Hi, I designed (but never used) this timer circuit to control the fans in my PJ.

I'm just putting it here in case it's of some use to someone.

Click to view attachment

R1 consists of a variable resistor and a fixed resistor. And allows you to control the time period the fans stay on for. The circuit is triggered when it's own power supply is connected.

To determine your timing components (R1 and C1) use this formula:

T (Time period) = R1 * C1

Remember, R1 is actually the VR + the Fixed Resistor value added.

Thanks for the share.

This might be better suited to the "Technical Drawings, Designs and Templates" section of the forum.

Perhaps a Mod can move it.

Nice, good old 555 timer circuit. Looks pretty much standard.

Yep. Nothing special, just thought it may come in handy for some people who aren't familiar with these kinds of timers.