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New build - wires and cables
#1
Hey guys,

I'm looking at starting a project with my AllPixel that I'd like a bit of help with in terms of planning, and in particular with the amount of voltage and amps I can push through certain cables and wires.

What I'd like to build is multiple vertical led strips, free-hanging from the ceiling/down a wall, and then run a cable along the top linking them together.

Assuming I'm running the strips with data-in at the top and data-out at the bottom, my first thought is to solder a wire from the Data out pin and run it along the back of the strip so that I have it available at the top. Then I need to find a plug (or two plugs) to build into the top of the strip so that I can have power/data in, and power/data out. That will let me chain a series of strips together (and run them as a matrix with the AllPixel)

With a desire to use commonly available plugs/sockets, I only need three pins to link it up (5v+, data, 5v-). An idea might be to use 2x headphone socket (3.5"/3 pin) on each strip, one as input and one as output.

Given the LED strip I have (WS2812 / 5 metres), can I use regular old audio cable to wire up the strips, or is it too much voltage/amps for the cable? I am using a separate power supply for it, I think it's 2A off the top of my head (will check when I get home tonight.)
Is there a smarter plug/socket combination I should be thinking about?
What gauge wire can I use to run the data-out signal to the top of the strip?

Any help is greatly appreciated! This will be my holiday break project, looking forward to having the time to sit down and build it out (and code it up!)
Thanks!
#2
Hmm, interesting idea. How many "columns" are you planning? Would each one be 5m? Or would you chop the whole 5m strip into smaller segments? If so, how long would each segment be? The total length of LED strip used will help with some of the wire/power supply recommendations I make Smile

One advantage of the BiblioPixel library (if you plan on using it which we recommend Wink ) is that you can configure your matrix as a "serpentine" layout. This means that instead of each strip starting at the top of the matrix, they would alternate. I.E. you wouldn't have to run the data line back to the top of each one before jumping over. You could still power all from the top (length permitting), but you would only have to run the data line a short length across to either the bottom or top of the next strip. Then in code, you can define this configuration and the matrix should work as expected. (For Reference: https://github.com/ManiacalLabs/BiblioPixel/wiki/Display-Setup#coordinate-mapping)

Of course, if you'd prefer to hide all of the wires at the top, then you would need to run the data line back to the top. And this is where it gets tricky. The WS2812 LEDs use a tricky communications protocol that is very sensitive to timing. Having long data line runs between pixels could make the data line more susceptible to electrical noise and voltage dropoff. This may result in intermittent communication, which would result in the matrix not working right.

And this is why I asked about the specifics in terms of the number and length of the columns. If you can provide some more details (or at least what you're thinking in terms of measurements), I/we'd be happy to offer recommendations Smile

As for the connectors, I wouldn't recommend headphone plugs. The main reason is that, when you insert the plug, each contact has to slide across others before it is fully seated. It may not be an issue if you only connect/disconnect things when power is off, but it may be an issue when power is applied. You could short power to ground or power to data, which could damage the strips, your power supply, and/or your controller. Realistically, there probably wouldn't be much harm if you chose the contact ordering carefully, but it's not really a "Best Practice" thing to do.

Instead, I would recommend something like a 2- or 3-pin JST (or similar) connector: http://amzn.com/B013WTV270. Something like this ensures that you can only plug them together the correct way, and that no pins cross. Depending on your power draw, the gauge may or may not be adequate.

Speaking of adequate gauge, do you know the gauge of the cable you plan on using for power?

For the Data line, since it's only 5V logic, you can get away with a pretty small wire gauge, again, depending on the length of the run. I would say 22AWG to be on the safe side, but I wouldn't go smaller than 24AWG.

Hope that helps a little! Of course, we'd love to see pictures when it's up and running Smile When you come back with some of the details regarding the measurements, I'll see if anything I said would need to be modified.

Thanks!
#3
Thanks for your reply Dan. Already you've given me some things to think about.

I was planning on using the one 5m strip, cut into approximately 10-15 light strips. This means around 10 or so strips to cut and wire up. From memory my 5m spool has 159 lights on it.
There will be a ~30cm distance between each LED strip that a cable needs to run, and I would prefer to keep the wires along the top of the display. Also if I use plugs and sockets between each strip, I can change the layout of the whole piece at a later date easily (or add or remove strips...)

For the cable to connect the strips together, ideally I'd like to use 10x off-the-shelf cables (thus the idea of using a common plug for each strip), so I don't need to construct each cable. Still, it's not the end of the world if I have to cut my own cables.

Agree that shorting the cable with Audio plugs would be bad™. Happy to use a 3-pin JST connectors, if I can find some matching pre-made cables to use with it. Other (dumb) ideas of mine were using RJ12/45 plugs + Cat5, or USB sockets + off-shelf USB cables. If I do need to construct each power cable, what gauge should I be using?

How crazy is this plan? Greatly appreciate you taking the time to help shape my thinking for all this.

Thanks!

It may help you to know that I'm trying to plagiarise this art installation, but obviously with strips not as long (nor randomly laid out in the room.)

https://vimeo.com/44428571
#4
Not crazy at all! Very do-able, I'd say. Smile

You may even be able to get away with running the data line from the bottom of one strip to the top of the other. I would recommend testing this on a few sections before you get too far into the project. Maybe take two segments, power each, and run, say, a 80cm small-gauge wire between the data out on one and data in on the next. Try driving a pattern and see if the strips misbehave. Depending on how that test goes, you should have a better idea of the feasibility of running the longer data lines.

From a Power standpoint, I think you're in good shape as well. If you can find any of the pre-made JST connectors I mentioned earlier, those should work. You might even be able to find pre-made male/female pairs with enough wire on them to do what you're looking for with minimal extra construction. Overall, 22AWG should be OK for this, provided you're not driving full white at max brightness for several hours on end Wink

And I agree, it would be nice to be able to reconfigure the overall piece. The only thing to keep in mind is that if you add more segments, your power requirements will change, and you might need another power supply. You may find, depending on how the final construction performs, that it may be worth it to power half of the segments with one supply, and half with another (assuming you use 2A supplies). For this, your grounds on the two halves would need to be tied together, but the 5V+ would only connect to one half of the segments. DON'T connect both 5V+ lines together. This may damage your power supplies, among other bad things.

Hope that helps!


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