> > Opto couplers are cheap and simple. It's highly unlikely that the LEDs
> > will light except when driven by the switch closures.
>
> Oh yeah?  I have heard of just this happening in an Automotive
> environment (big long truck actually). The trick is to put zeners in
> series with the optocouplers so they need a signifcant current AND
> a significant voltage before they light up. Have seen this in other
> commercial equipment too where a certain amount of induced EMF
> is practically unavoidable. Hope this helps.
>
> Brent Brown

With some serious bypass caps, 10nF are useless, even 100n dont cut
the grade in this sort of environment, I prefer 470nF.Beware
electrolytic caps above this value that are not low ESR.
 I have seen LEDs actually flashing from induced noise with motorized
gates limit switch contacts running next to the power wires. That
problem was fixed with the afore mentioned caps AND a 470 ohm
resistor across incoming pair .... brutal but effective.

Power Distribution and Radio Comms are youre biggest problems in this
environment as far as noise goes.

_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

www.psych.auckland.ac.nz

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