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Oct 2016 - Dec 2016 

Chordocentric is a music making machine which resembles a rotating Ferris Wheel. The machine consisted of twelve linkage arms which folds up and down to allow the strings to come in contact with the pick, thus producing a sound. Chordocentric consisted of 12 servo motors for each arm, all which are controlled by an arduino microcontroller. The strings connected to each arm could be tuned by tightening or loosening the guitar pegs.  

To create the flipping motion of the arms, a four-bar linkage mechanism, operated by a servo motor was designed. Each arm would be able to move independently of each other and hence, we would be able compose a musical tune. The speed of the rotating disc would control the tempo of the music.

The Ferris Wheel comprised of a front plate, which rotates and plucks the strings and a stationary rear plate, which the arms are secured onto.  

Guitar strings were attached to each end of the arm linkages and are in tension. They were then tuned in a minor pentatonic scale by adjusting the tension of the string with a guitar peg. The frequency of each string depended on its length, tension and mass per unit length. 

The servos were controlled by the Arduino via the digital pins. The 12 servos were powered by a Power Supply Unit (PSU).

To find out the draw current of a single servo, we powered the servo with the +5V pin of the Arduino and measured the current drawn with a multimeter. Each servo drew a current of 0.1A when unloaded and 0.2A when loaded.

Hence, we set the PSU to provide a voltage of 5.0 V and current of 2.4A.

A problem that we had encountered was that the plucked strings did not generate much sound due to the lack of a resonance chamber. To overcome this, we amplified the strings electronically by using piezoelectric transducers.

Vibrations from the strings would create an electrical output. However, the voltage outputs of the piezoelectric transducers were very small. As a result, they needed to be amplified. A LM386, which is a low voltage power amplifier, was used in the design of our amplifier circuit, as shown.

The circuit was powered by a 9V battery. The LM386’s was internally set gain of 200 and tested for the sound output. Each amplifier was used to amplify 4 piezoelectric transducers.  


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