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Potentiometer That Does Modbus RTU Via RS232 or RS485
I need a knob that can control a timer in my plc but I have no analog inputs.
By Newbie in need. on 23 May, 2017 - 12:44 pm
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I am working with a click plc (C0-01DR-D) from automation direct. I need to interface with an internal timer but my model does not have any analog inputs. To get an analog input and keep the number of relay outputs I need is going to cost me another $90, so I am looking for a way to use a knob control without one. The tech from automation direct tells me the only way is to find a potentiometer (knob) that does Modbus RTU via RS232 or RS485. So far I have been unsuccessful in my search. if anyone knows of one I can buy, or a way to use a normal potentiometer with the tx/rx port, it would be greatly appreciated.

By Ikhtiander on 23 May, 2017 - 8:43 pm

Hello Newbie in need,

Quick idea from me, you can use Arduino connected to AD5171 Digital potentiometer and also embed Modbus code into the Arduino
so you will have your click PLC talking to electronic potentiometer :

https://www.arduino.cc/en/Tutorial/DigitalPotentiometer
https://playground.arduino.cc/Code/ModbusMaster

hope this help

Thought about using two discrete inputs? Raise/lower a counter that is the timer set-point.

Set a limit to the ramp equivalent to the longest/shortest time you require.

I assume you can display a number

Optional
Start the count up/down by 1 then accelerate with time like a typical digital device set-point.

By Steve Myres on 24 May, 2017 - 5:25 pm

I'm pretty sure that if a pot with Modbus interface exists, it costs at least $90. I've actually never heard of such a thing. Though you could certainly make one out of Modbus remote I/O and a pot, but that doesn't gain you anything over replacing the Click. I thought they had analog expansion modules anyway?

I assume you have a way to display the timer settings?

You could simply use DI's and pushbuttons to increase and decrease the timer settings. Also to start, stop and reset.

You could also use a simple text based HMI with pushbuttons. It should be inexpensive.

good luck