arduino freertos fan rpm video

Posted on Feb 4, 2014

An Arduino measuring the rotational speed of a basic computer fan. It was one of a number of YouTube videos I did as I was studying for a Masters in Computer Science. This particular module was an embedded systems programming course, with a bit of electronics thrown in. Here`s the video: I was recently asked if the schematics were available for this video. Unfortunately

arduino freertos fan rpm video
Click here to download the full size of the above Circuit.

I was unable to locate the schematics as shown in the video, however I do have the source code. This is a simple Arduino Sketch that uses an open source Timer` library. You can download the fan-rpm-sketch source code. When reading this source code please keeping in mind that there are three processes going on: b) IR ISR this interrupt routine is configured to be triggered by the falling edge of the IR input i. e. whenever the leading (or falling, I forget which) fan blade edge passes the sensor c) A Timer routine that is attached to a high speed timer and called every second to calculate the RPM value extrapolated from the number of fins seen that second. The difference between the two is the addition of two modules to the layout the thermistor temperature sensor, and the opto-isolated pulse-width-modulated speed controller. On the software side, we now use FreeRTOS on Arduino. The use of an opto-coupler is separates the low voltage Arduino digital IO from the slightly higher voltage used to power the Arduino board and the Fan. Potentially any voltage is supported up to the limits of the CNY 75B part. The IR transistor from radio shack required a large bias resistance to place it in switching` mode rather than amplification mode. A 100K ohm resistor was chosen. An approximate 100 ohm current limiting resistance for the IR LED was provided through two 47ohm resistors in serial. Using the 12V fan in conjunction with...

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