opto-isolated serial interface cable

Discussion in 'General Electronics Chat' started by Mad Professor, Mar 28, 2011.

  1. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    Good day to you.

    I am looking for help and advice with regarding to designing and building a little opto-isolated serial interface cable.

    The board that I am trying to interface to my pc with has 6 pins.

    Pin1 - (RxD Positive).
    Pin2 - (RxD Negative).
    Pin3 - (TxD Positive).
    Pin4 - (TxD Negative).
    Pin5 - (Ground).
    Pin6 - (+12 Output).

    Pins1&2 are connected to a CNY17-3 Optocoupler via a 100R resistor.​

    Pins3&4 have a 0-12volt signal output.

    What is the best way to go about making an interface cable to connect from my PC's RS232 (com) port to the above board?

    Thanks for your time.

    Best Regards.
     
    Last edited: Mar 29, 2011
  2. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,790
    There are at least two problems with your concept

    1. You have no voltage source on the PC side to drive the TX diode
    2. Most PC's no longer have native serial ports
     
  3. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    I got it working in the end, and this is what I came up with.

    [​IMG]
    Best Regards
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,790
    So where does the +5V come from on the "serial Interface cable" and how exactly do you mount a chip to the cable, or is it a small PC board?
     
  5. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    At this point in time I have made it on my breadboard, and is being powered from a bench psu.

    I have read that it might be possible to power it via the com-port RTS pin, but I have not yet tried that.

    Next stage is to make the pcb board for it.
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    What will this device be used for? Also do not depend on taking power from the serial port. You are going in the correct direction. But as I see it now it is something that is not optional with your design. An important question is. In the final version. Where does the RS232 front end get its power from?
     
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