Project

The Electric Chair Sound Machine converts bass frequencies of input audio to vibrate a chair with proportion to the bass. The project demonstrates principles of real-time audio filtering and motor control.

Objectives

• Create a project that can used for demonstrations by ECE ambassadors.
• Get the chair to shake via the motor controlled by bass frequencies.
• Create custom speakers.
• Visually compare original and filtered audio signals

System

Methods

• Music Filtering
  • We used a Raspberry Pi 4B as the main board for processing and display. In addition, we used a Codec HAT as an ADC and DAC to handle input and output.
  • The filtering was designed in MATLAB script and converted to C++. The filtering takes in digitized audio and decimates it to 1 kHz from 8 kHz. The bass frequencies from ~100-400 Hz are extracted and used to control a PWM signal.
• Motor and Driver
  • The motor driver take in 120 V AC from an outlet for power and controls the motor. The PWM is rectified through a simple RC circuit and controls the motor speed. In this way the motor will rotate in proportion to the bass frequency of the music.
  • The motor is mounted to the bottom the chair and an off-center mass is attached to the shaft.
• Speaker
  • We made the speaker from scratch starting with the voice coil from printer paper and using 36 and 30 awg wire. This coil is energized by the ac signal creating an electromagnetic push from the magnet and pull creating sound waves.
  • The speaker receives the music signal after it runs through the codec and an amplifier.

Conclusion

• We were able to control the motor speed with the GPIO on the code.
• We tested the homemade speakers and found them to be of sufficient volume and quality for our project.
• In this project, we learned much about audio processing, as we had little experience with real-time audio processing systems.
• In the future, we would like to make some adjustments to the motor to make a more accurate bass with our motor vibration system.