Forum

RS232 Baud Rate


#1

I have a USB to RS232 adapter that creates a virtual RS232 port.
It supports anything between 300 and 1000000 baud.
in vvvv I can only choose most common bauds. I want to specify the rate myself (as there is no standard in what is allowed)

I want 250000 as it happen to be the rate for DMX. No idea though if it will work but I still want to test. The receiver it a Light board to it don’t have to drive cables or fixtures.

Any ideas?

edit hmm. is seems there is no start bit available so it might not work properly.

Maybe it could be made up of 4 bit long pulses at 1M baud. But then I would need no stop bits or else they would be in the way.


#2

obviously there is a significant electrical difference between RS485 and RS232, so you would need some electronics anyway.

changing the RS232 (Devices) node to accept other baud rates sounds like an interesting idea, which might be implemented at the same time, when we also rework it to make it faster or spreadable or get the stupid connected pin working, which always just reflects the enabled status and doesnt check the connection status of the port.


#3

Thanks.
Do you think a simple 555 (or a few) would do the trick.
Or a simple OP amp with one line inverted to you simply change between polarity for the output when the RS232 calls for high. I don’t have a lot of EE background when it comes to this so I could have understood the signaling scheme wrong.

Any way to add the start bit?
Or omit the stop bit and do some math to add them in by binary.

It would be nice to make a simple and cheap DMX output. Most found online is too expensive.

I wonder if programming an AVR would do. But they are not cheap ether.


#4

using something like an opamp or a couple of transistors will surely do the trick. just make sure to have a oscilloscope to know what you are doing.

on the other side there are many little circuits on the web (like http://dworkin-dmx.de or http://www.ulrichradig.de/home/index.php/avr/rs232-dmx - unfortunately both in german) which do little computer based rs232->dmx converters which look not really more complex (probably they involve many thousand times more transistors, but from the component count it looks quite comparable). this frees you from any baud rate issues.

another strategy would be writing a little c# plugin which configures your usb com port in the correct way. see HowTo VVVVPlugins and system.io.ports.serialport at MSDN.


#5

After further reading it seems there really is a start bit that matches. So RS232 really is compatible with DMX from a logical standpoint?
Just electrical differences.
How about a RS232 to RS485 adapter?
Like this
http://www.hexin-tech.com.cn/pages/index.php?mainframe=cHJvZHVjdF9kZXRhaWw=&product_id=MTk5&big_catalog=
Or more specifically this http://www.dealextreme.com/details.dx/sku.6040
But I think they are the same.
As far as I can see it’s passive to I’m not sure if the baud rate would be a problem with short cables.

The controllers you posted seems nice and simple. Ill have to look into that as well. Thanks.

The USB to RS232 converter I have is basically this http://www.ftdichip.com/Products/FT232R.htm
The chip is FR232RL


#6

these adapters are so amazingly cheap - there must be some really really simple electronics inside. note that they are speced only for max 115200 BPS, but if you make the rs232 cable very short (basically just connecting the FTDI to the adapter this could work. even with 10m cables i had never any issues with the higher RS232 rates, so 250000 BPS might work perfectly.

google gives a lot of ideas here. the note written on top of [http://www.airborn.com.au/layout/232to485.html](google](http://images.google.de/images?num=100&q=RS232%20to%20RS485%20schematics) gives a lot of ideas here. the note written on top of [http://www.airborn.com.au/layout/232to485.html) scares me a little bit, at is indicates that these adapters might require some nonstandard handling of RS232 handshake lines.

anyway, its a nice perspective to have DMX out (and DMX IN) for 6$ - so give it a try.