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Reading Tach Wire Pulses from Fan

Thu Aug 01, 2013 6:38 pm

Hello, I recently purchased a fan to connect to my GPIO. I know everyone says that it isn't necessary, but I mostly want it just get some experience with the GPIO.

The particular fan I purchased has a 3rd wire for the tachometer, I was wondering if it was possible to read the pulses that this wire is sending through the GPIO and get a reading of the fan RPMs.

Also, is is possible to set the GPIO pins to low or high based on a temperature reading from the raspberry pi? Would a CRON job be the best way to accomplish this?

Thanks for the help.

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Re: Reading Tach Wire Pulses from Fan

Wed Aug 07, 2013 4:51 pm

As far as I am concerned, the best way to do fan control is with an off-the-shelf solution.

Here is one that looks easy and is the one I would try first. ... DT7470.pdf

That chip is low cost (about $5) and has many features.

There are other chips available. Google for "I2C fan controller".
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Re: Reading Tach Wire Pulses from Fan

Wed Aug 07, 2013 5:07 pm

This is currently under discussion here: ... 31&t=51501

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