For pictures, video clips and more, take a look in the ‘archives’ section and peruse older posts.

Introduction

The point source pixel system was designed in 2008 to be bright, easily chained and easy to use.  To that end, we settled on a system comprised of driver boards, a ribbon cable wiring harness, and small circuit boards containing the RGB LED and appropriate DMX reception hardware.

Each pixel includes a standard RS-485 receiver and a small microcontroller.  The receiver chip converts a balanced differential signal into a standard logic level that the processor can understand.  Each pixel requires three consecutive DMX channels: one each for red, green and blue.  Red is always the first channel, green the second and blue the third.

Of course, the start address of each pixel can be set to any number between [1 510].  Thus, 170 pixels can be discretely controlled by a single DMX universe.

Pinout / Wiring Data for DMX Splitter / Driver

A driver board has headers for  power  and DMX in/through.  It contains an RS485 receiver chip and 2 RS485 transmitter chips.  Since RS485 is meant to be used in shielded, twisted pair cables (rather than ribbon cable) we decided it made most sense to drive moderately short (10′  - 20′ long) cables.  If the ribbon cable is much longer, signal integrity of the high-speed DMX data is compromised.

Thus, up to 32 driver boards may be daisy chained together.  Each driver board has two outputs.  Each output can drive between 1 and 32 RGB pixels.

The system’s backplane is based on regular 10-conductor ribbon cable.  Since these are very light cable gauges, we use 4 conductors each for power and ground.  The remaining pair transmits the DMX data.

To build the backplane, we installed 10 conductor IDC female connectors at regular points along the ribbon cable.  Spacing between 6″ and 8″ seems to work well.

Point Source Pixels have a 10-pin male header, which conveniently attaches to the ribbon cable backplane.  Naturally, the header pinout matches that of the splitter / driver boards.

Sample part numbers from www.jameco.com:

• 10 pin male header #67821, $0.21 @ qty 10 (included on assembled circuit board)
• 10 pin female IDC socket #32492, $0.25 @ qty 10
• 10 conductor ribbon cable #643815, $15.18 / 100′

System Power

Each pixel has a built-in voltage regulator which converts Vin (usually 8-12V DC) to +5v required by the processor and LED.  Note that the RGB LED is driven from the processor’s pins.  This means that the board input voltage can vary somewhat, so long as it is high enough that the voltage regulator can function properly.  We’ve had spectacular success using switching power supplies designed for / removed from computers.  They output +12v DC at many, many amps, and for a very reasonable price.  Try www.weirdstuff.com if you don’t have anything lying around.  At full power, each pixel draws just over 60 mA at 5 volts.  A bit of Ohm’s law shows that

• .06 A * 5V = .3W
• 12V / .3W =  40 mA drawn from a +12v supply.

So choose a properly sized power supply for the job.

Wiring Diagram for Point Source Pixel

DMX Addressing

Naturally, for most effective operation each pixel requires a unique DMX address.

Since each board is too small to contain a DIP switch or display + pushbuttons, there are two ways a pixels DMX start address can be set.

1. In firmware at compile time.  Using a PIC programer and Microchip’s MPLAB, each pixel’s start address can be hard-coded into program memory.  This works well (we’ve done it thousands of times) but gets tedious after a while.  Also, a special programming harness is required to access the proper pins on the chip.
2. With an external programmer.  We designed the firmware to listen for a specific sequence of data, beginning with a ‘non-zero’ start code.  This start code / data sequence would never occur in a regular lighting system.  Think of it as a secret knock on the pixel’s back door.  When the proper data and checksum is received, the start address is stored in the processor’s permanent memory.  Changing addresses is easy and takes only a few seconds and can be done without any special computer programs.  See this link for a description and video clip of the field programming system.

That’s a decent overview of the system.  Questions?  What have we missed?  Send an email to john AT response-box.com.

It used to be that we’d write the pixel’s DMX address in firmware, then compile and program each PIC.  It worked well but got tedious.

Several thousand pixels later, we’ve got field-programmable source code up and running.

