Camera board • Re: Measuring ̶P̶C̶ fan speed with camera

OK, I did measure fan speed with camera again.
Why?
Because I wanted to know whether fan speed reported for my new Pi5 active cooler is correct:
viewtopic.php?t=359624#p2157364

Now that I have the Pi5 (in KVM setup), I learned a lot on how to get active cooler fan spinning very fast with >9000rpm.
With overclocking to 3000MHz and this special stress-ng command:
I connected today a camera for the first time to my Pi5, and Pi0 camera cable worked.
But my GS camera was too close to the active cooler fan.
I found a connector I bought years ago, that allows to connect flat ribbon cables.
With that and a normal short cable in addition, GS camera had enough distance to the fan:
I did the 3000Mz overclocking measurement first — if I can measure that, I can measure at lower fan speeds as well.
Fan speed >9000rm means >150rps, so high framerate video was needed.
I looked for the options, and decided to go with 688x136@402fps:
https://stamm-wilbrandt.de/en/forum/GS/

GS camera just worked with libcamera-vid.
So I only needed to install GScrop tool on my Pi5:
https://gist.github.com/Hermann-SW/e604 ... 4e0e9f6b9c

Then I did a few test recordings for making camera 688x136 frame record the fan as I wanted.
These recordings were done without 5th shutter time arg, so that the videos were bright.
The real 5000ms recordings were done with 100µs shutter time:These recordings are just dark without a very very bright light.
I used Flashlight app of my smartphone.
But the led had to be moved very close to the fan, in order to be able to see something.

Before I did first real video, I used a water proof red pen for a marker point near fan center.
Then I did record with above GScrop command, and extracted frames with ffmpeg:
After inspecting the frames I got with "eog" image viewer, I used "togg" and "pngs2anim" tools to create 1fps animated .gif:
viewtopic.php?t=288576

And here is the 9100rpm reported in "/sys/devices/platform/cooling_fan/hwmon/*/fan1_input" animated .gif:


So what is the measured speed?
If you start counting when red marker is in 12 o'clock position, it takes 7 frames until marker is again there.
And 4 left turn rotations are done in that time.
So measured fan speed is:Reported fan speed in "/sys/devices/platform/cooling_fan/hwmon/*/fan1_input" is only 9100/13783=66% of real speed.


OK, this was with 3000MHz overclocking, and that probably does not have to be right.

Next I rebooted into 2400MHz default CPU frequency.
Same "speedest-ng" command as above did "only" show 4900rpm in "/sys/devices/platform/cooling_fan/hwmon/*/fan1_input".
I did capture and process video as above, this is the final animated .gif:


If you start counting when red marker is in 12 o'clock position, it takes 11 frames until marker is again there.
And 3 left turn rotations are done in that time.
So measured fan speed is:Reported fan speed in "/sys/devices/platform/cooling_fan/hwmon/*/fan1_input" is only 4900/6578=74% of real speed.


I did the measurements with expectation that reported fan speed is correct.
Even without overclocking reported speed is only 74% or GS camera measured speed.

This is not really serious, but it is a bug.

Statistics: Posted by HermannSW — Thu Dec 14, 2023 9:47 pm

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