June 23, 2013
June 23, 2013
June 26, 2013
Division Experimentation & Lab-Oriented Studies
23.265.1 - 23.265.14
Mobile Experiment for Signals and Systems Analysis of a Guitar String (Bring-Your-Own-Experiment Submission)Students in lecture-based courses would benefit greatly from the addition of mobile hands-onlabs, that is, labs that can be done anywhere anytime such as in the classroom or at home.Recent advances in low-cost portable data acquisition boards, such as a myDAQ, facilitate thistype of pedagogy that more carefully integrates theory taught traditional classes withexperiments done traditionally in dedicated labs. Signals and systems courses are consideredto be very abstract and mathematical by many students, and consequently, very difficult tounderstand. A vibratory experiment that uses multiple senses, such as sight and sound, inaddition to the analysis of measured data can help many students understand this topic better.The experimental platform consists of a guitar string mounted on a portable platform with aguitar pick-up acting as the transducer. The experiment is used in a lecture-based signals andsystems class as an in-class experiment to be done by students at their desks working in two-person groups. The lab consists of a prelab where they compute the transfer function of thestring and plot the frequency response. During lab, they use a screw driver shaft to impart animpulse to the system and they also pluck the string to see the free response. They are askedto adjust system properties such as the tension in the string and the length of the string (byusing a fret). A RockIt™ speaker is used as a small, cheap vibration shaker to excite the systemsinusoidally and to do a sine sweep.The fundamental concepts explored in the experiment are harmonic content of signals, impulseresponse, initial condition response, calculating a transfer function from equations, calculatingand plotting the frequency response from the model, frequency response from impulseresponse data and from sine sweeps, resonance and low damping in systems, and frequencyresponse dependence on physical properties of the system.
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