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Thread: Long Distance Communication over RS485 with Teensy 4.0

  1. #1
    Junior Member
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    Sep 2020
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    Long Distance Communication over RS485 with Teensy 4.0

    I'm hoping to run a slave/master system over a distance of about 200 feet using an RS485 cable and a Teensy 4.0 on either end. I'm very new to this and have a few questions. I need to pass a few different signals from point A (i.e. joystick, a switch, etc.) to control a device in room B. Is there a specific breakout board that I should use to interface between the Teensy and the cable (I've seen several for use with Arduino Uno, but I can't find any information as to whether they are compatible with the Teensy)? I was also looking to use the Arduino Modbus library for communication but I'm also not sure if it works as is or if changes will need to be made to it? Or is there another library that would work better? Any suggestions would be helpful!

  2. #2
    Senior Member
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    Feb 2018
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    Corvallis, OR
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    Rather than RS-485, you might consider a pair of 915MHz transceivers. They should handle 200 feet unless one or both ends of the link are RF-shielded. You can probably find a pair of transceivers on Amazon for about $35. I have a set which has one unit with serial I/O and another that plugs into a USB port on my PC. You would need a pair with serial at both ends.

    One downside of the telemetry radios might be transmit and receive latency as the serial I/O goes through the packetization and transmission process.

  3. #3
    First dig up a copy of "The Art and Science of RS-485" which appeared in Circuit Cellar Magazine some time ago. A pdf usually turns up in a Google search. 200 feet is fairly short for RS-485 although it does vary with bit rate.

    The only tricky part is keeping the transmitter on until the UART finishes sending data. As for interface ICs, I prefer the MAXIM parts. There are many to choose from such as the MAX3430.

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