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RS485 question

Discussion in 'Electronic Design' started by joble, Aug 29, 2003.

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  1. joble

    joble Guest

    Hello,

    I'm building a DMX-sender and receiver for distances up to 150 meters.
    DMX works with RS485 and this is able to do this, so no problem.

    I have a few questions:

    1) I want to use the SN75176 as an RS485 convertor. Are there better
    options?

    2) How should the topology of the transmitter look like? I think this
    can be made the most easy way. DMX-shield to ground, and DMX- and DMX+
    directly to the outputs of the RS485 driver. I'm i right or are there
    better ways to do this.

    3) Same question about the receiver. I see many manufacturers connect
    DMX ground to the logical ground on their PCB, but i do not believe
    this is the right way to do it. The data pins might be connected
    directly to the 75176 with a 220K resistor from the DMX+ to +5V and
    from the DMX- to ground. Again, is this ok??? Has anyone examples of
    an isolated receiver schematic?


    Thanks!
     
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