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Shift Register noise

ArchiverArchiver Posts: 46,084
edited 2000-05-03 17:41 in General Discussion
I need to build a unit that will function as follows:
1) receive an +5v input from a spst toggle switch
2) respond to an ON input condition by sending a +5v output pulse through
a driver to an optoisolator
3) will accomodate 90 inputs and 90 outputs
4) will function in the DC frequency range

My plan is to use shift registers to multiplex the outputs on a basic stamp.

My question is:
1) will I run into noise interference problems if I use a 6' cable to run
from the basic stamp output pins to the remotely located shift registers?

2) Can these problems be overcome by adequate shielding or additional
circuitry?

3) Should I give up, locate the shift registers and drivers next to the
basic stamp and run 90 wires to the remote optoisolators?

Thanks.

John

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2000-05-03 17:41
    John,

    I suggest inserting series resistors of 33~100 ohms at the point where each
    signal enters the cable. This will suppress ringing, hopefully without
    adding too much delay. Also use buffers (or a pair of inverters) at the
    receiving end to square up each signal before feeding it to the shift
    registers.

    One more trick to consider: Use a big LED numeric display driver chip to
    drive your optoisolators-- I think the MAX7219, ferinstance, handles 64
    outputs. Just be aware that those outputs are time-shared!

    >I need to build a unit that will function as follows:
    > 1) receive an +5v input from a spst toggle switch
    > 2) respond to an ON input condition by sending a +5v output pulse
    through
    >a driver to an optoisolator
    > 3) will accomodate 90 inputs and 90 outputs
    > 4) will function in the DC frequency range
    >
    >My plan is to use shift registers to multiplex the outputs on a basic stamp.
    >
    >My question is:
    > 1) will I run into noise interference problems if I use a 6' cable to
    run
    >from the basic stamp output pins to the remotely located shift registers?
    >
    > 2) Can these problems be overcome by adequate shielding or additional
    >circuitry?
    >
    > 3) Should I give up, locate the shift registers and drivers next to the
    >basic stamp and run 90 wires to the remote optoisolators?

    Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
    Manufacturer of the famous BOB-II Serial Video Text Display Module!
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