By now, most people in the church production world would be familiar with LED Tape – multi-coloured LED chips soldered onto a lightweight, flexible PCB backing – able to be stuck in all sorts of areas with adhesive. Traditional LED Tape only allows one colour per segment.
LED Pixel Tape, on the other hand, allow you to control each LED individually via a special control protocol. This article introduces you to Pixel Tape, and explains some of the basics you need to get started.
You can think of Pixel Tape as a very low-resolution LED Video Screen, but controlled via DMX instead of SDI or HDMI.
I’ve only started purchasing Pixel Tape at the start of this year, and when I was researching the best products to buy I was struck by the lack of information online. Enttec have the best guides (they actually manufacture LED Pixel Tape in Melbourne, which is super cool!), but after that it’s a bit hard to find much else. The online stores are as bad as each other, often posting inconsistent and contradictory product descriptions!
First, let’s break down the basic components in any LED Pixel Tube system:
- Pixel Tape
- DMX to SPI Decoder
- Power Supply
- DMX Source (Console, Media Server, etc.)
Pixel Tape has LED chips soldered on to the lightweight tube, but it also has SPI Decoder chips (normal LED Tape doesn’t have these decoders). These chips receive a control signal (SPI), and in turn control their individual LED. They then pass the signal onto the next chip, which decodes the next piece of information.
There are many types of SPI chips, such as:
All of these behave in a similar manner, and many decoders support the full range of chips, but you need to be careful to make sure everything matches when purchasing.
Where to buy LED Pixel Tape from?
Enttec have the best supply of ready-made LED Pixel Tape products, but be prepared to pay a premium. I did a lot of research and talked to a lot of suppliers, and eventually purchased my Pixel Tubes from Alibaba – settling on the supplier Shenzhen Shiji Lighting Co.
The whole marketplace constantly changes, making it hard to recommend a long-term supplier on Alibaba or eBay. However, for a point of reference, I purchased the following parts:
- SJ-A10060- 2903 – 20mm tube diameter, SMD 5050 RGB LED, 60 LEDs/m, 10 pixels/m, UCS2903 SPI Chip, DC12V, 14.4W/m, 1m tube
- SJ-DMX-SPI – DMX 512 Decoder, 3W, 170 pixels, DC12-24V
- Various 3-pin cable (most of this stuff uses tiny 3-pin connectors to carry signal & power)
I then locally purchased 12V 72W power supplies (Mean Well LRS-75-12), plastic jiffy box, connectors/plugs, sACN to DMX node, etc.
If you don’t know anything about soldering, voltage drop, etc. – then I suggest purchasing a pre-built solution. However, if you have some time and are handy with some tools, let’s dive-in and get started.
I personally opted for pre-made tubes over cheaper tape on rolls, as it made my life a lot easier by removing assembly. I’ve wasted a lot of time in the past soldering up LED Tape – and I’m keen to avoid doing that again whenever possible! The only assembly was for power supplies & Decoder cabling.
DMX Control & SPI
DMX is still the de-facto protocol used to control these sorts of LED products. I used Resolume Arena 6 to generate the DMX (via sACN/ArtNet), and DMXKing sACN Nodes to convert this to ordinary DMX512. Then, I used a DMX to SPI interface/decoder from my Alibaba supplier to make the conversation into the correct protocol for the lights.
You could use a lighting console to do the control, but you will eat up a lot of channels very fast – and depending on the type of effects you want to achieve, it may be quite hard to setup. Resolume (and other media servers) makes it easy to use video content & textures to map across the tubes, and it provides a sACN & DMX output which can be converted to DMX512. Some people also prefer use MadMapper, especially if you’re dealing with a larger quantity of tubes.
DMX supports 512 channels per-universe. We need to do some math to work out how many Pixel Tubes we can control per-universe.
The LEDs in my tubes were RGB (3 channels), and there were 10 individual segments per-tube. This means we’re using 30 DMX channels per-tube. This allows for 17 tubes per-universe. For my particular design, I decided to run no more than 15 tubes per universe. When you read down below about the power and cabling requirements, you’ll see why.
The DMX/SPI interface basically has three connections we need to worry about:
- 12V Power In (+, -)
- DMX In (Shield, +, -)
- SPI Output (Common & Signal – ignore the Power & Clock outputs)
On my particular decoders, all of this comes on screw-terminals – so you need to wire up patch cables directly into the unit.
Power & Voltage Drop
Power is probably the most complex part of dealing with pixel tape. Each of my tubes consumes 14.4W. Across five tubes, this gives us 72W – the amount which can neatly fit on one of those Mean Well PSUs I mentioned earlier.
There is a temptation to purchase a bigger power supply. However, this is not recommended. After 5 tubes and a bit of intermediate patch-cabling, you start to suffer from voltage drop. This can manifest itself via discolouration in the last few LEDs on the last tube. It can also start to mess with the SPI Chips on the tubes, and kill your data signal.
Basically, I’ve wired up t-adapters to insert every 5 tubes to inject power. As it’s all DC, we can do this easily.
The manufacturer can supply the 3-pin cables in a ‘T’ arrangement, with a bare end for power. I found some robust 2-pin connectors at JayCar, and soldered these onto all my power cabling & adapters.
You also need to be careful not to have too much physical distance between the PSU, and the lights. This will contribute to voltage loss too. Keep that PSU as close as possible to the injection point.
How do you know if you’re suffering from voltage drop? The LED chips closest to the end of the chain will start to discolour, especially when you go 100% Red, Green & Blue. If the voltage loss is particularly bad, you’ll start to see flickering LED chips, and possibly even dead pixels. If the voltage gets too low, the SPI chips won’t work and the data can’t be passed through to the next chip (even if you re-inject power).
This diagram shows the basic connections for 10 LED Pixel Tubes, with one DMX Decoder, and two power supplies:
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