FSD – Fan Speed Detector

ME 102A Spring 2010April 21, 2010

Jennifer LewStephen Tu

Motivation

Fans provide essential cooling to a computer The fan’s rotational speed is directly related to

its cooling capacity Without properly

calibrated fan, CPUwould almost instantly melt

CPU: http://hardforum.com/showthread.php?t=1423185Fan Grid: http://forums.legitreviews.com/about12716.html

How It Works

Idea: Use fan blades as an Optical Encoder By measuring the number of pulses in a fixed period of

time, can determine speed of blades

Rotary: http://hades.mech.northwestern.edu/index.php/Rotary_EncoderFan: http://computershopper.com/shoptalk/components/silverstone-fm83-cram-more-fan-into-the-same-space

Implementation Plan

1. Fan Voltage Supplied Current Supplied Impellers

2. Sensors Infrared LED Phototransistor Circuit: Resistors, Voltage Supplied

3. LabVIEW VI Input number of impellers Implements GenerateCalibrationCurve() Displays RPM, voltage supplied to fan

4. Error Analysis Sensor is noisy, so must take many samples and

consider confidence intervals

Procedure for calibrating fan

IR LED: http://www.solarbotics.com/assets/images/ir-led/ir-led_pl.jpgPhototransistor: http://farm3.static.flickr.com/2325/2105641666_1487ce594e.jpg

Issues and Scheduling

Issues Current limit on power supply – data at higher voltage values not

truly reflective of fan characteristics▪ Will resolve by using analog lab equipment that does not impose as stringent

current limits.▪ However, this makes the UI less robust, due to less automation

Scheduling Basic prototype implemented last week, but ran into the current issue

above 4/26/2010: Have prototype finished, current issued resolved 4/30/2010: Have prototype tested for robustness, finish error analysis 5/3/2010: Present prototype to customers 5/7/2010: Turn in final report and give final presentation