Has anyone reverse engineered how LED curtain hooks work?

My theory is that the chip in the hook at the top of each strand works similar to to how each pixel in a WS281x works. It strips off a certain number of bits and sends them down the strand and then sends the rest of the data down to the next hook. I also figure you must be able to configure how many bits it sends down the strand vs passes along to next hook.

I was talking to a Chinese manufacturer who said he’d sell me just the hooks. But the the image he sent was mostly in Chinese. It does look like each hook is numbered. So I may not be correct in how they work. I’d like to make custom sized curtains. If anyone knows of any documentation or reverse engineering in English I’d appreciate it.

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Tries Google Lens or Google Translate?

It is an image, I don’t know to run an image through Google translate. But we’re slowly working through the language barrier.

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Perfect. Thank you.

How did you go with this? I’m trying to get an LED curtain going that looks like this, and would be interested in the protocol details for the hooks, otherwise I’m going to have to crack open the logic analyser and start reverse engineering it.

Here’s what I’ve discovered so far:

  • Setting the strip as WS2812 only writes to the first string, regardless of the length
  • Setting the strip as APA106, and setting a very long length (>575 pixels) seems to overflow the chips in the tees, and causes a cascading wave of replicated data down the curtain, eventually causing the whole curtain to mirror the first segment. This can be confirmed by creating a 20 pixel segment, and another segment for the rest. Run an effect on the first segment, and turn the second segment off, and each column mirrors the first.

Here’s what is inside the tee:

Mine works as simple WS281x, but with RGB order instead of BRG. The hook just sends down one strand’s worth of data and passes on the rest.

Now there may be different variants.

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Thanks, did you ever crack one open? Does it look similar?

The SOT23-5 chip on the right appears to be one of these, or similar:

The chip on the left has had it’s markings blasted off, but is probably a microcontroller.

The VCC line of the buffer is connected to a uC pin, the input is connected to DI, and the output is connected to the downstream DO. This allows the uC to regenerate the signal and pass it down the line, after blanking however much it wants to keep.

For the LED strip connection, DO is connected directly to DI.

I’m not sure why they have the buffer there, I would have though the uC’s GPIO would be sufficient to regenerate the signal.

The chip on left could be a Padauk PMC150:

The VCC (2) and Ground (5) pins align with the datasheet.

I had not but I have now… and interestingly there’s nothing in there, just a parallel connection. No PCB or component anywhere.

So in my case it has to be the first LED of each strand that is programmed to specifically skip X data, similar to DMX strips…

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I hooked up a logic analyser to the original controller, and every 20 leds, I can clearly see a logic high pulse that is ~5uS long. This is out of spec for the LEDs, so they ignore it, but it’s pretty likely that this is the signal to tell the chips in the hook to direct the next data stream down to the next hook.

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Have you got any results ? i just bought some and i am stck at the same place. First row lighting but nothing on the line after.

So i got a 2m x 2m RGB adressable led curtain (like a govee one but cheaper). It have a little usb-bluetooth dongle and works with BLE low energy with an app called “LotusLamp X”.(https://www.aliexpress.com/item/1005006285161602.html?spm=a2g0o.order_list.order_list_main.5.19cd1802JDRBxi)

r/WLED - Aliexpress LED curtain - weird signal

BLE is named ELK-LAMPL with last bits of MAC (i assume)

r/WLED - Aliexpress LED curtain - weird signal

BLE Thingy cracked open.

It is 20 pixels by column. 20 columns in total. 400 leds / pixels. At each Y split connection from the master row to the column, there’s a chip which seems to take the first 20 adresses and output the rest to the next column.

r/WLED - Aliexpress LED curtain - weird signal

Dividers. This is the last so nothing is hooked to DO

I dug up a 8266 with Wled 15, plug that shit up to D4 annnnnnddd… Only the first row is ligthing.

Hook back up the BLE thingy, fire it up, works again in full.

What i tried so far :

  • 400 ohm Resistor inline on D4
  • Level shifter 3-5v

So i broke out the cheap USB osc. i got years ago and hook it up to each of them.

r/WLED - Aliexpress LED curtain - weird signal

Hooked up to the Data line at the output of the BLE

r/WLED - Aliexpress LED curtain - weird signal

Hooked up to the ESP8266 with WLED. Config : WS281x 400 leds

So clearly this is not looking to be the same communicaiton protocol. I tested it up with 2 different ESP8266.

So i’m at a loss here. Any other pointers i should check ?

So this sounds like you need to either (1) recreate the protocol on the controller, with a 5uS pulse every 20 leds, or (2) create a switch that copies Di to an output while counting 24*20 pulses and then switches the output from the string to the Do. I’m trying to do something like (2) and am having problems getting stable results probably because my chosen MCU (an ATtiny202) struggles to keep up, but I’m still working on it. Approach (1) seems easier to try and give up if it doesn’t work.

I am looking to recreate the protocol to add the 5us pulse but i don’t now where to start messing and testing in the wled codebase.

I’d presume that would be in the LED protocol library, FastLED (GitHub - FastLED/FastLED: The FastLED library for colored LED animation on Arduino. Please direct questions/requests for help to the FastLED Reddit community: http://fastled.io/r We'd like to use github "issues" just for tracking library bugs / enhancements.). Unfortunately, I am not very familiar with this library, and it seems a bit too big a codebase to figure out at a quick glance.
Then you’d need to figure out how you want to package and integrate your changes.