Mark Matamoros ITP Blog

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Fall 2020

Prototyping Electronic Devices

Midterm: Basic Synthesizer with Stretch Band Control Prototype. October 27, 2020.


For my final project, I chose to create a synthesizer with the utilization of an AS3394 (IC), a microcontroller for CV, and a conductive rubber band for dictating the outputted CV level. This work was birthed from my desire to dive in analog synthesizers in conjunction with uncommon controller components.



While I previously utilized the AS3340 (oscillator) and AS3320 (filter) in a prior work, I chose to pick up the AS3394 IC, as it has both oscillator and filter components integrated into one unit. Furthermore, the required voltage is significantly less than the previously mentioned IC's.

Regarding the stretching rubber component (resistor), it is currently being utilized to control the frequency of the oscillator. Within this setup, the rubber band is set up in a voltage dividing manner, where the signal is being sent to an input of the microcontroller. Thereafter, the recieved values are mapped in a manner to be utilized as a control voltage through the utilization of the microcontroller's PWM capabilities.

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It must be noted that the rubber cords are being fastened to a cardboard box within this prototype.

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The following videos display two instances of modulating the oscillator frequency. The first one showcases a simple interaction between an automated sweep of the microcontroller's PWM output. The latter displays the utilization of the rubber resistor in conjunction with the microcontroller and IC.


While the current IC uses a more manageable voltage (-6.5v and 5v) for operation, the control voltages for various aspects of the IC have voltages than range in values that appear to not be typical (EX: -2v to 2v, -2 to 4v, etc.). Due to this situation, I was unable to utilize other aspects of the IC; I blame my inexperience in this type of work. In light of this situation, I am considering a swap of this IC with the previously mentioned AS3340 and AS3320, where the CV's range in the range of 0 to 5v.

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