Heaven forbid, I had to design a simple circuit, but this time I
couldn't use a PIC. It would be an ideal little job for a 508 but I
don't have one handy.

The circuit needs to have a relay operated when power is applied, but
when it gets a -ve going 1/2 second pulse, let the relay stay operated
for another 40 seconds then release it permanently.

The software would be quite simple, but what a brain strain going back
to discrete digital again to accomplish the same task when I haven't
fiddled with TTL or 4XXX CMOS for what seems like ages.

I ended up using 3/4 of a 4093 quad NAND gate. It's amazing when you are
out of practice, how long it takes to come up with a simple solution
without software.

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Best regards

Tony

http://www.picnpoke.com
mailto:sales@picnpoke.com