Looking for DMX512 schematics

[RussMartin]

I am looking for some generic DMX512 encoding and decoding circuits. Any suggestions?

[Darrel Taylor]

Look for RS485 instead, to get a circuit.

The decoding is done in software. (well for a PIC it is).
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[ShoKre]

i think not so eassy, (250kb11bit/specialstart-stop timing)....

give as some links if this is so easy....

I'm verry interested...

... googling you can find only asm stuf, with wery reserved explanation..
i think transmit is posible with asm-software sending routine combined with basic logic....

but for reciving, if someone know technics for capture (firstline bracket)
this shud be interesting post...

[RussMartin]

Thanks, Darrel!

I can handle RS485 with a Maxim product. I should have put the question differently.

Can someone point me to some generic software?

[DynamoBen]

If you do a search of this forum you will find some snips of code. Beyond that there is ASM code if you google. Keep in mind that there is more than one way to successfully decode DMX. Each method has its pros and cons. Make sure you have an in-depth understanding of the protocol before you begin.

[RussMartin]

Thanks, ShoKre. I already have an ENTTEC open USB interface for the transmit side, so I'm looking for ways to do the receiving.

[DynamoBen]

The forum has a few examples; one posted by me. I too am using the OpenDMX device for transmitting. Keep in mind that a "real" DMX transmitter transmits much quicker than the OpenDMX device (44Hz). I found that my code worked well when attached to the OpenDMX but didn’t work reliably on a standard lighting console. Have fun!

[RussMartin]

Holy smoke!

I assume you mean that your receiver didn't work on a standard console? How reliable/unreliable was it--total fiasco or just partial?

My ENTTEC (running under LightFactory, not the freeware stuff) runs the few DMX512 devices I've tried.

How did you arrive at the 44Hz (!) figure? Scope, specs, what? If it's truly that bad, I'm going to send the package back.

Can you give me a link to your code and/or schematic?

Thanks!

[DynamoBen]

I assume you mean that your receiver didn't work on a standard console? How reliable/unreliable was it--total fiasco or just partial?

My ENTTEC (running under LightFactory, not the freeware stuff) runs the few DMX512 devices I've tried.

My receiver worked fine at the slower speed of the ENTTEC (25-30Hz) but didn't run so well at full speed on a console (44Hz). I am trying to narrow down the bottle neck. The ENTTEC device runs DMX devices just fine, it’s an inexpensive way to produce DMX on a PC which is why I'm using it. That being said I still do final testing on a commercial lighting console.

How did you arrive at the 44Hz (!) figure? Scope, specs, what?

The DMX spec is where I get this number. With all the testing I've done the fastest the ENTTEC can transmit reliably is about 33Hz. Beyond that you start to see periodic errors. Visually you would never notice these errors I used a DMX tester to determine the highest refresh rate the ENTTEC could handle.

If it's truly that bad, I'm going to send the package back.

Not sure what you mean here.

Can you give me a link to your code and/or schematic?

The best resource is the search at the top of the page. There are a number of posts on this topic. In the search field type DMX* and you will get several hits. Beyond that learn and understand the protocol. Once you do all that it’s fairly easy to create the code.

[RussMartin]

Since posting my reply, I had the opportunity to talk with the US sales rep.

Apparently, with the OpenDMX, the computer is having to do all the timing chores in software. How close the result is to the "standard" 44 frames per second depends on how much other stuff the computer is trying to do at the same time. When too many demands are made on the computer, he said it starts "dropping" packets.

He also suggested that the USB DMX Pro is a way to eliminate the problem, for $95 US over the cost of the OpenDMX.

http://www.enttec.com/index.php?main...name=dmxusbpro

Thanks for helping me out with this!

[bcd]

Russ,

44 times a second is not a bad refresh rate. The DMX spec allows upto a 1Hz refresh rate, although the fades look a bit 'jumpy'. I own a Martin Lightjockey system and it has the options for 44Hz, 22Hz and 11Hz transmission.

44Hz is fine for most moving rigs. Personally I have code that will transmit DMX from a PIC at 80Hz, but that runs a tight loop with only 24 channel frame, but have found that a quick refresh can sometimes freak out some of the cheaper Chinese style scanners.

The Enttec stuff is great, but I would recommend the USBPro interface as it is also isolated and has some more funky software options.

From the Enttec site on the USB Pro: http://enttec.com/index.php?main_men...name=dmxusbpro
<snip>
# Refresh Rate configurable from 1 to 40Hz with a full 512 channel frame
# Break configurable from 96uS to 1.3mS
# MaB configurable from 10.6uS to 1.3mS
</snip>

Bill.

[grich]

sorry my mistake