Jet Jockey/A4 Pilot

I'm looking for a switch that once activated will remain on for a pre-determined time, lets say no more than 3 seconds. In other words I want to deactivate a system for no more than 3 seconds. Once the switch is activated the affected system drops off line for 3 seconds and afterward comes back on line. The switch would have to be small enough to fit somewhere in our cars, near the dash and it would have to look good, not shaby.

xr4tic

you could probably design something using a 555 timer.

Jet Jockey/A4 Pilot

What is and where can I get a 555 timer?

ModifiedA4

its an IC...availible at radio shack.

®ob

Radio Shack used to have a book all on the 555/556 timer and sample projects. I think I still have mine buried somewhere

WYSIWYG

the capacitor will store 12v instantly when you push a button(normally OFF), which also toggles the relay switch (turning one (terminal 87) to ON and one (terminal 87a) to OFF). depending on the size of the cap, the system will remain like this until the cap drains to about 5v. try a cap with 1cm diameter, that should hold about 3-5 secs then back to normal (t87 OFF, t87a ON)

ModifiedA4

yup...i have that book...i think they were called "mini-inventors" handbooks or something.

xr4tic

so figure ~ 100 ohms for the coil resistance of the relay.
Vo = 12V
R = 100
t = 3 seconds
Vt = 5V

solve for C

C= .002918, or roughly 2900uF

Radio Shack has 2200uF caps for $4, which should be good for about 4 seconds, assuming my guesstimates above are correct.

robertwroth

Try the autospeed site (same group that makes the intelligent IC controller). They have a timed relay kit that you can adjust the time using capacitors.

WYSIWYG

very good. although i suggest a number of smaller caps for 'adjustability'