Accessing The RPM Sensor On A Pc Fan

This one is almost too simple, but it might come in handy. It turns out that Pabst fans (and probably several others) already have the circuitry for RPM monitoring. Pop it apart allow pcb access and add your own RPM sensor lead to the PC board. Not all fans will have it, but it’s a safe bet that it’ll have an RPM sensor instead of a rotor lock indicator on the common PC board component.

21 thoughts on “Accessing The RPM Sensor On A Pc Fan

  1. This is the worst hack I have ever seen on hackaday.
    Honestly, start showing knitting techniques. Most ATX fans already had a 3rd wire. This tutorial was just adding a 3rd wire. WOW! YOU CAN SOLDER 1 WIRE!

    and for the pinout: Googled:”ATX fan pinout”,first thing:

    Shows the pinout of the ATX fan plug that is on every $5 computer fan out there. And yes, IT HAS SENSOR PIN!!!

    If he said how to read the RPM of the fan accurately without a PC, that would be nice.

  2. i have never used a fan with out one already in it (except for in the ps2 and my powersupply) i always buy one wiyh a white or yellow wire on it but i use rpm and cooling sensers alot

  3. Hmm, I have a Microcontollers final project coming up. Using the rpm sensor on the fan and a frequency counter on the chip plus the lcd module I got in a kit reciently could make my own wind speed meter. Add a temp probe and send that out. and you have one of those handheld weather stations.

    This would be killer easy. Pulse counter off the bus clock, a little math to do the conversion, and an output to the lcd screen and I have my project done.

    Thank you hackaday for saving my grade in the class.

  4. I actually just tried doing this the other day with a fan I ripped out of a dead psu. It had only 2 wires, because it didn’t need monitoring in the psu. But, alas it reported 6000 rpm all the time. I might have fried the ic’s while soldering, I suppose.

  5. I have to say, this is actually the exact type of hack that got me into hack-a-day in the first place. It’s all about unleashing the hidden potential of tech, no matter how simple!

  6. from


    [very common]

    1. n. Originally, a quick job that produces what is needed, but not well.

    this is a quick job that gets RPM monitoring from a fan that didnt originally have the connector for that function.

    @ werejag – this is not the same as applying power to an LED. and LED is designed to do that from the moment you buy it, the FAN is not, you have to add the connecter yourself. didnt see you complain about and of the other “add a few wires + connector” hacks

    @ atrain, def, wewjag and bking – got a better hack? submit it or post it in the comments. please don’t just whine about other people’s hacks

  7. Come on guys I know we all love the i built the huge complex stuff outta nothing post but this is a legit hack. Did that fan come with the wire No he added it to unlock an unused feature. Sure it was simple but it worked, and now we know that some of these fans we buy with just 2 wires DO have the solder point for the rpm sense wire. This is a useful hack so stop bitching. Even if your one of those guys that built a cellphone outta radioshack parts you still gotta respect this guy for taking the time to look and figure this out. Lets thing before we flame.

  8. @heter – this is hack is on par with my led comment. the fan came with the rpm sensor built in. if he told how to add rpm sensor or how to read that rpm sensor that would be a hack worth reading.the fan was designed to do that from the moment you buy it. the wiring is a non issue.

    and attacking me because i complain about this is shallow and superficial. i plan to provide a hack soon but its not this add a wire and get on hackaday type.

  9. I was hoping this was a way to grab the RPM’s and use it in our own projects or something.

    Wouldn’t that be handy? Have a relay trigger a powerdown when the RPM’s drop below 1000 or something.

  10. @Heter and shadowslayer: Sing it, brothers!

    @bking: Uh, yeah, well, I work at Initech and I don’t consider myself a pussy, OK?

    @egonis: well, you could do that actually. Just program a PIC or something to count the pulses coming out of the wire. Multiply the number of pulses-per-second by 60 and you’ve got RPM!

  11. @ werejag

    im not attacking you, im just saying that to get this feature on most fans you have to either open them up or cut a bit of plastic away to get to the solder pad, to solder a lead that wasn’ supposed to be on that model of fan

    i do respect your opinion, i just can’t see how this is like wiring up an LED ;)

  12. Hey! I just tried to wire up this LED-thing like you said (“omg we can apply power to these leds and they give light.”). It flashed really bright and then popped & now it won’t light up again -WTF?!?!? That’s a crappy hack if it only works 1x…

    On the other hand, I just today discovered that what I thought was a junk box full of old two-wire fans is actually a junk box half full of old two-wire fans and half full of fans with the potential to be three-wire, rpm monitor fans. That made my day. ;)

  13. Hey, the folks at Hackaday were humorous and good natured enough to post my stupid string tether for the game boy micro hack, and that was a piece of string!!

    They can hang and are open-minded, which is more than I can say for many of you.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.