New DMX dongle

[RJ]

Ok a few assuptions I'm making for this to be a benifit:

Some users already have the cheap usb to serial convertors that can handle the 115K speed (most all can do this its the faster ones that cost)

For those that dont these cheap units cost very little $9 - $20

for some of our members the current offerings of DMX dongles at $60 - $150 is a healty expense.

That the majority of the members are not running lights shows of over 192 channels.

Ok, if this is true then here are some facts :

It is easy to write pic code to send dmx data.
Pic's are cheap
It is easy to write code to recieve 115K serial data
streaming serial data out to the usb to serial convertors is easy for vixen

With this in mind what about this for a cheap homebuilt DMX solution of our own.

Program a pic to recieve a 115k stream of data from vixen just like you do for the entec pro dongles and then to send out the dmx stream from the pic.

So you would have a little sub dongle that plugs into you serial convertor and then you plug you output cable to it and you have DMX. The pic would keep up the dmx stream not the computer just like in the Entec Pro.

The first thought is 115k is not fast enough from the port to feed a dmx stream. This is true for a full 512 channel stream but what about a trunucated or "Short frame" of 192 channels. hopefully you agreed that most of use do not even do 192 ch shows. The data stream would be legitimate dmx and should work other dmx equipment.

The end would be a product for those not wanting to speed the money of the more expensive solutions and not needing 512 channels on one usb port.

I believe this would be a very inexpensive way to do this.

Let me say right up front I am not purposing this for myself I will gain nothing from it I am simply trying to come up with a dirt cheap alternative for our members to use that would like to move to dmx. I am in hope that in time the equipment the DIY'ers are using can move to one protocol which multiple different devices can use instead of continuing to create devices that all use different protocols which require each different type of device to be hooked to a different port and another feed from our computers. I know the value my opinon carrys here but I would hope good ideas are universial. I have learned from the other indurstries I work and play in that without a common standard to work from progress slows. If the computer industry had not given up all the different companies independant standards and settled on solid standards across the industry you would not be reading this right now. (so you can blame them).

[KC]

If I understand correctly...

Your PIC-based dongle would be maintaining the DMX stream, as you stated. The data from the PC would only be used to update the state of the channels in the DMX stream periodically.

Doing the math...@115,200 you get 14,400 bytes/sec...to update 512 channels at 25 ms (because that number has been thrown around) with 1 byte/channel = 20,480 bytes. So even at 115k, you could still get the full 512 channels of a single universe by taking your timing down to roughly 40 ms (or greater). This doesn't account for any overhead in the packet structure, but still, at 50 ms you could easily fit the full 512 channels. At 25 ms, you're limited to around 360 channels (no overhead accounted for), which is still pretty decent.

This, assuming that I'm on the same page as you...? It sounds like a less expensive version of the Pro unit.

[RJ]

KC,

You are dead on with my thinking. I was using conservative numbers to make sure we can hit what we are saying. Would rather promise 256 channels and be able to deliver 360 than the other way around. And we all no theres overhead that we take a bite out of the perfect world numbers.

[DynamoBen]

I've had a similar thought for a while. My "dream" would be to have a common serial protocol (Vixen Serial Protocol = VSP). This protocol would allow anyone to create any kind of conversion dongle they want. So it could be VSP to DMX, or VSP to Renard. All vixen would do is send out intensity up dates. That gets everything onto one common plug-in.

As far as refresh and configurability that would be left up to the dongle. So the developer could make a little programming app that could change things like number of channels transmitted and what not.

I think its a worth while project, but the first thing is to come up with a protocol. Since I've been toying with this idea for some time I have a skeleton of a protocol. Thoughts?

[andyhough]

I work for an integration software company. We have integration software that allows our 130 or so application adapters to plug into a bus similar to the PCI bus on a PC but for software. There are several protocols already available, like Web Services over TCP or Java Mesage Services. Many of them are shareware.

