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Need a RS232 PCI card that works with optos

Discussion in 'Embedded' started by Rumpelstiltskin, May 26, 2009.

  1. I have test equipment with optically isolated RS232 ports.
    Seems modern RS232 ports do not support +/-12V.
    They all seem to be less than +/-8V, many only +/-5V.

    Anybody know of a cheap source for +/-12V RS232 PCI serial boards?

    What ever happened to 1488/1489 serial drivers?
    Rumpelstiltskin, May 26, 2009
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  2. A +/-5 V transmitter is not RS-232, a transmitter generating +/-6 V to
    +/-25 V might be RS-232,
    a receiver with threshold levels between +/-3 V is acceptable.
    These chips require some uncomfortable voltages like +/-15 V, which
    are not readily available in current 5 or 3.3 V systems.

    Paul Keinanen, May 26, 2009
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  3. [Apologies if this is double posted]

    RS232 minimum voltages have progressively got lower with each new
    revision of the standard. Now +/-5V is the minimum. From memory
    that is at the receiver end though, so if a card is only giving 5V
    that doesn't allow anything for losses but it is still within spec.

    Have you considered dropping in an active buffer between the PC
    and the isolator? For moderate speed RS-232 this needn't be
    difficult. Back of an envelope calculations show a TL084 used as
    a comparator will slew plenty fast enough over 24V for 38400,
    though you will probably want to artifically lower the input
    impedance to give a degree of noise resistance.

    Of course, the driver will be fairly simple to knock up, but
    providing a +/-15V supply is going to be cumbersome.
    Andrew Smallshaw, May 26, 2009
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