DMX DC board I'm thinking about building

[timon]

After seeing the MY994X series of chips that MrPackHead, thank you for the inspiration, was working on and since I need something like them for my display I decided to look into building an 8 channel 12-48VDC DMX LED PWM dimmer based on the chip set. Let me be up front and say I don't know yet if I will build it and if I do I don't know if I'll make it available. There was so much unrest about the 44 project that I really don't want to end up in a mess as well. We'll take this slowly first seeing if I built some prototypes and then decide where we go from there.

One of the reasons I looked into building these is because I'm trying to keep any 120VAC out of the display area where anyone can get to it so all of my props will be DC powered and all the power supplies will be located in a safe area and well grounded. To do this I needed something less expensive controller than the LOR CMB16D-QC to run my HolidayCoro singing Pumpkin, Monsters and Trees or any other non pixel props I build. So to that end I rebuild cheep LED AC half wave strings so they run on DC. My singing props will run from 48V power supplies which allow me to use 14 3.4V LEDs in series and even more of the 2V LEDs. As an example my HolidayCoro Pumpkin takes less than 1/2A at 48V. One nice thing about using converted strings, these is only about 1/3 of the wire on the back side of the Pumpkin compared to using AC strings.

Back to the board, it will accept power from either a direct connection or through P-DMX and I even tossed in an extra two jumpers incase one want to use pins 3 & 6 for additional power, aka, JR's standard for PixelNet. It does not support the HolidayCoro power standard as it's just too different from the others and I didn't want that many jumpers.

I designed the board with two mounting hole patters. One for the TA200 and the other for the CG-500 or CG1500. I didn't do the CG-1000 which uses the old hole pattern. When used in a CG-1500 there should be room for 3 boards and a power supply or 6 boards although I really can't see having 48 channels in in a single enclosure. The whole point of the TA200 is to get the controller at the prop with as few cables as possible.

One might be able to make this cheaper using a PIC chip but the MY994X series has gamma adjust which should allow for better LED dimming.

Here is a drawing of the proposed board installed in a TA200. I'll post more if I continue with this.

[P. Short]

I don't think that you can run 14 3.4V LEDs from 48V, since 14*3.4V = 47.6V. This doesn't leave enough headroom for whatever current control scheme that you're using and to account for the variability (tolerance) of the LEDs and the power supply. You'll get more consistent results with fewer than 14 LEDs in series.

[dmcole]

Timon:

Looks good ... I appreciate the fact it supports lower voltages even though your environment requires 48v.

On supporting the power standards, did you mean to type "aka, RJ's standard for PixelNet"?

I would think that there would be more call for the HolidayCoro P-DMX than PixelNet ... once you've converted the signal to PixelNet, you couldn't use it in a DMX environment anyway (or am I missing something?).

Good project; better man than me, Gunga Din.

\dmc

[timon]

I don't think that you can run 14 3.4V LEDs from 48V, since 14*3.4V = 47.6V. This doesn't leave enough headroom for whatever current control scheme that you're using and to account for the variability (tolerance) of the LEDs and the power supply. You'll get more consistent results with fewer than 14 LEDs in series.

Actually I did 15 LEDs on my pumpkin using my CMB16D-QC controller. Each string was running at about 16ma, which comes out to 3.2V and it's still very bright. The MOSFETs have an extremely low on resistance and the ones I'm using are even lower than the ones LOR uses. I could drop down to 13 and will look at this when I build the next props. I'll post a video of my pumpkin shortly.

BTW, Here is the latest board layout. It's getting close to deciding if I'm going to build it once I finish the parts list and see what the parts are going to cost. The biggest issue is sourcing the MY9942SS and MY9943SS in other than full 2,500 piece reels. This is not a board one wants to assemble more than a few by hand. Well at least I don't

John

DMX 8 Ch MOSFET TA200 Layout.jpg

[timon]

Timon:

Looks good ... I appreciate the fact it supports lower voltages even though your environment requires 48v.

On supporting the power standards, did you mean to type "aka, RJ's standard for PixelNet"?

I would think that there would be more call for the HolidayCoro P-DMX than PixelNet ... once you've converted the signal to PixelNet, you couldn't use it in a DMX environment anyway (or am I missing something?).

Good project; better man than me, Gunga Din.

\dmc

Yes, RJ's scheme only differs from P-DMX in that he adds pins 3 & 6 for additional power capacity.

David is a smart guy but I personally believe he made one mistake when he setup his wiring scheme which is that pins 7 & 8 are not both ground, one has power and the other is ground. If you plug a standard DMX board in that uses a RJ45 connector then you end up shorting out the power supply. If I'm mistaken on this would someone please let me know but that's what I though he did based on the videos I watched. By using the P-DMX layout you can use off the shelf power injectors that don't cost much. So, I'll take another look at what would be need to have a full jumper arrangement which could support Davids power scheme and see if there is room on the board to do all three.

My biggest problem right now is that I don't have a work station for SMD just through hole. I'm looking at what updating my station will cost verses having a local build house make me a couple of prototypes. It's a easy board for a rework person to make by hand when you have the right tools.

John

[P. Short]

How are you controlling the LED current?

[timon]

How are you controlling the LED current?

With the external MOSFETs the board will run in constant voltage mode so you have to control the current external to the board. This is not a problem when using any of the RGB modules but when your using it with long LED strings you'll need a series resistor to limit the current. Basically it's the same way that the LOR CMD16D-QC drives it's loads and the same as the ones that HolidayCoro sells other than this board has a breakdown limit of 60VDC rather than 12 or 24. I run 48V so I can have as many LEDs in series when making my singing faces or any other prop that needs a lot of LEDs.

OMT, for DMCOLE

It looks like I can get the jumpers on the board so I can do HolidayCoro's power scheme.

[Matt_Edwards]

How does JP1 work? I can't see how the voltage selection works.
Cheers Matt

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[timon]

How does JP1 work? I can't see how the voltage selection works.
Cheers Matt

Sent from my GT-I9100 using Tapatalk 2

The MY994X chips have their own regulator but he chips can only handle a maximum of 40V. As long as the input voltage is below 36V I don't use regulator. If I'm going to run above 36V the regulator is used and powers the chips with 30V.

I'm using the LM317 regulator and I expect that because of the way it's designed you could leave it in circuit and it would supply the ICs with input voltage less the output transistor's vSat until the input voltage goes above it's regulator set point however I'm not comfortable running it that way.

[Matt_Edwards]

Sweet.
Re: smd don't be scared of having a go with the tools you have.
Screens,hot air irons, solder paste dispensers make it easier,but are not a must.

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