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PISO register to serial port

Discussion in 'Electronic Design' started by graffy76, May 11, 2006.

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  1. graffy76

    graffy76 Guest


    I'm trying to get a device with 64 outputs (24 VDC) to communicate with
    PC through it's serial port. I realize I need to use parallel-i
    serial-out shift registers to accomplish this, but there's a coupl

    First, the output side of the circuit is borrowed from Bill Bowden's pag
    for his (PC Serial Port Reciever) circuit. It runs fixed at 9600 baud an
    uses two stop bits. As far as I can tell, that means I'll need to us
    11-bit hift registers.

    Second, once the data's been clocked out of the registers to the port, th
    zero-voltages need to be converted to -10 volts and the +5 volts need to b
    amplified to +10 volts. Does anyone have any circuits or examples that ca
    do this?


  2. Paul Burke

    Paul Burke Guest

    Just program up a small microcontroller. For 64 bits of input, you'll
    need either multiplexers or shift registers. For a SR load them all in
    parallel with one output line, shift clock on another. Or have 8
    parallel SR chains if your controller has enough IO, only one clock per
    set needed. Shift in groups of 8, slap them into the UART transmit
    register (that adds any start/ stop bits), use MAX232 or equivalent on
    the output. I don't know Bill Bowden's page.

    Paul Burke
  3. graffy76

    graffy76 Guest

    Bill Bowden's Hobby Circuit website:

    There's a link to the PC Serial Port Reciever on that page. Actually,
    was hoping to pull this off without using a microcontroller because I'v
    never used them to build a circuit... I suppose that's not very likely a
    this point.

    I was planning on using serially-linked PISO SR's to do the job. Th
    trick is building eight bytes - without a microcontroller, the only way
    could see it done is in the SR's themselves...
  4. Why don't you use a parallel port? Then you just need a few SRs, a 5V
    supply (can be derived from the PC with a drive connector) and some
    bypass caps. Plus some stuff to get the 24V inputs down to 5V (I
    suggest quad channel optoisolators with appropriate input networks and
    output pullups). Pretty simple, and no microcontroller required.

    Best regards,
    Spehro Pefhany
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