Fake Fan RPM Sensor

[Loz]

Hi, I've read the "Fake Fan RPM Sensor", and it's exactly what I needed, well explained https://www.techidiots.net/notes/fake-fan-sensor

As I don't know that much about electronics (and as I'm lazy), I bought a pre-built module :


I soldered it on a fan plug, and plugged it onto my motherboard. But alas the mobo doesn't see anything.
Does anybody has an idea of what's going wrong ?

I have a multimeter and will be pleased of getting any measure you may need.

[Loz]

Electronic schematic doesn't seem to match...

[ACalcutt]

The fan controller you bought looks a lot more like my schematic than the one you posted. I still am using a few of the ones I made.

Not sure what your issue is, but when I made mine I had to go tripple check the wiring because I made a short where there shouldnt be one. If it is really like the scematic you posted it seems similar, but they are using the 555 pins quite differently.

[ACalcutt]

One thing i would do is check the wiring to the fan. The labeling says its gnd, out, vcc but the plug wiring is gnd (black), vcc (red), out (yellow)

[Loz]

Ok, I checked. The plug is 4pins/pwm, so I soldered black on Ground, green on Out, yellow on VCC, and Blue remains free.

The potentiometer screw has a wide range of resistance, I'm wondering if I a missed an admissible value.

[ACalcutt]

Based on the attached graphic it sounds like you have it right.

FZ6GJXYIKSN2TXA.jpg (65.08 KiB) Viewed 253560 times

For the potentiometer screw, what I did was go into my bios health section and turn the screw the full range until I saw the fan speed I wanted. mainly right now you want to see if you get anything at all by adjusting it, so turn it all the way in one direction, monitor it, and slowly turn it in the other direction and see if anything registers. if it does, tune it based one what you see and want. if you see nothing, that thing could be faulty. do you get anything when a real fan is plugged in?

[Loz]

Yes, I successfully tried several real fans.

Redid all the soldering, checked with multimeter that contacts were ok, and that there I did no shortcut.

I then turned slowly the screw all the way in both directions, but nothing showed up in bios.

It could be a faulty part, yes, but it's frustrating because I don't know I don't know how to check...

[ACalcutt]

So Ground is to Pin1, VCC is to Pin2, and Out is to Pin3 (Pin4, the one farthest from the notch on the fan plug is not connected to anything). Should be right.

A real fan works. Is this like a standard pc fan or something more specialized? what motherboard/server are you trying to use it with?

Basically what this is doing is making a pulse. If you had an osiliscope you could hook up ground and vcc and you should see the pulse on the out pin. that 3rd pin expects 1 pulse every revolution, which this is made to simulate.

From ( https://electronics.stackexchange.com/q ... 0signal%20(tachometer,minute%20times%20with%2060%20seconds.&text=In%20most%20fans%20that%20I,the%20TACH%20or%20tachometer%20wire. )

Brief background: The tachometer output comes from a Hall-effect sensor mounted on the motor driver PCB on the fan frame. One or more magnets embedded in the fan rotor hub activate the Hall-effect sensor as they pass by. The sensor is amplified, and eventually drives a logic circuit. The fans that I have seen use an open drain/open collector output.

One (or more) pulse is generated every time the the fan rotor completes a revolution. The number of pulses counted in one minute is directly proportional to the RPM of the fan..

[Loz]

Thank you!

You gave me the courage to unsold the plug (it was so painful to solder I didn't dare to undo it), and soldered it on another module (I bought 3 of them). It just works!

[ACalcutt]

Glad the other one worked for you

For the soldering comment, these types of projects are why I bought a Crimping Tool for Dupont Pins (like this one https://www.amazon.com/gp/product/B00OMM4YUY ). Which allows you to put on the little ends which would plug right into the header those came with (like https://www.amazon.com/gp/product/B01M3PLNF6 ). then you can just take your fan wire, crimp 3 of the pin ends on, and plug it right into the fake rpm sensor (no soldering involved). Made working with my raspberry pi soooo much easier, since it uses those same type of headers.

[Loz]

The module died.
I put the plug on the third (and last) module I have, without soldering. after connecting, it get burning hot, and prevented the motherboard to boot (I suppose it detected a short-circuit).

[ACalcutt]

Sure sounds like a short. careful, don't break your hardware over a fan (been there before ) .I'd send you a working one if you were interested... sure I could just throw one in an envelope (pm me)

I have a few because my old supermicro had like 8 headers and vmware complained with nothing plugged in, but I've actually started getting 4 pin fans that can use those headers now, so they have been replaced by real fans again.

[Loz]

Oh it so sweet from you, but I live in France, so it's probably not worth the hassle, I'm sure I will find a solution locally. It's just frustrating not to understand what's happening...