Getting back to the original question, it occurs to me that if
you can deal with an inverted output sense (that is, the output
stays LOW until there is a missing pulse), you can probably use
the "traditional" time-delay-from switch circuit (figure 8 from
http://www.uoguelph.ca/~antoon/gadgets/555/555.html )
This applies the trigger signal to the reset pin as well as
the trigger pin.  Some change in component values may be
needed; IIRC, this will charge the cap from 0 to 2/3 V instead
of sticking between 1/3 and 2/3 V...


>> A wild thought: If there exists a small 8-pin micro (PIC or
>> otherwise) with Vdd and Vss on the same pins as the 555, you
>> could swap that in. Assuming its a 5V circuit.
>>
For "traditional" 555 applications, you can fit a pic10f on a little
daughter card that would plug into a 555 socket, with power and
"digital" IO (trigger, output, reset) run to appropriate pins and
others left disconnected.  Indeed, I have several times played with
the idea of developing nice GUI (or otherwise human-oriented) PC
software where you plug in 555-like design parameters and get out
PIC code (or a programmed PIC, for that matter.)

However, you quickly run into the realization that there are MANY
places where even the cheapest microprocessors is NOT a good
replacement for a 555; the micro has very limited drive capability
and power supply limits. for instance, and applications that
are not quite "standard" are distressingly common...

BillW
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