Analog voltage control by RS485

[duglus]

Hi everyone,

I have done my 485 communication in both ASCII & RTU mode. So, I have no problem to read/write any data through modbus(i.e. char, short, long & float).
But now I want to operate analog voltage i.e 0 to 10 V DC through RS485 communication.
So please suggest me details of any idea or circuitry.

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[dick_freebird]

Seems like you want a serial DAC; I bet there are some,
and you might like a "2 wire" interface (clockless / clock
recovery from the data stream). The DAC would probably
have a buffer amp for voltage & current-drive.

 

[antedeluvian]

I use the Adam modules by Advantech. They have their own RS485 protocol and some of them also work on Modbus.

https://www.advantech.com/products/Analog-I-O-Modules/sub_GF-5VTD.aspx

In particular I have used the ADAM-4024 4 channel D/A with Modbus.

If you want more options just google "Modbus D/A"

For what it is worth, I wrote a series of 2 articles entitled "Generic Modbus Simulator" that appeared in issues 200 and 201 (March/April 2007) of Circuit Cellar. In it, the simulator communicated with several ADAM modules.
**broken link removed**
**broken link removed**

If you are interested in creating your own D/A, you may be interested in a follow up article "Create A Modbus Slave" that appeared in issue 216 (July 2008) of Circuit Cellar.

**broken link removed**

-Aubrey

P.S. Circuit Cellar's business model is to charge a nominal amount to download the articles.

 

[karesz]

Hi duglus,
I think its a job of 2x SO8 chips; a small PIC + a Serial DAC with voltage output...
K.,