At 07:58 PM 5/26/02 +1000, Roman Black wrote:
>Dwayne Reid wrote:
> >
> > Glue is 2 Rs, 2 Cs and 2 diodes - the diodes could be eliminated if you
> > were willing to ensure that the rest time between bits and bytes was long
> > enough to completely charge or discharge the RC delays.  I wouldn't bother
> > - adding the diodes costs hardly anything.
>
>
>I love these "cheap" challenges! I would be so daring
>to suggest that you COULD do it with just one serial latch
>chip (serial in parallel out shift reg) and two RC networks.
>You only need one serial input line.
>
>Longest RC time delay -> latch reset
>Shorter RC time delay -> data in
>No RC time delay -> clock

The problem with using just a cheap shift register is the limit on rise and
fall times on the clock inputs - most require rise and fall times to be
faster than 500 ns.  As I mentioned in my earlier post, some higher end
shift registers do have schmitt trigger inputs but those tend to cost much
more than a cheap SR (4021) and 2 sections of a hex inverter schmitt
trigger (4584 or 40106).

dwayne

--
Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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