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Emulate RS422 touchpad with microcontroller

Discussion in 'Microcontrollers, Programming and IoT' started by ProfessorC, Apr 3, 2017.

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  1. ProfessorC


    Apr 3, 2017
    I have an old multi-zone amplifier that used to be controlled via up to eight LCD touchpads throughout the house.
    These touchpads were connected to the amplifier by CAT5 with RJ45s at each end. I assume it's based on RS422.

    I would now like to use Arduino(s) or Rasp Pi(s) - instead of the touchpads - so I can use IFTT or other and control the amp via mobile device and/or web browser.

    How can I
    • reverse-engineer the communication protocol so I can emulate it
    • connect the microcontroller to the RJ45 ports on the amp, and send the emulated commands

    I'm also trying to work out if I would need a MC in place of each of the eight touchpads, or would there be a way to stack shields so a single MC could control 2 or more (or all) of the zones?

    Any help or pointers would be awesome.

    Thanks in advance!
  2. ArmRules


    Feb 8, 2012
    If all keypads are connected to the amplifier by individual cables it may not be a multidrop bus like RS422 or RS485. To confirm you need to to check if the touchpads are daisy chained or star connected. The use of an RJ45 connection may only be for convienience for a properitary point to point connection, or alternatively unsused cores in the cat 6 could be used to accomplish the daisy chaining. Is there any switch or connector marked "terminator" on the keypads or amplifier or any address selection switch? (This indiates an adressable bus)
    Once you establish what the connection scheme is you can progress to the next stage as this will dictate what you need to do to solve your problem.
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