At 03:02 PM 7/11/2003 -0400, you wrote:


>Even 10Hz circuits are really much more than 10Hz if the contain digital
>signals.  After all, the power supply transients that the bypass caps help
>to reduce are the result of the switching edges, not the steady state
>between the edges.  A "10Hz" circuit may have fewer edges per second, but
>any single edge can cause trouble without proper bypassing.

I had to fix a slapdash timer design that ran at a few Hz. *Some* units
would bang back and forth a few times at every edge and screw up the timing,
over *some* of the temperature range. The worst kind of engineering goof-up,
poorly designed, but it *appeared* to be okay, the guys in charge said
"ship it" and then the returns (several percent, which was a lot of units)
started coming in from Timbuktu and everywhere.

They had a bit of warning- a 5%+ fallout rate at assembly, but didn't
investigate it until it was too late.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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