# Fan RPM-Signal readout

**URL:** <https://discourse.nodered.org/t/fan-rpm-signal-readout/3525>\
**Category:** General\
**Created:** [28 September 2018 11:57 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525 "2018-09-28T11:57:49Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![chkdsk](https://avatars.discourse-cdn.com/v4/letter/c/90ced4/32.png) [@chkdsk](https://discourse.nodered.org/u/chkdsk)\
**Post date:** [28 September 2018 11:57 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/1 "2018-09-28T11:57:49Z")

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Hey everyone!

As I off-topicly mentioned in Gummix' thread ([Temperature controlled PWM Fan](https://discourse.nodered.org/t/temperature-controlled-pwm-fan/2567)), I'm desperately trying to get a readout of a fan's RPM-Signal. Everything I got from the rpi-GPIO-Node could not be interpreted in any way to make sense - at least not to me. I'm not even sure if the processing of the readout in Node-RED is fast enough to accomplish that, the Rasperry Pi 3 should be. Has anyone faced this topic? Any hints?

By the way... I'm using the Arctic F14 PWM fan.

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**Author:** ![Balouzard](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/balouzard/32/2869_2.png) [@Balouzard](https://discourse.nodered.org/u/Balouzard)\
**Post date:** [28 September 2018 12:23 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/2 "2018-09-28T12:23:59Z")

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Hi there,  
Can you please provide us with a sample of data that you get from your fan ?  
Btw, correct me if I'm wrong but I'm not so sure your fan is "sending" proper data to read in the first place 🤔  
If I remember correctly you have to read the fan's signal duty cycle to get a percentage over maximum potetial usage...

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**Author:** ![Gummix](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/gummix/32/10828_2.png) [@Gummix](https://discourse.nodered.org/u/Gummix)\
**Post date:** [28 September 2018 12:41 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/3 "2018-09-28T12:41:21Z")

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Maybe use a Arduino with Firmdata connected to a Raspberry?

> **[Reading DC Fan RPM With Arduino](https://www.instructables.com/id/Reading-DC-Fan-RPM-With-Arduino/)**
>
> Reading DC Fan RPM With Arduino: Source: http://www.theorycircuit.com/reading-dc-fan-rpm-arduino/Reading DC Fan RPM (Revolutions per minute or Rotation per minute) is very easy than we think, yes because DC fan internally contains Hall Effect sensor,...

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**Author:** ![chkdsk](https://avatars.discourse-cdn.com/v4/letter/c/90ced4/32.png) [@chkdsk](https://discourse.nodered.org/u/chkdsk)\
**Post date:** [28 September 2018 15:02 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/4 "2018-09-28T15:02:29Z")

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> [@Balouzard](#):
>
> If I remember correctly you have to read the fan's signal duty cycle to get a percentage over maximum potetial usage

Well, that sounds familiar. I drop some data here as soon I'm back home, tomorrow. With the duty-cycle method it worked on the Arduino, already, but it doesn't after transferring this idea to Raspberry with Node-RED. Probably, because I do it wrong. The stuff I read about these signals is often pretty conflicting. Some say you have to evaluate the duty cycle, some say it's just a hall-sensor and you have to count the peaks per minute (the last thing seems not right to me, now).

> [@Gummix](#):
>
> Maybe use a Arduino with Firmdata connected to a Raspberry?

Yeah,but that would be my third-best solution, if I can't work this out with the help of the forum. My second idea is to read it out on another level outside of node red and pass this to the software. But first things first 😉

I really can't believe, that this is due to the limitations of the Raspi-Hardware, after reading this:  
[http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/](http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/)  
Okay, he only tested the output, but...

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**Author:** ![Balouzard](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/balouzard/32/2869_2.png) [@Balouzard](https://discourse.nodered.org/u/Balouzard)\
**Post date:** [28 September 2018 19:35 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/5 "2018-09-28T19:35:01Z")

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![Sans%20titre](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/2X/c/c67a885f17f11a9d2ea13be39838e964c11bc624.png)  
Sorry for this sketchy... sketch 😄 But I opened some old electronic course and this is duty cycle @chkdsk

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**Author:** ![Gummix](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/gummix/32/10828_2.png) [@Gummix](https://discourse.nodered.org/u/Gummix)\
**Post date:** [29 September 2018 01:07 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/6 "2018-09-29T01:07:35Z")

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> **[12 Volt Lüfter per externe Spannung versorgen per PWM steuern und Drehzahl...](https://forum-raspberrypi.de/forum/thread/5192-12-volt-luefter-per-externe-spannung-versorgen-per-pwm-steuern-und-drehzahl-ausl/)**
>
> Hallo,
> 
> ich habe einen 4 PIN PWM-Lüfter http://www.elektronik-kompendium.de/sites/com/1503111.htmIch hatte mir jetzt gedacht ich gebe auf PIN 1 und 2 des Lüfters 12 Volt aus einem anderen Netzteil. Gleichzeitig verbinde ich den PI mit PIN 1 und 4 um…

  
😉

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**Author:** ![chkdsk](https://avatars.discourse-cdn.com/v4/letter/c/90ced4/32.png) [@chkdsk](https://discourse.nodered.org/u/chkdsk)\
**Post date:** [29 September 2018 19:36 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/7 "2018-09-29T19:36:16Z")

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That link is great! I told you about the annoying noise. It's gone since I generate the signal using the exec node to set up the pwm frequency and generate the pwm signal.

Since my vacation is over now, I need to find the time to handle the rest, but I keep going!

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**Author:** ![TeWe](https://avatars.discourse-cdn.com/v4/letter/t/ecccb3/32.png) [@TeWe](https://discourse.nodered.org/u/TeWe)\
**Post date:** [19 March 2021 18:14 UTC](https://discourse.nodered.org/t/fan-rpm-signal-readout/3525/8 "2021-03-19T18:14:46Z")

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Hello,  
did you find a solution for reading out the pwm signal? I'm trying to read out a pump that generates a 75Hz pwm signal with node red and would appreciate your help.  
Thanks a lot in advance!  
best regards