Pulse generator from Power-on state?

[Joe in Bendigo]

Hi,
can someone enlighten me how I could create a single pulse (12V DC - about
100ms long) from a state change of a 12VDC voltage? In other words, I need
to create a single pulse when the power comes on and also when it goes off
(the hard bit - for me). I guess somehow the pulse could get generated
easily enough when the power comes on (eg the time it takes to charge a
capacitor), but to make a pulse when the power goes off would require
something to allow that (or another) capacitor to briefly discharge....
Anyway, I'm WAY out of my depth!
Can someone draw me a little circuit to do this to build, please?
Cheers,
Joe
(remove -spam- from e-mail to reply)

 

[Robert Monsen]

Joe in Bendigo wrote:

Hi,
can someone enlighten me how I could create a single pulse (12V DC - about
100ms long) from a state change of a 12VDC voltage? In other words, I need
to create a single pulse when the power comes on and also when it goes off
(the hard bit - for me). I guess somehow the pulse could get generated
easily enough when the power comes on (eg the time it takes to charge a
capacitor), but to make a pulse when the power goes off would require
something to allow that (or another) capacitor to briefly discharge....
Anyway, I'm WAY out of my depth!
Can someone draw me a little circuit to do this to build, please?

You want a signal that is at 0V, except it's 12V for 100ms after either
another monitored signal goes high or low, is that right? Can you power
the monitoring circuit separately, or does it need to take it's power
from the monitored signal?

Whats the pulse going to be driving? How much current will you need to
pull from it?

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.