Need help to build a fan timer

Hi,

I need a schematic for building a fan timer. I'm currently building a hushbox for my projector, and the hushbox is equipped with a fan to ventilate the hot exhaust air. My projector has an output trigger signal that goes high whenever the projector is switched on, which I will use to start the exhaust fan via a relay. When the projector is switched off, the trigger signal goes low and the exhaust fan stops.

I need a timer circuit that will keep the fan going for another 3-5 minutes after the projector has been switched off, so that the projector is properly cooled. I think this kind of circiut is built-in in many bathroom fans.

Anyone out there with a schematic? Thanks in advance

You don't say what the relay operating voltage is, but assuming that it is 12 volts, this circuit should work.

Fan timer

I question the component values on pins 6 and 7. Actual timing for the 555 timer in this configuration is T=1.1RC. In this case 1.1 x 470k x 10uF = 5.17 seconds.

So you know the formula for working out the timing components, adjust the component values accordingly to obtain the appropriate timeout.......

Thanks a lot

Thanks a lot for the help! The operating voltage of my fan is 12 Volt, which I should have mentioned earlier. All I need now is to trim the component values!