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Comment by swebs | Hacker News Reader

I ordered some 2 pin RGB LEDs a few years back. They change color over time via some built in IC, but the crazy thing is that the IC is so small that you can't even see it. And it all fits nicely within a standard LED. I would imagine someone could even fit a similar IC within the traces of a circuit board and nobody would be able to tell.

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All of the puzzles Henryk Gasperowicz makes are this sort of thing. They're fun to try to figure out even if you know the basic idea, as they're pretty much all analog circuits. EG: https://www.youtube.com/watch?v=WvXKSSmItls

Ha-ha... damn, this is so cool! Thanks for the pointer.

Does he ever explain how the tricks work?

He posts full schematics on his google+ page - https://plus.google.com/+HenrykGasperowicz

Here is the schematic for the 3LEDs & 0 switches video liked by GP - https://plus.google.com/photos/116398424278304767741/album/5...

I don't understand the electronics, but the logic is hidden inside the 9 volt battery connector.

The bit inside the 9 volt connector isn't really logic. The flip-flops and Schmitt trigger gates are just to generate square waves at 3 different frequencies. There's also a small power supply to drop the 9V down to 6.2V for the input of that, some comparators, and a bit of filtering.

The LEDs contain LC filters, tuned such that they'll light (visibly) when the appropriate frequency is applied. Touching the wire in different places creates a different parasitic load, which is detected by one of the comparators. That comparator then toggles the clock generator for the appropriate frequency, turning that LED off or on.

As with all of his circuits it's a brilliantly simple idea implemented in a ridiculously constrained space.

What I like is how it breaks down the model that most people had. Models simplify, but they also constrain and we need to always be cognizant of where the model stops.

Some people over train in model-space and are unable to make thoughts that occur outside of that universe.

This video of "Inside the RFID Stickers from a Chinese Cashier-less Store" (around 9:20 and again at 12:20) was a real eye-opener to me: https://www.youtube.com/watch?v=0QKrHi-G9WQ

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