Shift Register noise
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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
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
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!