> > >Longest RC time delay -> latch reset
> > >Shorter RC time delay -> data in
> > >No RC time delay -> clock

When I was a student and lived in a caravan I had to go to the lavatory
outside at night. I feared the door falling in the lock behind me and me out
in the cold with the key insde, so I built an electronic lock with a single
pushbutton switch. It use two 4000 series ICs (I don't remember which) and
some diodes. The one I built worekd very reliable, but I have my doubts
about reproduceability. The principle was to derive a clock from a delayed
rising edge of the input, so if the input went down quickly it would clock
in a 0, otherwise a 1. No reset, clocking in 8 data bits this way was enough
challenge. Just to be sure I hide an override button somewhere, and I also
buried a spare key. I guess I w as fit for 3-fail-safe space work even
then...

Wouter van Ooijen
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Van Ooijen Technische Informatica: http://www.voti.nl
Jal compiler, Wisp programmer, WLoader bootloader, PICs kopen

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