LED Tape (WS2812b) System Design - Thoughts and ideas appreciated

[empyfree]

Good morning all.

 

I'm making my first foray into using LED pixel tape, and hope to avoid rookie errors by doing my research first. I've seen lots of videos and "how to" type instructions and have pieced together an amount of knowledge.

 

Fundamentally I'm wanting to create a flexible system of LED control, to allow for my initial project (towards the end of September) but then to be useful in the future also. I don't mind treating the tape itself as a consumable, but the finished product of control and power supply needs to be solid and roadworthy.

 

I've made an initial plan based on using an Artnet Pixel controller from SmartShow. (https://www.ebay.co.uk/itm/SmartShow-NetPixel-Quad-16-Universe-Pixel-Driver-4-output-ArtNet-SPI-/273194230852)

 

(larger PDF version here: http://av-matrix.online/pixel-tape-designV1

 

My immediate plan is to get the controller, one PSU and a couple of lengths of tape to create a test-bench version of the above. It won't have the fancy enclosures or connectors to start with.

 

I know it's a lot of "plan" to take in at first glance! Any sage advice, warning, do's or don't's will all be gladly received.

[timsabre]

You will need to feed the power again at the 5m point. On all the tape I've used the colours go funny after 5m due to voltage drop.

[empyfree]

You will need to feed the power again at the 5m point. On all the tape I've used the colours go funny after 5m due to voltage drop.

I was afraid this might be a (sensible) suggestion.

 

I'll re-design to keep the power and data separate right to the point of joining the tape then, having a couple of power outlets per "power injector" enclosure and only daisy chaining the data.

[pmiller056]

The 30A fuse on the PSU output will never blow. The power supply will not produce enough fault current to make it operate as intended. Large currents and voltage drop on the 5V system WILL be big problems to making it work. If there is any significant length of 5V power wiring the cable will need to be very thick (minimise voltage drop) to make the system work correctly. As noted above, for long runs of tape you will need to feed power in at multiple points.

 

The LED tape is fairly fragile and is easily damaged by poor handling or repeated flexing. The LED tape will become noticably warm in use, (but not dangereously so if in free air or on a timber surface) causing it to expand along its length. The heat also softens the glue on the backing. This will cause long runs of tape to come away from the surface it has been stuck to, particularly non metallic surfaces.

 

The LED control signal is a TTL level signal at around 800kHz, so it will not go any significant distance before it becomes unusably distorted. The control input to the LED strip is a static sensitive logic gate input and probably will not survive for long with random bits of wire directly hanging off it. (Or being connected to the system before the power is connected). Consider converting the control signal to RS485 or similar at the master station and a suitable receiver at the start of each strip.

 

[empyfree]

Cheers Pmiller056.

 

I figured there must be a way around extending the control signal, having the controllers centrally located must be preferable in a lot of installations? I'll look into the RS485 converters you mention, I'll also investigate this solution that I spotted while trawling youtube!

 

As Tim pointed out above I need to split the power into smaller chunks to keep the power drop to a minimum. I have no issue running chunky flex up to the tape. Split in half I'll be looking at a theoretical max of 15A draw per line, so 1.5mm H07 should cope with the current. From your experience is it simply not worth having fuse protection on the tape side of the PSU? or just go for a much lower rating?

[timsabre]

The 800khz control signal will travel quite a long way (10s of metres). You should not need to convert it to rs485. You can blow up the data input to the first led on the tape but just cut it off and start with the 2nd one.

 

What can be a problem with long runs of tape is the ground voltage gradually rises up due to volt drop. When you refeed the power this can muck up the logic levels and the 2nd run of tape can be unreliable.

 

Pmiller is right about the fuse, the psu will just go into protect before it blows if you put a dead short on. However you can make lots of smoke and possibly fire if you get a low resistance across the psu.

[empyfree]

What can be a problem with long runs of tape is the ground voltage gradually rises up due to volt drop. When you refeed the power this can muck up the logic levels and the 2nd run of tape can be unreliable.

 

Would feeding the power in from both ends mitigate this?

 

 

Pmiller is right about the fuse, the psu will just go into protect before it blows if you put a dead short on. However you can make lots of smoke and possibly fire if you get a low resistance across the psu.

 

What can be done to protect things?

[timsabre]

What can be a problem with long runs of tape is the ground voltage gradually rises up due to volt drop. When you refeed the power this can muck up the logic levels and the 2nd run of tape can be unreliable.

Would feeding the power in from both ends mitigate this?

Might do. It's a problem I've only come across a few times. The other fun problem is if you have tape on a metal structure it's quite easy to get a connection from the tape onto the metalwork, either the 5V or the ground. That can cause some unexpected behaviour.

 

Pmiller is right about the fuse, the psu will just go into protect before it blows if you put a dead short on. However you can make lots of smoke and possibly fire if you get a low resistance across the psu.

 

What can be done to protect things?

All you can do is break it down into smaller chunks with smaller power supplies. I am always a bit nervous using large power supplies like that as there is the potential to create a lot of heat in a fault situation. E.g. if you get a short near the end of a 5m tape the PSU might keep driving into the tape since the power tracks are relatively thin and there's quite a bit of resistance. The tape will get very hot but the PSU will just keep on going.

 

[musht]

Dunno if you gain much splitting the control into a separate box with PSU, input to that is ethernet with some error correction, output through couple more links is TTL stream.

 

Own feeling is 5V pixels great for wearable and wireless where can use a USB bank as power source.

 

WS2813 or WS2815 (4 pin, back up data line) 12V pixels make current more manageable on install, still power inject both ends at 5m.

 

Vid you linked is Mr Smartshow Bobby. Differential allows isolating ground issues over distance or going the full, buck/boost, PoE route , stuff 70W down a Cat5 line.

 

Make sure its a rigid backed connection to end of tape with glue filled heatshrink and cable ties for the plug tail.

 

Tape on fabric , dinnae , its the solder joints that crack up with the flexing, rigid LED boards joined by mega flexible test lead cable.

 

Look at PTCs for protection

Edited July 29, 2019 by musht

[pmiller056]

From BS7671, two core rubber insulated 1.5mm2 copper wire will have a voltage drop of 31mV/A/m. The thermal limit (conductor temperature rise to 90C) is about 24A lying open on a floor from the same information. So 5m of 1.5mm HO7 operating at 15A will get warm and drop 2.3V along its length - not relevant when working with mains operated stage lighting, but it will stop this project from working. Don't forget that the intended load for your chosen PSU is 125mOhm (ie 5V@40A), which for most uses near enough a short circuit and as noted above, it is unlikely to notice the difference between the intended load and a fault and keep going regardless.

 

You will start off with a good data signal from the sender, but this signal must still have the correct relationship to LED ground at the LED - with power voltage drops this may not be the case. To improve relability you will need to put some kind of ESD/spike protection or buffer at the LED and probably the sender. Randomly plugged in data lines straight into the LEDs is asking for destroyed parts and it's not always desireable to have to chop the first LED off yet agian....

 

[ed_ld]

I use the Enttec pixel range quite a lot and find it pretty bomb proof. They have 12v tape which is great for long runs without voltage drop. It also feels thicker with better tracks if you're flexing it quite a bit.

They also have quite a nice system with their Pixelator as a central control hub and then P-Sats as power supplies that branch off it to be near each piece of tape.

Perhaps a bit more pricey but very robust and scaleable to the size you need with the pixelator mini for smaller projects.

Everything is on powercon and 4-pin Xlr. I buy mine from White Light for a fairly competitive price.

 

Maybe worth a look if you haven't already?