The Marimbatron is [Leo Kuipers] ‘s final project as part of the MIT “Fabacademy program” supervised by [Prof. Neil Gershenfeld] of the Center for Bits and Atoms. The course aims to learn how to leverage all the fab lab skills to create unique prototypes using the materials at hand.
The final polyurethane/PET/Flex PCB stack-up for the sensor pad
Fortunately, one of the main topics covered in the course is documentation, and [Leo] has provided ample material for review. The marimba consists of a horizontal series of wooden bars, each mounted over a metal resonator tube. It is played similarly to the xylophone, with a piano-type note arrangement, covering about five octaves but with a lower range than the xylophone. [Leo] converted this piano-type layout into a more logical grid arrangement. The individual pads are 3D printed in PETG and attached to a DIY piezoresistive pressure sensor made from a graphite-sprayed PET sheet laid upon a DIY flexible PCB. A central addressable LED was also included for indication purposes. The base layer is made of cast polyurethane, formed inside a 3D-printed rigid mould. This absorbs impact and prevents crosstalk to nearby sensors. The sensor PCB was initially prototyped by adhering a layer of copper tape to a layer of Kapton tape and cutting it out using a desktop vinyl cutter. While this method worked for the proof of concept, [Leo] ultimately outsourced the final version to a PCB manufacturer. The description of prototyping the sensor and dealing with over-moulding was particularly fascinating.
For the electronics, a modular approach was needed. Each row of ten sensors was daisy-chained to connect the LEDs, with an individual sense line passed down for each s ..
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