[denny800]

Are you saying that the diagram in post #10 is the correct one? Hooked up that way the fan runs all the time and olny slows down about 5% when the sensor activates.
Thank you.

[DanielF]

I somehow missed the entire Page 2 of answers to your question, which changes a few things.

Had the fan been 5V, then the second circuit in your post #10 would have been the only one of the two that could work. But now I see that the fan is 12V, so it won't work either.

And finally you're confusing me by saying the fan only slows down when the PIR detects something.

Do you want the PIR to start or stop the fan?

When you've answered that, I'll post a new circuit diagram for you that should work. Keep in mind you'll need both 4.5V and 12V power supplies (actually, a power supply from a discarded PC would be ideal, having both 5V and 12V outputs available).

Daniel

[KISS]

Daniel:

How did I miss all of that? Fan 12 V. PIR 5V.

How about the ULN2003 http://www.datasheetcatalog.org/data...2qsaii8o3y.pdf

I like the chip. It does contain the diode and rated for 500 mA the fan is 300 mA.

A 5V regulator like the LM7805 and only a 12 V supply?

This assumes that the PIR comes on when people are present.

[DanielF]

OK, I gather from your earlier post that you want the fan to come on when movement is detected. The following circuits should achieve that. Note the requirement for two supply voltages (+5V and +12V, with a shared common labelled 0V).

If you want to use just a single 12V supply, follow KISS's suggestion of a 78L05 regulator from the 12V supply to feed the PIR sensor.

Due to this website's stupid size limitation, I've had to rotate the drawing 90° – you can rotate it back after downloading.

Daniel

[KISS]

Yep. Thanks Daniel.

The UF4001 can be a 1N4001 diode which Radio Shack will have.

[denny800]

I changed your "will work" diagram to using a 12 volt supply only. I think I'm on the same page?

[KISS]

I also would add a 0.1 uf polyester film cap close to the regulator from IN to ground and one from OUT to ground. It helps keep the regulator stable.

[DanielF]

Denny,

The 78L05 is not a transistor (though physically it looks like one), but an integrated circuit regulator. I've redrawn it correctly for you, and added some desirable 'stability' capacitors and protection for the MOSFET.

Note that the pinout for the 78L05 is different from the 7805, so if you decide to use the (larger) 7805, check its datasheet for the correct pinout.

Daniel

[KISS]

D4 is a 10V Zener diode such as Digi-Key - 1N5240BFSTR-ND (Manufacturer - 1N5240BTR)



Daniel, why did you put C1 to PIR Out rather than ground?

[DanielF]

Oops, thanks KISS. Corrected circuit attached.

Daniel