Could also use some software filtering.  For example, maintain a counter
that increments each time a polling routine sees an apparent switch closure.
Reset the counter when the closure goes away.  Only consider it a real
closure if the count reaches some appropriate value.  This way short
duration noise is ignored, but the DC of a real switch closure is not.  This
also effectively debounces the switches.

> 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.

---
                                        Peace,
                                        William Kitchen
                                        bill@iglobal.net

The future is ours to create.