Sending RS485 signals to a device from an Arduino

Projects Networking, Protocols, and Devices
1

Hello Everyone,

I am wondering if it is possible to send RS485 signals to a device from my arduino. I have this stepper motor driver/controller (http://www.linengineering.com/LinE/contents/stepmotors/R256.aspx) which communicates via USB through a USB / RS485 converter sold by the same company http://www.linengineering.com/LinE/contents/stepmotors/USB485.aspx.

The driver/controller takes relatively simple serial commands and spins the motor. I bought a USB / RS485 converter from SparfkFun (SparkFun USB to RS-485 Converter - BOB-09822 - SparkFun Electronics), although I am pretty sure this device will not work with the usb port on the arduino. I have been reading other posts about this communication protocol although its just not clicking.

Am I on the right track?

2

You cannot communicate directly as the RS485 has different voltage levels (-7/+12V). As with the RS232 where you use a MAX232 there is a MAX485 which does that conversion for you.

3

It appears that that gadget talks 485 out the DB9 connector so USB has nothing to do with it if you want to control it from an Arduino.

You need to add an RS-485 transceiver (MAX485, LTC1785 etc etc) to the Arduino and connect it's A and B pins to pins 4 and 3 on that DB9, also connect GND. Then run the transceiver's Tx/DO pin to the Arduino, probably on a digital IO pin and use Software Serial.

As I assume the comms is one way tie RE and TE together to GND.

Rob