Re: Looking for a Low Cost On Delay Timer

["Guv Bob" <guvbob2003@xxxxxxxxxxxxxxxxxxxxxx>]

"unruh" <unruh@xxxxxxxxxx> wrote in message =
news:WxsTt.233047$Z84.231177@xxxxxxxxxxx
> On 2013-08-28, Guv Bob <guvbob2003@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> > "unruh" <unruh@xxxxxxxxxx> wrote in message =
news:lAHSt.180556$po1.28313@xxxxxxxxxxx
> >> On 2013-08-26, Guv Bob <guvbob2003@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> >> > "Guv Bob" <guvbob2003@xxxxxxxxxxxxxxxxxxxxxx> wrote in message =
news:1_udnQ7rBpNjRo7PnZ2dnUVZ_sidnZ2d@xxxxxxxxxxxxxxxx
> >> > Names can be confusing, so here's what I'm doing....
> >> >>
> >> >> http://img43.imageshack.us/img43/7434/wvm.gif
> >> >>
> >> >> When 12VDC is applied to the input, I need a 12VDC output for 5 =
seconds.  Then output will go back off and stay off until the input goes =
to zero.  Then cycle starts again.
> >> >>
> >> >> Current for both legs is in the 10-50ma range.
> >> >>
> >> >> A simple on-delay timer would work but I'm having trouble =
finding one with NC contacts.  Tons of stuff $100+, but for this =
application, it has to be under $20.
> >> >>
> >> >>=3D=3D=3D
> >> >
> >> > Thanks for all the tips and good info.  I had wanted to put =
something together from components but my brain is too far behind these =
days.  I'm going to give this a shot and hopefully I'm not picking the =
wrong one.  It's $5 at Frys...
> >> >
> >> > Velleman MK111
> >> > =
http://www.vellemanusa.com/downloads/0/minikits/manuals/manual_mk111.pdf
> >>=20
> >> Except that looks like an oscillator rather than a "oneshot"=20
> >> You said that you wanted something that if the input was larger =
than 5
> >> sec, the output would go high for 5 sec, and then drop to 0. If the
> >> input droped before 5 sec was up, you wanted the output to drop as =
well.
> >> Then you wanted it to wait until the input went high again before =
doing
> >> that again.
> >> This device has a relay (why would you need a relay for 50ma? Most =
ICs
> >> can handle an ouput current of 50mA at 12V without the need of a =
relay.
> >>=20
> >> This kit is an oscillator, where you can adjust the time it is on =
and the
> >> time it is off with the pots. It has no input.=20
> >>=20
> >> It uses a 555 timer chip. The primary design of the 555 is to =
initiate a
> >> pulse when the input goes high, and stays high for the requsite =
time
> >> even if the input drops again. If the input stays high beyond the =
time
> >> Ie, I think you want to think your way through what you need =
carefully.
> >
> > Thanks, yes you're right.   What value resistor could I substitute =
for RV1 to give a pause time between pulse to 10 minutes?
>=20
> RC=3Dt roughly. (depends on exactlywhee in the charge/discharge cycle =
the
> thing triggers). But R probably should not be much over 1Mohm, as
> otherwise the input resistance of the ic becomes important.=20
> Then C should be about 600uF (probably not electrolytic as the =
internal
> resistance can become important but finding anything else at that size
> is pretty impossible)

Thanks.   I think I'll put a fixed 2M ohm in series and see if I can get =
a 3-5 minute range.