P-DMX 25 pixel (or 5 servo) controller with DC converter

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David_AVD

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This controller is now available. Further info to be found here




I have an idea for a low cost P-DMX pixel driver (with on-board step-down regulator), but it would be limited to 25 pixels, either 2801 or 6803 type.

You'd feed P-DMX (power + DMX over CAT5) to it. I was thinking a pair of RJ45 sockets (P-DMX loop in/out) and a single 4 way pixel connector. Maybe a DC power connector for those wanting to use regular DMX (no power) and a separate 24V DC power feed.

This board would step the 24V down to the 5V that the 2801 / 6803 pixels require. The regulator is good for 1.5 Amps, so that's the reason for the 25 pixel limit. (60mA x 25) Since the regulator is near the pixels, it would solve the typical voltage drop issues.

As for addressing and options, a DIP switch would be easiest, but adds cost. A little button to set the start address and pixel type could be used perhaps. That would save board space and a little money, but are people comfortable with setting options via DMX?

I don't have any firm idea on price yet, but at a guess it may be say $30 as a fully built board?

What sort of display elements could you make with 25 x pixels? Arches, small 2D tree outlines.... ??

Anyway, what are your thoughts on this? Sound interesting? Dead dog? Other thoughts? Over to you. :)
 

lithgowlights

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

I love the idea provided it has the following:

DMX in and Out - the reason is I want to add this to existing "gaps" in the display, OR I want to run a string of them off one output (i.e a number of leaping arches)

Seperate power in - For me this is a must. I will eithor be adding this into gaps in existing universes, or running a single string of 6 of these (150 pixels/450 channels) in one run. I want the option of injecting 24V DC into every node to avoid issues with power over DMX. Thus a jumper or wire link should be provided IF possible, or at least an easily cuttable track and "test points" we can use to inject power

Price. Yes we always get to this lol. This depends on if it is pre-built or a board for us to build ourselves. Build ourselves is always nice, but in this instance I dont care. $20 eithor way would be ideal, but we could always go a bit higher of course.

If these are included then I'd be interested in 6 or 8 as I want to do leaping arches and these seem like a good way to do them in Pixels. 100 to 150mm spacing, 25 pixels per group gives a good leaping arch.
 

Brownie

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P-DMX 25 pixel (2801 / 6803) controller with DC converter

I would agree with Dave (lithgowlights) and would be looking at doing something similar with them for leaping arches. I would be interested in 4.

Brownie
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

What do you guys think about the addressing + options part of it? DIP switches or a button?
 

neilric99

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

i like dip switches, unless the button as some indication of the mode that its in
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

I've done a partial layout (2" x 2") that incorporates a 10 way DIP switch.

That's 9 switches for the DMX address and one to select 2801 / 6803 mode.

Still thinking about the options though.
 

lithgowlights

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

Personally, I dont really mind, but dip switches do allow pc-less addressing, and slightly easier code
 

Wombat

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

ability to drive 42 pixels would be good. then I could use it for MPH pixels. I guess this is the limitation of the PSU you are building on the board. It is more expensive/harder to build a 3A PSU onboard

but 50 pixels per board would be nice then you can use 3 strings per universe.

If LithgoLights idea is incorporated with DMX in/out at least I could cut the strings in half to inject power in but makes wiring harder.

Would it work with 12V? then inexpensive Computer PSU's can be used.
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

There will be another board for > 25 pixels. :)

I'm just aiming for a simple controller with a 25 pixel limit for this one.
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

Just to clarify, the input voltage doesn't have to be 24V. It can be in the range of 10V - 30V DC.

However with higher input voltages, the voltage drop on the DC input cable would be less. (due to the lower current)
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

I completed the PCB design for this project last night. Here's what I came up with:

  • Compact size 50.8mm x 50.8mm (2" x 2")
  • 3mm mounting hole in each corner
  • P-DMX in/loop via 2x RJ45 sockets
  • 2 way terminal block for alternative DC input
  • Jumper to disconnect P-DMX power
  • Current overload protection
  • Jumper for DMX termination
  • Socketed MAX485 chip
  • On-board 5V 1.5A regulator to power 25 pixels
  • 4 way plug-in pixel connector
  • DIP switch for address & 2801/6803 mode select
  • Status LED
  • All through hole parts except for the PIC chip

I hope to get some prototype boards made in a couple of weeks time.
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

DIP switches 1-9 are for setting the DMX address.
DIP switch 10 selects 2801 / 6803 output.
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

I was thinking of a simple P-DMX servo board last night and realised that this 25 pixel board already has 95% of the parts required to do servo function.

So, I've shuffled some parts around and added 3 pin headers for 5x servo outputs. The updated board is still only 51mm (2") square.

The current available is still only 1.5A @ 5V, so may only suit lower current servos. It all depends on how much simultaneous movement is required.

In theory, I could write firmware to drive the servo output and the pixel output at the same time, but given the power limitation, I'll probably offer them with either pixel or servo firmware.

I also added a 2 pin connector for a possible trigger function later on. There was a spare 10mm space so I used it!

I plan to get a few sample boards made when we do out next prototype PCB run. Maybe in the next couple of weeks.
 

David_AVD

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Re: P-DMX 25 pixel (2801 / 6803) controller with DC converter

Here's the revised PCB design:

 
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