Raspberry Pi and Wireless RS485 Data Acquisition

We have just completed testing our re-designed wireless hat for the Raspberry Pi 3 and our Zigbee to RS485 converter for the 900 MHz S3B series from Digi.

This system worked right out of the box with simple programming using the Digi XCTU program.

The RPi 3 was configured for Modbus RTU protocol and using the new RPI3 wireless hat by VP Process Inc.

The analog 8 channel 4-20 mA input module is connected to the RS485 to wireless converter, which is also available in a DIN rail enclosure.

The typical application for this would be where the data acquisition (or control) are located some distance from the controller, in this case the Raspberry Pi. Using the 900 MHz modules proved to be very easy to use, and the distance (indoor range about 2000 square feet) had no effect - everything just worked!

Some things to be aware of for the application programming:

  • We used a "Packetization Timeout" value of 10 in the XCTU program
  • Use "Transparent mode" in the XCTU program
  • In the RS485 Modbus RTU protocol part of the app program, allow enough "Receive" timeout to allow the S3B (S2B,S2C) modules to communicate

Think in terms of $$ per foot for conduit in an industrial application versus the cost of some simple interfaces and a couple of radio modules. Depending on the distance of the "wire replacement", the savings can be quite significant!

More information on these modules can be found here:

RPi3 Wireless Hat

RS485 to Wireless Converter





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