Audio Frequency Spectrum

Team

Alex Lu, Aman Doshi

Overview

The assembled device listens to ambient sound / music and displays the corresponding frequency spectrum.

Description

The assembled devices uses an electret condenser microphone (CMA-4544PF-W) to listen to ambient sounds. An amplifier circuit amplifies the microphone voltage and links to an ADC pin on an ESP32 controller. The ESP32 uses Fast Fourier Transform to analyze the microphone signal and outputs the frequency on a 2D LED 5x5 matrix.

Features

Power:

Micro USB-B 2.0, provides 5V 1A
5V to 3.3V linear regulator, converts USB-B 5V to 3.3V to power microphone amplifier circuit and ESP32

Microphone:

Electret condenser microphone (CMA-4544PF-W), listens to ambient sounds / music
LM358 operational amplifier, amplify microphone output between 0V and 3.3V

Compute:

ESP32 microcontroller
- 1 ADC channel to convert microphone input into a digital signal
- FFT to analyze the digital signal
- 10 GPIO pins to display frequencies on a 5x5 LED matrix, 1 GPIO pin per row and per column

Test:

4 pin headers (5V, 3.3V, Gnd, microphone output)

Display:

25 LEDs, arranged in a 5x5 grid to display the frequency spectrum of sound
5 Transistors (BC547CTFR) to select LED matrix row via 5 GPIO pins

Schematic

BOM (Bill of Materials)

Front Layout

Back Layout

Full Layout

3D Model

Future Improvements

Test sub-unit functionality prior to sending out the full PCB for manufacturing (e.g., check the LED matrix circuit works on a breadboard)
Use a larger LED display with more columns (e.g., 5 x 12) to display more frequencies
Move components closer together for a more compact PCB design
Build a 3D printed housing for the PCB board
Add a LIPO battery to power the PCB board remotely (no USB connection necessary)
Choose LEDs with different colors for different frequencies (red for low frequencies, blue for middle frequencies, green for high frequencies)
Change the USB Micro-B to USB C

Conclusion

Unfortunately, severe delays by DigiKey led to our components arriving late for the showcase, hence our team was unable to solder any components to our PCB. Still, the HOPE DeCal experience was extremely rewarding. Through the DeCal, we learnt how to use PCB designing software, industrial PCB manufacturing techniques, debugging circuits using oscilloscopes, soldering, ordering components, creating a BOM, and much more!

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