration. Now develop your own paper recycling setup and we can file this one under ‘green hacks‘.

[Thanks Andy]