GSM+RS485 with Arduino UNO


I'm trying out on a requirement on Communicating a VFD with RS485 protocol with Arduino UNO and sending the data using a GSM Module. Is it possible to do RS485 communication and GSM Module communication using a single Tx and Rx pins of Arduino UNO??

I'm also struck facing the same challenge and thus seeking your support.

Can you please share more details on this to

Awaiting for your response.

Shree Harsha K

Describe the chain of equipment You think about. From where/what will the communication start? Make a block diagram.

I intend to read the data from VFD using Modbus and then send the data using GSM module.. Can we record the data simultaneously in Spread sheet / Google sheet say every 4 hours ??

Also can anyone suggest what should be the Type of GSM module for attaining this functionality ??

Thanks! Exactly what I had in mind.
That should be doable. On thing to check up! Check the rate of data sent. Receiving, storing for a short time and transmitting, takes some time, depending on the size of the data packages.

You need to know what type of GSM is available in Your place. Then You can look for a proper GSM module.

Hi . Thanks for the input .

Can you please suggest how i can Use Uno to simultaneously use serial communication as it has only 1Tx and Rx Pins. I need to Use Tx,Rx pins to communicate with VFD using RS485 communication and also use the same Tx,Rx to send data to GSM Module .

By the way , i'm in INDIA so i'm planning to use SIM900A GSM Module.


When You create code it's very useful to use the USB connection for downloading, and debugging. The Tx, Rx, (digital 0 and 1) are use by the USB interface on the board.

I think that SoftWareSerial can be used. That works from digital I/O pins.
Can You post links to the 2 devices, or check Yourself?

What i Understand is i can use Pin 0(Rx) and Pin 1(Tx) to Receive data from VFD using Modbus Communication and Then Configure Pin 2 and Pin 3 to send the received data from VFD to GSM Module ??

Please correct me if in case i have understood it correctly.

Yes, You are right, but.....
Pin 0 and 1 are very good to use for debugging, in Serial monitor and serial.print, during the time You develop the code.. Therefore I strongly recommend that You do not use those pins in the project.
I am not sure if there is any limitation for SoftWareSerial, what pins, running 2 SWS at the same time.
One solution can be to use an Arduino Mega. The Mega has 3 hardware serial ports.
Do some research about any limitations for SWS.

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