how to make a 3minutes delay

[Lac]

I'm building a cooling circuit for my projector, where the fans will be running for 3-5 minutes after the projector has been shut off to draw out all the hot air. The first solution i came up with included a microcontroler which controled a relay. I'm able to write the code myself, but i would like some help creating the delay-loop, anyone?

And are there any better/easier solutions to this "problem" than this?

Cheers!
Lac.

 

[Nigel Goodwin]

I'm building a cooling circuit for my projector, where the fans will be running for 3-5 minutes after the projector has been shut off to draw out all the hot air. The first solution i came up with included a microcontroler which controled a relay. I'm able to write the code myself, but i would like some help creating the delay-loop, anyone?

And are there any better/easier solutions to this "problem" than this?

It's an ideal job for an 8 pin PIC, you can generate delay loops using the delay code generator on the PICList - just tell it how many seconds you want, what your oscillator frequency is, and press the button!.

 

[John Sorensen]

Since the amount of time is not critical, why not just use an R-C circuit into a comparator. Or even a thermistor to cycle the cooling fans as needed when it's turned off.

j.

 

[Oznog]

This may be a silly question, but why do you want to keep cooling a processor for 3-5 min after it's not generating any more heat? I see no benefit to being in such a hurry to get it down to room temp.

 

[Lac]

not a processor but a projector, you see that inside the projector (which is enclosured) there is a 400W lamp pluss some ballast, that generates a huge amount og heat, nearly 80 degrees. And if the fans stop running the hot air would "pile up" inside the projector, and eventually the temperatur would rise even more, which is not good! :?

Hope you got it.

 

[williB]

I would suggest an 8 pin pic as Nigel suggested with a thermistor as input as john suggested.
i also like John's suggestion of a thermistor hooked up to a comparitor.
i have one running 24/7 on my fridge .. Fans comes on when the fridge comes on and go off about two mins after the fridge goes off..
i have saved tons of money with this circuit, because i can remember when the fridge would be running for an hour at a time in summer...
this past summer it would come on ...and go off as it should .

 

[alamy]

It's an ideal job for an 8 pin PIC, you can generate delay loops using the delay code generator on the PICList - just tell it how many seconds you want, what your oscillator frequency is, and press the button!.

code generator : https://www.golovchenko.org/cgi-bin/delay, thanks nigel..