My thought is that finding a standard that already exists, and building an the VSP adapter to plug right into it, would offload a lot of development, and allow any number of adapters to be added later. If you would like to chat more, this would be a nice project for me to get my teeth into for next years, "nifty use of our technology award"

[DynamoBen]

I'm with you in spirit. I'm of the mindset that if I we were to follow any standard it should be one adopted by the lighting industry. I guess the issue is that there isn't really anything in the lighting industry in the way of a standard serial protocol (except for maybe midi). That being said recently the Ethernet standard was finished (ACN) which should help some with future Ethernet based devices.

As far as serial I feel like it should be pretty simple to implement, expandable, and as usual free. The skeleton protocol was as simple as a header, data type identifier, data, and footer. Initially controllers and dongles will use the protocol but over time it will be used to remote control vixen, hence it needing to be expandable.

I would love to see what you come up with, as you find info post for the group and we can discuss it. It’s always hard to standardize but I think it’s worth trying to do.

[RJ]

I think it's time we raised this idea from the dead!

I dropped it as there was very little interest in DMX at the time but it has gained some support so I worked out a couple of design for this. It looks like on the DMX Pro Dongle The fastest that the port settings in Vixen will go is 115K so unless it does not matter and vixen can run faster than that on the usb even with it set that way in the plugin ( help us out on this KC) I have tested 512 channels at 25ms on my setup and it seems to update find. I only had 216 channels in use but I tested it all with vixen setup with 512 channels and had the extra channels doing random stuff. with that said the usb chip is the only problem it is surface mount so we would Have problems with most users building it this way. I could solder it and some other here could but we have to plan for the majority. (It's a .8mm pin spacing so its not super small as they go.) So we could either go with a all in one design and I have asked JEC if I did this would he help get me setup with the people who build his stuff to have them built for us. ( parts would run about $15 minus pcb and assembly.) this would allow full usb speed if vixen can do it, to update the DMX stream. Or we could revert back to my first Idea on this thread and use a cheap usb to serial port adapter and then I use the other design which would be basicly a big pic with enough ram for a full DMX universe and room for working space and a Euart to communicate with the serial port. It would create and stream the DMX stream. Both methods would function like a DMX Pro where the pic does the stream to maintain good timming and the computer and vixen just spits out changes. I have my dongle so I'm set but I am simply trying to help out the community. I believe there is no reason I can not do this. I have enough time playing with DMX firmware that I have become very comfortable with it and I know the pics I work with can communicate easily at 115k. as far as serial protocol I would stay with the DMX pro's protcol so it works with the current plugin.

If we do this I see no negative to DMX for our users and so I am willing to do the work if others will fund the proto's just like with the Freestyle. It would be about $14 a piece for the proto boards for 4 people. I will buy the parts for my proto work.

Lets get a dialog going on this let me hear your thoughts on it.

I would start right after we order the proto boards for the Freestyle if that works out, if not as soon as I come to the conclusion the freestyle isn't going to pan out.

[DynamoBen]

Something important to keep in mind. Even though the baud rate is set to 115K the USB interface actually runs at close to 3M. The Pro uses the FTDI USB to Parallel interface. In the documentation it states that a baud rate must be set but the interface will communicate at a much higher speed in this case up to 3M.

While my math isn't great I do believe that you will run into a bottle neck if all 512 values are changed simultaneously at 115K. So if you go the serial route you may need to be a bit "crafty" in your approach.

I'm all for it if you can get it to work.

[rrowan]

Hi RJ

I really love this idea. I read this post when I first join up here and was hoping it would come back from the dead.

While I am just starting out and will be using a Grinch board for 2008. I can see going to DMX after that. The cost of the Pro box was a major factor and then there is a cable conversion from the 5 pin (bnc?) to I guess rj-45.

So yes I would like to help get this going.

Thanks

Rick R.

[snething]

Great work RJ! Count me in to help fund or test this project!

Thanks