Short version: the PIC listens for an alternate (non-zero, dimmer data always is zero) start code in the DMX stream.  That start code is followed by a special packet of data which contains, among other things, the new start address plus a checksum.  The chances of this particular packet occurring naturally in your lighting rig are one the order of 1 in 2^80.  That’s a 1 followed by 24 zeros.  At the time of this writing, this number is slightly higher than the new US national debt.

‘Programming’ packets can be sent at any time.

The new address is, of course, stored in the processor’s permanent memory.

The address is also displayed by the pixel on power-up. The red LED flashes once (.2 S duration) for each ‘hundred’ in the pixel’s address or once (.6 S duration) if there are no hundreds.

Likewise for green / tens and blue / ones.

Channel 1 = long | long | short

Channel 12 = long | short | short short

Channel 304 = short short short | long | short short short short

etc.

So now, all pixels can be factory programmed with the same firmware.  This saves us a tremendous amount of time.

Firmware works for point source, ‘mini’ and ‘classic’ pixels and is totally backwards-compatible with anything we’ve ever shipped.  It will also work in 3-channel mode on the through-hole DIY pixels.  Haven’t had time to mess with the 5-channel version.

Contact us for a .hex file if you want to re-burn your own pixels.  Or send ‘em back and we’ll be happy to re-flash them with this new code.  Programmers are $46 and will be available soon in the online store.

Watch it work in the clip below. Click the arrows in the bottom right corner of the video frame for a full-screen version.

Setting Pixel Addresses in the Field from Engineering Solutions Inc on Vimeo.”>

Boring technical bits:

A normal DMX packet looks something like this on a ‘scope:

BREAK 0 X X X X X X X

Where 0 is the start code, which is then followed by between 1 and 512 8-bit channel values.

Our pixel programming packets have 11 bytes and look like this:

BREAK P I X E L S HH LL CHECK 0xFF

‘P’ is the upper-case ASCII character having a hex value of 0×50. ‘I’ is 0×49, etc. HH is the high byte of the new address. LL is the low byte of the new address. CHECK is the 8-bit sum of the high and low address bytes, overflow ignored.

Programming packets which don’t precisely match this format are rejected.

The pixel firmware doesn’t currently error-check the new address, so values between 513 and 65535 are technically valid. They’ll just never light up in any production lighting rig. However, the programmer firmware is range limited to [1 510]. What good would it do to park a 3-channel pixel at 512?

So I’m working on some new ideas for the 2009 Christmas season.  To get everything R&D’d I need to free up some capital.  And though my wife thinks I’m crazy, I’ve decided to sell the entire rig used for the 2008 build.

At its most basic level, the system includes

• 200 Point Source pixels, assembled and tested & guaranteed to run.

These little friends have been selling briskly in our online store at $7.50 each.  By my calculations, that prices the bare pixels – wiring, connectors and programming time excluded – at $1,500.

However, I’m reluctant to break up the system.  So to sweeten the deal, I’ve decided to add the following bits and pieces:

• One Isolated DMX splitter with XLR-5 ‘in’ and ‘through’ jacks, plus 8 output drivers and custom wiring harness tails.  These have been selling well for about $80 each.
• One Isolated DMX splitter with XLR-5 ‘in’ and ‘through’ jacks, plus 4 output drivers and custom wiring harness tails (my rig used two DMX universes, hence the double splitters).  Retail price is $60.
• 6 Data /  Power cable harnesses, each measuring between 80′ and 160′ long.  I paid $0.60 per foot for the two types of wire, plus about $4 for the polarized, locking Molex connectors on either end.  Total wiring harness length is very close to 600′.
• 6 DMX Splitter / Ribbon cable feed boards.  These convert connect the power cable harness to the ribbon cable runs and ensure that power and data are cleanly distributed.  They probably cost $15 each to build and test. 
• 6 sets of ribbon cable with connectors mounted on 8″ centers.  Each cable contains between 10 and 42 point source pixels.
• One +12v @ 12A switching power supply – more than beefy enough to run the entire system – with custom wiring harness pigtails.  Cost me $30 at www.weirdstuff.com a few years back.

