On 5/13/06, Spehro Pefhany <speff@interlog.com> wrote:
> At 12:38 PM 5/13/2006 +1200, you wrote:
>
>
> >Tell us how you are trying to do an unknown thing and we may not be
> >able to help.
> >Tell us what you want to achieve and we'll tell you how to achieve it.
> >         RM
>
> I think what he wants to do is to take an audio signal (line level?)
> and modulate a fan controller based on the expected power dissipation
> in an audio amplifier, so that the fan tends to be quiet when the
> music is quiet, and loud when the music is blasting.


This simple trick and needs one: transistor, termistor (Kohm range),
resistor, capacitor, ventilator.

Thermistor is sensing the radiator's temperature on which final
transistors are mounted. Transistor's load is a low current ventilator
connected from colector to Vcc, an RC from the transistor base to
ground and the thermistor from base to Vcc. Heating the termistor will
decrease his resistance so the transitor will be turned ON and the
ventilator will blow faster. It's a common scheme used in many
computer power supplies.

Vasile



>
> Something like a precision rectifier (couple of op-amps) into a PIC ADC
> and PWM output would fill the bill. The front end might not have to be
> than complex, of course.
>
> >Best regards,
>
> Spehro Pefhany --"it's the network..."            "The Journey is the reward"
> speff@interlog.com             Info for manufacturers: http://www.trexon.com
> Embedded software/hardware/analog  Info for designers:  http://www.speff.com
> ->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff
>
>
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