2009 RGB Micro Pixel

Two days ago the FedEx fairy delivered our first factory-assembled batch of Micro Pixels.

I unwrapped a handful, snapped a couple pictures, then plugged them in on the workbench.

Nothing happened.

Double checked the board layout against my schematic and the controller’s datasheet. The trusty ‘scope showed that all the signals were in their proper places.  And the control program was the same one I’d used when testing the rough system prototype a few weeks back.

Bizarre.  Potentially very expensive.

After another hour of testing, I discovered that the sample LEDs from the factory were different than the production LEDs.  Each had six pins and looked identical to the eyeball.  But a diode tester revealed that the polarity of all three LEDs was reversed 180 degrees.

+ + +

- - -

vs

- - -

+ + +

Turns out the LED factory had switched things around but not updated the datasheet on their website.

Oops.

Good that this was a test run of 100 pieces, instead of production assembly in multiples of 1500.

I used hot air to remove the three LEDs, then spun them around and re-attached.

At full power, these chips are exceptionally bright. They leave ghostly spots on my eyeballs.

Before running out of time that afternoon, I reworked three of the boards and chained them together.  Everything operated flawlessly.

I love the simplicity of this new design.

P.S.  We’ve had a suggestion for a new name for these guys:

Tripix

3 LEDs, 3 Colors, price approaches the $3 range in large quantities.

What do you think?

(Note: There’s some additional discussion on the controller design in the ‘comments’ section below.  So click there to learn more.)

Just before shipping the order to me, the factory took a couple of ugly pictures of the new circuit boards.

It looks like the shipment of 100 boards will arrive later this week, barring problems in customs or a volcano eruption in the parcel’s flight path.

Visible are 2 x RJ45 jacks for easy daisy chaining (I found a supplier who will sell 6″ cat5 jumper cables for $0.48 each in small quantities).  The rear of the board contains 3 x wide-angle RGB LEDs wired in series.

Note the the component count of this design is significantly lower than anything we’ve done in the past.

For lack of a better name, this design has been yclept “The Micro Pixel.”

If you missed the introduction to the 2009 project, you can find it here:

http://response-box.com/rgb/2009/06/2009-rgb-pixel-project/

More soon.

This post attempts to gather all of the important Point Source Pixel information in one area.  Click on any picture below to enlarge.

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.

Hard to believe that four years have passed since the first DMX RGB Pixel Project was cobbled together.

For 2009, we’re working on something completely different.  These don’t yet have a name – or even some sample photos – but here’s a sneak peak of the feature list.

• System brightness to be halfway between the point source and a ‘classic’ big pixels.  Design uses 3 each wide-angle red, green and blue emitters.
• Component count is *significantly* lower than any of our existing designs and 100% surface mount, which keeps the assembly robots fast & happy.
• Boards are daisy chainable with cat5 jumpers OR hard-soldered connections, up to 255 per string, provided that +12v supply is re-injected from time to time.  Current draw remains stable at ~ 60 mA per pixel.
• Position Agnostic!  No need to address each individual pixel.
• Head-end controller handles all DMX massaging, addressing and color updating.
• Working on a plastic ‘overmolded’ enclosure for a totally weatherproof system.
• May even feature a plastic ‘jewel’ similar in size/shape to a standard C9 lamp.
• Circuit board size is 2″ x .6″
• Head-end controllers will be daisy-chainable using industry-standard  XLR-4 ‘Color Scroller‘ cables, which combine a shielded, twisted pair for data and a heavy gauge pair for power.  Last year’s cable harnesses (1 x cat5, 1 x 18 gauge pair) worked well but took way too long to assemble.

I’m very excited about these, actually.  The assembly shop is working on a test batch of 100 pieces, which should be delivered in a week or so.

Pictures & video clips to be posted as they’re available.  To be kept abreast of the latest developments, join the ‘Insiders Club’ at the top right corner of this screen.

This is a second revision of the DIY pixels we’ve been selling for the past year or two.

Notable changes:

• Support for field addressing per SRM’s jumper code, which is discussed in further detail in the DIY Christmas DMX Section.
• Nifty white soldermask.  Good for reflecting LED light back toward the eyeball.

There was some decent interest in a completely through-hole design. Some folks wanted to build their own pixels but weren’t comfortable with surface mount components.

This board receives DMX through a pair of RJ45 connectors in parallel. A SN75176 translates the differential data into a single-ended signal that the PIC can process. 5 x 2N3904 transistors drive 5 banks of LEDs.  The intention was to drive red, green, blue, amber and white LEDs.

The LEDs are arrayed as follows:

R G B W A R
G B W A R G
B W A R G B
W A R G B W 
A R G B W A

Useful PDF Files:

• Bill of Materials
• Schematic
• Loading Diagram

I currently have about 70 of these boards for sale.  $3.50 each or 10 for $28.  Send an email to John AT response-box.com if you’re interested.

Sorry, all boards have been spoken for.  We can certainly order more if there’s interest.