Plus…

• I’ll re-flash each of the pixels with our brand-new firmware.  It will take about 3 hours, but I think it’s worth it.  The new firmware allows the a pixel to be re-addressed in the field – without using a computer.  It also boasts a 150 Hz refresh rate on the dimming routine.  This is 50% faster than the current firmware allows, and it makes fades and chases even more smooth.

And…

• I’ll throw in a brand-new hand-held pixel Programmer / Tester module.  It contains a tiny LCD plus several pushbuttons for easy navigation.  Setting and confirming a pixel’s address takes only a few seconds.  Once I get these assembled in bulk, they’ll be priced at $48 in our online store.  

So when the dust settles, this is a complete, ready-to-install RGB lighting package.  Everything is included and easy to configure.  You just provide a stable source of DMX and some imagination.

The system is guaranteed to arrive in working condition.  Your purchase also includes unlimited tech support via email, plus 5 hours of live, on-the-phone troubleshooting if you get stuck for any reason at all.

If I add up the prices of everything listed above, the total very nearly reaches $2,150.

However, I’ve decided to let it go for $1,839.  

I have to move quickly because our accountant will be very, very irked if he finds out what I’m up to.  

You should move quickly because things for sale here often don’t last long.  In fact, I’ve already emailed everyone who is a member of our exclusive ‘Insider’s Club’ (you can join at the top right corner of this page) and fully expect that one of them will swoop in and grab the gear at an incredible discount. 

So if you’re interested or have more questions, send me an email and we’ll talk.  Address is ‘john AT response-box.com’

* Note that there’s still some snow on the roof here, and I’m not going up to retrieve the high bits until everything is bare and dry.  It shouldn’t take more than another week if the current weather trends hold.

Below are a couple photos which show the wiring harness and ribbon cable adapters in more detail.  Click a photo for more.

I’m selling one  ’test’ string of point source pixels.  These are assembled and fully functional and have otherwise never been used.

The 25 pixels are mounted on 8″ centers on 10-position ribbon cable.  Since each pixel has a 10 pin male header, the cable can be easily and inexpensively replaced if desired.  Note that this is the same pixel spacing I used on the house this year.

Included in this package are the following:

• 25 x 10mm Point Source Pixels
• Ribbon cable with female headers on 8″ centers
• Ultra-tiny DMX splitter and power combiner module
• 5 pin male XLR connector for DMX input
• 2 wire leads for power input.  Power supply is +12V, tightly regulated.  For full brightness, plan on ~ 70 mA per pixel total.  NO power supply is provided.
• System guaranteed to arrive in working order.
• BONUS: Unlimited tech support via email
• BONUS: Up to 1 hour free tech support via telephone

Note that presently only 1 system is available for sale.

Pixels are programmed to DMX addresses [76,77,78], [79,80,81], … [145,146,147] respectively.  I’ll reprogram them to any other range for an additional $15.

Price is $179 + freight.  First come, first serve.  Send an email to john AT response-box.com with ‘I want the Pixel String’ in the subject line.  All major credit cards are accepted, and international shipping is no problem.

Pictures:

Point Source Pixels from John Chapman on Vimeo.

Point Source Pixels – Zoomed In from John Chapman on Vimeo.

I finished and tested a second 8-way DMX splitter, because the upper and lower runs are assigned to separate universes.  Then, I weathersealed the remaining 100 or so pixels for the three upper runs.  

We started installing at 5:30 and were finished a few hours later.

The test pattern we ran during installation – and which is shown below – toggles between green with red sparkles, red with green sparkles and blue with white sparkles.

All told there are about 200 point source pixels and 19 ‘classic’ pixels mounted in the garden lanterns.

Click a photo once for medium size, then a second time to see in a larger size.

Will post video clips once I’ve found a 3-CCD camera that has decent dynamic range.

The low parts of the house are done.  The high parts of the house are terrifyingly out of reach.  Will work on those later this week.

There are 100 point source and 19 standard pixels in the garden lanterns installed so far.  That makes 357 channels of DMX-512.

Click a photo one for medium size enlargement, then a second time to see it full size.