Serial to 4-20mA output

J

Thread Starter

John Brohan

C

Curt Wuollet

Hi John

I have seen serial D/A's that could be used to make such a beast with some analog electronics behind to offset and scale the output to 4-20ma. I doubt you will find something like this as serial is not a very precise term. The D/A's would have their particular protocol, bit/byte order etc. If you can provide this format it's
doable. If you want one to run with _your_ protocol it will almost have to have some sort of processor for conversion. Try Maxim for silicon. Another alternative would be a small SBC with serial and D/A ports.

Regards

cww


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A

Andrew Kohlsmith

> I have seen serial D/A's that could be used to make such a beast
> with some analog electronics behind to offset and scale the output
> to 4-20ma. I doubt you will find something like this as serial

There's no need to use a DAC unless you really need it... I've generated pseudo-PWM with a serial port. It's very easy and the stability really isn't too bad either.

If you just set up the serial port and start spitting out a bitstream and filter the output you'll get a variable voltage out. Unfortunately the RS232 spec doesn't require absolute voltages to be output so your actual filtered voltage will vary from PC to PC. However if you use a few
transistors you should be able to get a nice 4-20mA output without too much fuss.

0x00 won't give you 0V since you still have start and stop bits but it will be quite low. If you just play around with it you may be surprised. Hell I may start playing with it and get a little circuit for the project. :)

Regards,
Andrew


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R

Robert Schwebel

You'll find such a module (for RS485, converters to RS232 are available) in the ICPDAS I-7000 series:

http://www.icpdas.com.tw/products/7000/i-7021.htm

They have distributors all over the world.

Robert
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