Tonewheel Synthesizer

We made this project for ME461 Computerized Control of Mechanical Systems at University of Illinois Urbana-Champaign.

Inspired by the Hammond Organ and realized using parts from an electric guitar, this device generates tuned pitches by controlling the speed of a motor with 3 custom tonewheels. Each tonewheel is 3D printed and has the profile of a sine wave along the circumference. Three different wheels are attached to the motor. The wheels have sine waves with 8, 16, and 32 periods to give three different harmonics. The wheels use guitar strings wrapped along the circumference, tied down with copper wire (since copper is not magnetic). Spinning the wheels next to electric guitar pickups induces a signal in the pickups by electromagnetic induction which is sent to a guitar amplifier, producing sound. The three signals generated by each tonewheel are routed through a simple mixer that can be used to adjust the tone similarly to the drawbars on the Hammond.

An OrangePi is used to create a vision system for user input. The frame of the camera is divided visually into 13 sections (corresponding to C to C on a piano). Pointing a laser in view of the camera triggers each note.

Note selection is then sent to the TI MSP430 via I2C. The MSP430 converts the selected note to a target value for a PI control system. The target values are compared against a value generated by the tachometer; these values from the tachometer are scaled and shifted by an op-amp to match the MSP430 ADC input range. Each note is hand tuned by finding the value from the tachometer that corresponds to the frequency of that musical note as we hear it from the amplifier. These values are then hard coded into the MSP430. Motor speed is controlled using PWM and an H-bridge circuit.

Listen to a demo... https://www.youtube.com/watch?v=OStzI0WP2Qc