How can I set a relays, time/duration?

I got a power antenna for my car but it has no brains what so ever. I mapped out a relay system that can power my antenna (up) when the radio is turned on and (down) when the radio is turned off. Problem is duration... the relays switch power but how can I tell the relays to STOP after ~1.5 seconds?

What can I use to control duration?

This may be a dumb question or this may be a hard question, really I just don't know? I do have a good understanding of electrical components so if someone out there can help please tell me what my options are.  Thx

LOL!  Zero replies huh... well I guess this was a bit more complicated than I had originally suspected.

I do realize that relays have no control over duration of time activated but I thought someone might be able to tell me more about how I might achieve this.

Any info would be a big help.

Thank You

-s

You could turn on a relay for a specific time period using a monostable timer circuit.  Triggering the timer with a pushbutton produces an output pulse of fixed time.  Here's a link that shows you how to make a monostable timer using a 555 timer chip....

http://www.doctronics.co.uk/555.htm#monostable

Hi,

Assuming you might find one, older Saabs (from the 80's), had a simple two wire power antenna motor.  These had a control box attached which reversed the polarity to the two wires for a fixed duration, depending upon the radio being on or off.  They were easy to modify  the duration of the time by changing two electrolytic capacitors in the unit.  Saab dealer or salvage yard perhaps.  Also older Audis (80's also) had a similar system. Not sure if this helps, but good luck.

Mark M

The problem is how do you get the antenna Down after the timer times out?

You need a circuit that makes the antenna go up then it times out and when power is removed it switches polarity and makes the antenna go down and time out again.

Why not just use a DPDT switch to do the job? It would be a whole lot easier.