A DMX512-interface for RS-232?

[apolloe]

Hi,

I'm seeking to build a simplest and cheapest possible DMX512-interface for my PC. I have no access to microcontroller programming tools, so I woud prefer a desing that uses no microcontrollers.

Would it be possible to generate the needed signal directly from a RS-232 -port? I am aware of the fact that the nominal maximum data rate for RS-232 is around 120000 bauds and the DMX512 needs 250000 bauds, but I have heard that some modern PC computers a capable of outputting 250000 bauds from their RS-232 ports. If this the case, could I simply use a RS-232 to RS-485 -converter, sold by, for example, Black Box?

Thanks in advance,

Juhana Saarinen
Helsinki, Finland

[Tomi Engdahl]

I'm seeking to build a simplest and cheapest possible DMX512-interface for my PC. I have no access to microcontroller programming tools, so I woud prefer a desing that uses no microcontrollers.

The DMX dongle described at http://users.skynet.be/kristofnys/
would be propably the simplest and cheapest widely supported (supported by many software, both in Windows and Linux systems) PC to DMX-512 hardware. I have not yet built it, but I plan to build it soon.

This design is based on PIC16F84 microcontroller. This microcontroller can be programmed pretty easily with very simple hardware (can be easily built form parts that cost just few dollars/euros) and suitable programming software. For example software and hardware at http://www.epanorama.net/counter.php?ur ... index1.htm can do the programming well. That's what I have used. The program documentation page describes the supported programming hardware. I have used the JDM / Lupido circuit, which is quite simple as you can see form the circuit diagram:

Would it be possible to generate the needed signal directly from a RS-232 -port? I am aware of the fact that the nominal maximum data rate for RS-232 is around 120000 bauds and the DMX512 needs 250000 bauds, but I have heard that some modern PC computers a capable of outputting 250000 bauds from their RS-232 ports. If this the case, could I simply use a RS-232 to RS-485 -converter, sold by, for example, Black Box?

If you have RS-232 hardware that is capable of outputting data at 250 kbit/s speed, a RS-232 to RS-485 converter capable of operating at that rate and suitable software to drive that card, then there should not be any problem in creating DMX-512 signal in this way. None of the normal RS-232 ports I know can support this rate normally (I know some that support several multiples of 115200 bps, like around 230 kbit/s). Maybe such high speed card not naturally supporting 250 kbit/s could run at that rate by changing the clock crystal for the UART IC (I once thought trying this method, but never got this this project ready)...

Many commercial RS-232 to RS-485 -converters I know are designed for slower data rates than 250 kbit/s.... you need to find one that is fast enough.

I rember seeing one USB-to-DMX512 plan that was based on USB-RS232 converter design, just the line buffer IC after UART was changed to RS-485 trascevier (for example MAX232) (instead of normal MAX232 type buffer foudn on stanard adapters). The USB interfacing IC was set to run on 250kbit/s speed on serial side, and supplied with suitable drivers that made it compatible with DMX-512 software...

[Tomi Engdahl]

Here is some update to my eariler article.

I just built the the DMX dongle described at http://users.skynet.be/kristofnys/

As you can see from the circuit diagram it is quite simple:


It seems to work well with DMXControl software on the first tests.

More useful DMX-512 information can be found at http://www.epanorama.net/links/lights.html#dmx512

[ben.suffolk]

A little late in the day for the original post, but it may be of use to somebody else. I have designed and built a bus powered USB interface thats fully opto isolated and allows simultaneous input and output of a full 512 channel universe. Its microprocessor controlled to ensure accurate (and fast) DMX timings, and you only need to send / receive changed data to the host application, so its quite efficient for the host computer.

Comes in around £66 quid to build, depending on where you buy the components from.

Details can be found at dmx512.vanilla.net

Hope this is of some interest

Regards

Ben