Quoting James Nick Sears <lists@jamesnsears.com>:

> I'm working on a one-off project that is controlling a pair of 90VDC
> motors through Minarik drives (thanks to the list for the earlier
> tip).  It's going to be entirely unsupervised, so just to ease my mind
> I'd like to have some sort of watchdog IC controlling the AC power to
> the motor controllers (through a relay), so that if the IC doesn't get
> the periodic signal from the PIC it will cut the power to the relays
> indefinitely until the microcontroller is brought back online by other
> means and the IC once again receives its watchdog pulse from the micro.
>
> This last part seems to be the catch.  What I'm finding is no shortage
> of ICs that generate a reset pulse on a failure, but I want one that
> holds an output high (or low) until the failure is corrected.  I
> figure I'll use the PIC's internal watchdog to reset itself, but I'd
> like this extra measure of safety to make sure the moving parts don't
> destroy themselves in the event that the PIC should completely fail.
>
> Any suggestions?

You could latch the pulse with a flip-flop.

Best regards,
Spehro Pefhany
-- 
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