martinrowan
Posts: 63
Joined: Wed Aug 26, 2015 11:00 am
Location: Berkshire, UK
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PoE HAT Fan Hysteresis - Now implemented

Sat Oct 27, 2018 8:42 am

Aside from the over current issues with the PoE HAT. One other annoying characteristic was that the fan would switch on and off as it went above or below the trigger temperature, without any form of hysteresis (despite what the original overlay specified which indicated it should have 5 DegC of hysteresis. Per: viewtopic.php?f=45&t=219050&start=50#p1356682)

Watching the github repository for changes to the fan driver, I noticed a PR was created to implement the missing hysteresis. I've been periodically updating my RPi to see how soon it would make it's way into a release branch and today updating from 4.14.71 to 4.14.78 has added this missing feature.

My Fan now turns on at 50 DegC and off at 45 DegC. No more rapid spinning up and down for the little fan as it hovered around 45 DegC.

The updated kernel isn't yet being pushed out via the normal packaging system, but is available if you run the command:

Code: Select all

sudo rpi-update
Just thought I'd share what I'd found.
Martin

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23059
Joined: Sat Jul 30, 2011 7:41 pm

Re: PoE HAT Fan Hysteresis - Now implemented

Sat Oct 27, 2018 9:06 am

Note that rpi-update brings in bleeding edge kernel and firmware, and is likely less stable that the release version.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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