Need a little help building a 12 volt timer

[Richard Henry]

Back in my days at the university one of our professors used to joke
that the quality of a digital designer is inversely proportional to the
number of one-shots he or she uses. Now I don't quite agree with that
and I use them a lot myself, even though they will be "home made" rather
than a 555 or HC123. It's just that the cost picture changes with longer
timings and cost is usually the predominant factor in a commercial design.

I once saw the a digital filter that was based on one-shot timers. A friend
of mine was given the project to redesign after the origianl designer had
been encouraged to seek employment elsewhere.

 

[Joerg]

Hi Richard,

I once saw the a digital filter that was based on one-shot timers. A friend
of mine was given the project to redesign after the origianl designer had
been encouraged to seek employment elsewhere.

Or phase shifters made from prop delays on chips. Yeccch. I ripped out
that whole circuit and replaced it with an analog solution around the
SD5400. Lots of frowns at first because it was the only analog portion
on a large digital board. They really liked it once they realized that
it reduced cost big time and was totally reliable. The real joy set in
when the phase jitter was gone. Well, it wasn't really gone but went
from outrageous to barely measurable.

Regards, Joerg

 

[Tam/WB2TT]

Hi Richard,

Or phase shifters made from prop delays on chips. Yeccch. I ripped out
that whole circuit and replaced it with an analog solution around the
SD5400. Lots of frowns at first because it was the only analog portion on
a large digital board. They really liked it once they realized that it
reduced cost big time and was totally reliable. The real joy set in when
the phase jitter was gone. Well, it wasn't really gone but went from
outrageous to barely measurable.

Regards, Joerg

Yoerg,
I have been down that path. Bottom line is that the factory hated it because
they couldn't test it on their bed of nails gizmo.

Tam

 

[Joerg]

Hi Tam,

I have been down that path. Bottom line is that the factory hated it because
they couldn't test it on their bed of nails gizmo.

They can but it requires the guys who set up the tester to understand
what they are doing. Plus maybe a few minutes of help from an analog
engineer. Nail bed testing is pretty much passe these days, at least
with my clients. In the 80's when it was done more we tested a lot of
analog boards with it. We had to measure pulse responses in a rather
bizarre way to make a fault or no-fault determination and figure out the
location of a questionable part. Sometimes we even had to design small
gizmos that would be hooked up between pins and tester.

Nowadays most circuits are either so low cost that it isn't worth to
find the cause of a board failure or they are self diagnosing. Also,
with dense SMT the nail bed method become less and less feasible. There
just isn't any space to place the nail landing patterns.

Regards, Joerg