Jean Delvare wrote: > On Sat, 09 Jun 2007 18:40:06 +0100, Phil Endecott wrote: >> It's clear that the right frequency to choose will depend on the >> particular hardware, but I don't think we'll find anything where 187 >> kHz is a good choice. It could perhaps be considered bizarre to choose >> a default based on what I found worked with my unique home-made >> hardware :-) Jean, you must have written a script to get the numbers >> in that graph; if you post it, perhaps other people can try it out and >> we can see if there is a consensus? > > I published my script here: > http://khali.linux-fr.org/devel/lm-sensors/draw_pwm_response.pl > It writes the results to a CSV file, it's up to you to make a graph out > of it (I think I used OOo calc). Mine is here; I modified your script a bit: duty cycle increases on the X axis, it uses a different range of PWM frequencies, and I plotted it using gnuplot: http://chezphil.org/tmp/fanplot.png Based on this I think I'll reduce mine below 40 kHz, maybe 25 kHz or something like that. >> (The 'other people' don't need to >> be F71805 users since it's mainly measuring the characteristics of the >> fan itself.) > > This would be true if all the chips had perfectly square duty cycles at > all frequencies, but you found out yourself that this isn't the case > for the F71805F at high frequencies. Anyway, I suspect that fans are too > different and we won't find a frequency which pleases everyone. The effect we're seeing is due to the fan and the driver-transistors. All chips will have essentially identical outputs at their pins, which will look nice and square. > I confirm that I didn't modify my board in any way, maybe it includes > some additional circuitry. The problem isn't totally fixed though, as > you can see on the graph, below 1000 RPMs I lose the fan speed readings > (there were a couple bogus values which removed from the graph to make > it clearer.) Is it even worst on your side? Are you sure that it was a reading problem, not that the fan had actually stopped? I could believe that fans have a minimum speed below which they don't have enough rotational momentum to get past the "dead points" in the magnetic field. As you can see, my fan runs down to a few hundred RPM. I haven't experimented further with that. I will follow up on the other points over the next few days. (Progress will be slower, I have other things to do during the week.) Regards, Phil.
