Here be Dragons:
This project assumes a reasonable knowledge of electronics and computer-based light control. These pixels may or may not be suitable for your particular application.
In fact, they may not be suitable for any application at all. Know that we've done our best to present a stable, well-engineered design. But we're not responsible if you, your house, your theatre, or your dance club start on fire.
Please proceed accordingly.
What type of power supply do I need?
Without any question, you need a tightly regulated +12V DC switching power supply. The pixel design has the LEDs connected directly to this supply. So using an unregulated power source could seriously anger the LEDs.
Each pixel draws about 130 mA at peak brightness. So size your power supply accordingly. Peak brightness is not white, by the way. It's a bit blueish. But it is possible to create some great shades of white.
Jameco sells many, many options. I've also had great luck using surplus computer power supplies. Try www.weirdstuff.com for great prices. And this link will walk you through the conversion process.
Which cable should I use to connect the pixels?
Regular CAT5 jumpers. We've been very pleased with purchases made from www.showmecables.com. You need a 'straight through' cable, not a crossover cable. Or build your own. Just make sure the wiring follows an accepted standard.
Of the 8 conductors in a cable, this design uses three each for power and ground, plus a twisted pair for data. However, the wiring scheme does *not* conform to any published standard (USITT or otherwise).
THIS IS NOT ETHERNET!
DO NOT MIX YOUR NETWORKING GEAR WITH YOUR RIG OF PIXELS!
If you connect the CAT5 output of your shiny new Hog directly to a pixel, Bad Things will happen.
If you connect a string of pixels to a regular networking switch or router, Bad Things will happen.
The only commanality between the two systems is the cable and connector.
In the store section of this website you'll see that we sell small circuit boards which merge DMX and power into a single CAT5 cable. They aren't required, but it does make the installation process go a bit faster.
Thus, if you connect the DMX output from your shiny new Hog to a string of pixels using one of these 'merging' circuit boards and a proper power supply, you'll be delighted at the system's brightness and ease of control.
How many Pixels can I string together?
Technically, 32 per DMX DMX driver / optosplitter output.
However, field tests have proven that if more than about 20 pixels are connected together and driven at full brightness, the resistance / voltage drop of the CAT5 cable becomes significant.
The solution is to 'double power' longer strings of pixels. Connect the +12v supply to each end of the chain, then add data to only one end. You should have no problems.
The pixels use a bog-standard SN75176 RS-485 receiver. Yes, there are other receiver chips out there, and some of them place such a small load on the line that 256 can be used simultaneously. But, their cost per chip was an order of magnitude higher. Sorry.
What's the Pixel's refresh rate?
Just under 100 Hz. Also, full speed DMX input (44 frames per second) is handled with ease.
Any color correction?
Nope. 8 bits in, 8 bits out.
How do I set the pixel's start address?
Here's how it works: at programming time in our shop, every pixel gets a default address of '1'.
The pixels respond to two specific DMX packets, Packets with a 'zero' start code (signifying dimmer data) are treated normally and the R, G, and B LEDs are controlled appropriately. Channel N is red, N+1 is green and N+2 is blue if you're using the 3-channel firmware.
Packets with a specific *non-zero* start code (for safety, these packets are repeated several times in a row) contain data for re-setting the DMX address *and* switching back and forth between 3-channel and 4-channel (intensity, R, G & B) operation.
This configuration data is stored in the chip's EEPROM and can be changed at any time.
It's a bit like a secret knock at the treehouse door. It the PIC hears the right one, the door is opened and the furniture can be re-arranged.
Also, on startup the pixel's LEDs will flash in a specific pattern representing the start address.
Shortly, we'll post details of a 'programmer' circuit board.
It contains an 8x2 LCD display, a few pushbuttons and connectors of the proper flavour. It will either send out (a) a full standard DMX packet for testing your lighting rig or (b) the special 'door knocking' packet for changing a pixel's start address.
If you'd like a stack of pixels and don't anticipate changing their addresses, let us know and we'll set them here in the shop. Then you don't need to worry about reprogramming.
Are these Pixels hacker friendly?
Absolutely! In fact, that's a big part of the project. Each pixel contains a 16F688 microprocesor and a 5-pin programming header (+5v, Gnd, Vpp, Pclk & PData). The chip has 4K of memory and we're only using a tiny chunk of it. So feel free to edit and change to your heart's desire.
Naturally, you'll need a PIC programmer and complier of some sort.
If you come up with something cool, let us know.