Re: smart fans
On Sunday 22 August 2021 17:04:06 Gene Heskett wrote:
> On Sunday 22 August 2021 12:46:14 Polyna-Maude Racicot-Summerside
wrote:
> > On 2021-08-22 10:02 a.m., Emanuel Berg wrote:
> > > tomas wrote:
> > >> I disagree. The thing poses [1] as a DC motor (2 pins power,
> > >> one tacho). I don't think you get too much control over RPM
> > >
> > > That's what you get with the 4th wire/pin? A sensor to
> > > read RPM?
> >
> > Opposite
> > 3 wire = 2 wire to drive motor + 1 wire to get speed
> > 4 wire = 2 wire to drive, 1 to get speed, 1 to modify speed
>
> I as a CET, am totally unimpressed with the miss-information being
> thrown about in this thread. A total lack of how its actually done in
> real hardware.
>
> 1. Any si diode, passing a few microamps of fwd current, is in fact an
> excellent, does not need to be calibrated, thermometer capable of 1
> degree C accuracy. There are several million candidates buried in
> todays cpu's.
>
> 2, even a 2 wire fan can be controlled by using this voltage to
> determine the on time of a small transistor. Often down to 1% speed at
> room tmps, so other than the cost of the time at die bondout time, its
> free. The 1% minimum is actually used to help distribute the motors
> lubricant.
>
> 3, boiled down, the temp measured by this diode can be scaled to
> control the fan to maintain the device being monitored at a fixed
> maximum temp, and its done on 2 or 3 of the gates on the cpu die
> intended to be used to replace a bad gate in you cpu. Intelligently
> done at test and bondout time, it might add 10 seconds to the time
> needed to verify the rest of the chip.
>
> > > "What you can't measure, you can't control"
>
> Better, if you can measure it, you can control a 2 wite motor.
>
And I knew I couldn't get by without a typu. s/b wire.
In fact, if a motor has 3 wires, there is a good chance its a tacho wire,
used ONLY to tell /you/ how fast its running.
> Cheers, Gene Heskett
Cheers, Gene Heskett
--
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