In need of a circuit - 12V DC Hold on for x-seconds

[lytnin]

Hi All,
Long time no speak.

I'm looking for a 12V DC circuit I can trigger through an opto & mosfet (unless you have a better suggestion), that will stay on for 'x' amount of time (adjustable preferably) regardless of the trigger state.

Trigger voltage is about 3.5V

Example.
A quick pulse, either through Vixen/Lor or a momentary switch etc, that will turn on the circuit which will run a relay or some revolving lights for 15-30 seconds. Additional pulses while the circuit is running should not reset the start time.

Any thoughts would be greatly appreciated.

Cheers

[mrpackethead]

Hi All,
Long time no speak.

I'm looking for a 12V DC circuit I can trigger through an opto & mosfet (unless you have a better suggestion), that will stay on for 'x' amount of time (adjustable preferably) regardless of the trigger state.

Trigger voltage is about 3.5V

Example.
A quick pulse, either through Vixen/Lor or a momentary switch etc, that will turn on the circuit which will run a relay or some revolving lights for 15-30 seconds. Additional pulses while the circuit is running should not reset the start time.

Any thoughts would be greatly appreciated.

Cheers

Many ways of doing this.. These days i'd probalby take a small pic.. alternatively you could use a 555 timer, but its just as easy to use the pic..

[Matt_Edwards]

555 is probably the easiest.

PIC or AVr would be a snack also, but will require voltage regulator.

What are you driving? Relay?

Cheers
Matt

[lytnin]

Yes Matt, a relay which will in turn be running revolving lights or strobes. 555 would be easier, so any circuitry would be great.

btw, Might have to come and see you since you're only around the corner - lol

Cheers

[Matt_Edwards]

any time.
555 monostable cct can be found here (http://www.kpsec.freeuk.com/555timer.htm#monostable)
they can drive a relay directly as shown here (http://www.kpsec.freeuk.com/555timer.htm#output)

infact I think Jaycar's kit KJ-8202 (http://jaycar.com.au/productView.asp?ID=KJ8202&CATID=25&form=CAT&SUBCATID=695) will probably do what you want

Cheers
Matt

[lytnin]

Thanks Matt,
That Jaycar kit, looks like it waits x amount time before activating the relay, rather than turning it on for x amount time.

The monostable 555 with relay looks like it'll do the trick nicely. So the next question is how to use an opto/mosfet to activate it?

Cheers

[P. Short]

http://hauntforum.com/showthread.php?t=18387

This guy has a diy 3-stage timer design...first stage is the delay before activation, second stage is the on-time, third stage is the delay preventing re-activation.