Car Tachometer Gauge to PC fan

Nicole Drayton · Feb 12, 2016

Hi Guys,

Need some help to wire a Car Tachometer :-http://www.ebay.co.uk/itm/Tachometer-Gauge-Kit-Blue-LED-11000RPM-12V-Meter-Shift-Light-Indicator-4G4F-/111760624565?hash=item1a0573cbb5:g:tosAAOSwgQ9V5Yks

To work in a PC mod im doing, would like it to read the RPM from cpu fan. I got the Gauge to turn on with 12v from molex connector, but how do i read the rpm from fan so the needle reacts on gauge?

P4-630 · Feb 12, 2016

I don't think it will work...

RCoon · Feb 12, 2016

Figure out which pins provide power to the fan, and which single pin shows the speeds. I see four pins in all, so I'm guessing one is PWM control. Basically Red + Black cables are power and ground, and then green and blue are either Tachy + PWM or PWM + Tachy. You'll have to figure out which one is which. Some fans label the last two with different colours depending on manufacturer.

sneekypeet · Feb 12, 2016

Third wire is rpm on a fan.

Ferrum Master · Feb 12, 2016

11 000 RPM Fan? wut?

MIRTAZAPINE · Feb 12, 2016

Ferrum Master said:
11 000 RPM Fan? wut?

Yes this. Pc fans rpm would be around 1000 to 2000 rpm for normal fans. The fastest pc fan is the 7200 rpm delta. and they are vacuum loud. Like the other said use the the tachy wire usually the blue one from the motherboard. It is also called rpm sense. The other wire is a pwm signal. The remaining red and black is the positive and negative terminal of the fan.

silentbogo · Feb 12, 2016

The idea is cool, but you will need some additional electronics to make it work. It is not a simple plug-and-play.
1) There are tachometers that either use pulses, or analog signal to measure RPM. You need to know exactly which interface this device has. There are also aftermarket signal converters, but those will make your project more expensive.
2) In either case, tach needs more current on the signal line, than what a fan signal can effectively provide (especially if you are planning on splitting the fan connector for MoBo and Tach). You must drive the signal through some kind of amplifier and think about electrical isolation, so you won't accidentally fry something.
3) Scaling. YOu won't have an 11K RPM fan in your PC, so if you want a purely cosmetic fan indicator, then you'll have to figure out the way to scale the signal for your particular fan (easy to do with analog signal, but not so with PWM)

There will be lots of other stuff to consider, but at least you can start from this.

RCoon · Feb 12, 2016

Ferrum Master said:
11 000 RPM Fan? wut?

Never seen a Nidec UltraFlo in action? I have four custom cabled ones in my man-draw. Never used them for anything besides cooling my face on a hot day. They were rescued from factory machines.

Ferrum Master · Feb 12, 2016

RCoon said:
Never seen a Nidec UltraFlo in action? I have four custom cabled ones in my man-draw. Never used them for anything besides cooling my face on a hot day. They were rescued from factory machines.

Still he needs a frequency multiplier + driver and then to this device... Not worth by any means...

The logical solution is the tear down the device and drive it using one Atmel Attiny sensing on capture pin in the PWM and driving the needle on output pin...

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Car Tachometer Gauge to PC fan

Nicole Drayton

New Member

P4-630

RCoon

sneekypeet

Retired Super Moderator

Ferrum Master

MIRTAZAPINE

silentbogo

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RCoon

Ferrum Master

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