Hackaday Prize Entry: Open Source FFT Spectrum Analyzer

Every machine has its own way of communicating with its operator. Some send status emails, some illuminate, but most of them vibrate and make noise. If it hums happily, that’s usually a good sign, but if it complains loudly, maintenance is overdue. [Ariel Quezada] wants to make sense of machine vibrations and draw conclusions about their overall mechanical condition from them. With his project, a 3-axis Open Source FFT Spectrum Analyzer he is not only entering the Hackaday Prize 2016 but also the highly contested field of acoustic defect recognition.

open_fft_machineFor the hardware side of the spectrum analyzer, [Ariel] equipped an Arduino Nano with an ADXL335 accelerometer, which is able to pick up vibrations within a frequency range of 0 to 1600 Hz on the X and Y axis. A film container, equipped with a strong magnet for easy installation, serves as an enclosure for the sensor. The firmware [Ariel] wrote is an efficient piece of code that samples the analog signals from the accelerometer in a free running loop at about 5000 Hz. It streams the digitized waveforms to a host computer over the serial port, where they are captured and stored by a Python script for further processing.

From there, another Python script filters the captured waveform, applies a window function, calculates the Fourier transform and plots the spectrum into a graph. With the analyzer up and running, [Ariel] went on testing the device on a large bearing of an arbitrary rotating machine he had access to. A series of tests that involved adding eccentric weights to the rotating shaft shows that the analyzer already makes it possible to discriminate between different grades of imbalance.

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Posture Sensor Reminds You To Sit Up Straight!

Hey you! Are you slouching? Probably. It might not seem like such a bad thing to do, but if you plan on sitting comfortably at that desk for the next 5-10 years or so, you’ve really gotta watch your posture. This is a problem [Max] has been trying to solve for a while now — and now he’s attempting to do it with a posture sensor.

His first take on this project utilized an ultrasound range finder, mounted to the back of a chair. Once calibrated, you would have to maintain a certain distance from the back of your head to the sensor, thus, keeping your back straight. It worked, but it wasn’t the greatest.

Next up, he tried utilizing a webcam and facial recognition software to determine if he was slouching forwards, backwards, or (however unlikely), maintaining good posture. It was better than the first prototype, but still needed some refinement. Now he’s onto his third iteration — this time, a wearable posture sensor!

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