Comments on: A Proportional 12V Fan Controller

By: johnarthur

johnarthur — Mon, 30 Mar 2009 01:48:33 +0000

It sounds as though it is basically OK. You may be being misled by the length of time it takes to react to things; it takes tens of seconds for it to appreciably slow down or speed up – or come to a stop. If you put a DMM on the 1uF capacitor and cool the LM34 to 64F you should see the average voltage slowly falling there until it gets to about a 20% PWM at which point it will turn off. At worst you could try disconnecting the LM34 and using a 10K pot instead to generate voltages in the .32 – 1V range to see how it behaves.

By: David

David — Mon, 30 Mar 2009 01:29:42 +0000

OK I double and tripple checked the circuit and there is a PWM signal on pin 2 regardless of the temperature on the LM34. I ran the LM34 down to 64 degrees and observed .643 volts on pin 7 but the PIC code still continues to generate a PWM signal. Pin 3 and 6 are high and pin 5 is toggling indicating the PIC code is executing. I also disconnected pin 2 on the PIC from the circuit and momentarily applied 5v to the 10K resistor on the side that was connected to pin 2 and the fan executes and full rate. Once I momentarily ground that same side of the 10K resistor, the fan stops running. I am using the PIC code unaltered from your web site. Any suggestions would be greatly appreciated.

Thanks,

Dave

By: johnarthur

johnarthur — Sun, 29 Mar 2009 22:33:26 +0000

To the 12V rail. Sorry, that really should have been in the circuit diagram…

By: David

David — Sun, 29 Mar 2009 22:29:43 +0000

Doe the LM358 power get connected to the +12v or +5 volts?

Thanks,

Dave

By: johnarthur

johnarthur — Thu, 05 Mar 2009 06:20:55 +0000

The fan aims to keep the temperature below the constant kTargetTemp which equals 160 / 2.04 = 78.5F. This should be the temperature at which the fan will start running. Inaccuracies in the LM34, however, mean it could be anywhere between 74 and 81F. You might need to test your particular setup and tweak kTargetTemp to suit.

By: David

David — Wed, 04 Mar 2009 13:59:20 +0000

Your articles are very helpful. I have built an IP weather camera that is hidden in a bird house and I am rigging up a fan control circuit to keep the internals cool especially for those hot summer days and your proportional fan controller circuit is great. At what temperature does the fan beging to operate?

Thanks,

Dave

By: Pasan

Pasan — Thu, 10 Jul 2008 11:16:13 +0000

This is awesome

Thank you

By: rui

rui — Wed, 18 Jun 2008 12:19:27 +0000

the controller is now working properly.
thanks for help.

sorry for the delayed reply

By: johnarthur

johnarthur — Sun, 04 May 2008 08:11:30 +0000

I have uploaded an archive of the project to:

http://www.mediafire.com/download.php?mi0dttdkmdm

I hope this solves your problem.

By: rui

rui — Sat, 03 May 2008 21:52:51 +0000

Your controller is just what i’m looking for
infortunently, wen I put the code in mplab there are errors to eliminate. some diferences are in characteres, mabe because my software is configured to portuguese.
I appreciate if you send to me the .hex code and/ or the .asm file

rui