An LED bulb with integrated controller chip

Reverse-Engineering A Two-Wire LED Strip Protocol

Although Christmas may be several weeks behind us, various colorful LED contraptions can nowadays be found in our houses at any time of year. [Tim] got his hands on an LED curtain that came with a remote control that allows the user to set not only the color of the LEDs as a whole but also to run simple animations. But these were not your standard WS2812B strips with data lines: all the LEDs were simply connected in parallel with just two wires, so how was this even possible?

An oscilloscope screenshot showing the data protocol used in an LED string
The LED string protocol is very simple, with one address field and one data field.

[Tim] hooked up his oscilloscope to the LED strings to find out how they worked, detailing the results in a comprehensive blog post. As it turns out, the controller briefly shorts the LED strip’s supply voltage to generate data bits, similar to the way old pulse-dialing phones worked. A tiny chip integrated into each LED picks up these pulses, but retains its internal state thanks to a capacitor that keeps the chip powered when the supply line goes low.

After reverse-engineering the protocol, [Tim] went on to implement a similar design using an ATMega328P as a controller and an ATtiny10 as the LED driver. With just a few lines of code and a 100 nF buffer capacitor across the ATtiny’s power pins, [Tim] was able to turn an LED on and off by sending pulses through the supply lines. Some work still needs to be done to fully implement a protocol as used in the LED strings, but as a proof-of-concept it shows that this kind of power-line communication is possible with standard components.

We’ve seen projects that send signals down a two-wire LED chain before, although as an add-on to a more ordinary LED strip. [Tim] is not the first to reverse-engineer poorly documented LED strip protocols, but probably won’t be the last either.

Decabit: Or The Conspiracy Theory That Wasn’t

[LDX] first noticed the odd sounds coming out of his ceiling fan, regularly, on the hour and half-hour. Then he noticed that the lights were flickering as well. Figuring something was up, he built a logging power-line monitor to see if he could decode the shadowy signals and figure out what cryptic messages were being transmitted over the power lines. Naturally, he suspected the Illuminati were behind it.

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Reverse Engineering An AC Signal Protocol

[Arpad] has spent quite a bit of time reverse-engineering a home automation system, and, as he is quick to point out, presents the information learned for informational purposes only. He’s really done his homework (and documented it well), looking into the US patent application, and figuring out how the protocol works.

If you’re wondering how someone is able to send a signal over an AC sine wave, at least one technique is the proprietary [Universal Powerline Bus]. This works by sending precisely times pulses in conjunction with the wave that would exist normally. Given the correct software on the other end, this can then be decoded and used for whatever data transfer is necessary.

Although as engineers and technologists, we certainly don’t condone stealing patents,  part of point of one is that others are allowed to learn your secrets in exchange for some legal protection. [Arpad]’s motivation in doing this is that the technology is only widely available in the US with our puny 120 VAC 60Hz power. With this knowledge, he’s been able to transfer it to work with European 230 VAC 50Hz.

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