Bluetooth Pomodoro Speaker
Portable Bluetooth speaker and productivity timer designed from concept through fabrication.
Embedded Systems · Acoustic Design · CAD · Fabrication | May - June 2026
Overview
I designed and built a portable Bluetooth speaker that integrates audio playback with a Pomodoro productivity timer. The system combines an ESP32 microcontroller, I2S digital audio amplification, an OLED timer display, LED mode indicators, rechargeable battery power, and physical controls within a custom wooden enclosure. The Pomodoro timer cycles between 25-minute work sessions and 5-minute breaks, with a 30-minute break after every fourth session. An OLED screen shows the current mode and time remaining, a green or red LED shows whether it's work or break time, and a button resets the timer. The project involved the complete design process from acoustic enclosure modeling and CAD to circuit prototyping, embedded programming, fabrication, assembly, and debugging. Â
Project Details
Solo Project : Design & Fabrication
Tools
SolidWorks · WinISD · Arduino IDE · Fritzer
Hardware
ESP32 · I2S Amplifier · OLED Display · Rechargeable Battery System
Fabrication
CNC Routing · Laser Cutting · Manual Woodworking · Soldering
Skills
CAD · Acoustic Modeling · Embedded Systems · Circuit Integration · Prototyping
Mechanical Design Considerations
Acoustic Volume
The ~4.01 L gross chamber volume carried the acoustic requirements established in WinISD into the physical enclosure design.
Acoustic Simulation
I used WinISD to model the selected Dayton Audio full-range driver and evaluate its behavior in a sealed enclosure. Using the driver's Thiele/Small parameters, I examined how enclosure volume influenced the system's frequency response. This simulation provided a quantitative starting point for the enclosure design.Â
Simulated Frequency Response
WinISD simulation of the sealed loudspeaker system, used to evaluate low-frequency roll-off and the effect of the enclosure on driver response.
Enclosure Design and CAD
Internal Proportions
Unequal 108 × 175 × 212 mm dimensions were used to separate the chamber's principal standing-wave dimensions.
108 × 175 × 212 mm
Dimensioned CAD Drawing
Enclosure Volume
The modeled enclosure volume established the internal-space requirement that was carried forward into the mechanical design of the cabinet.
≈ 4.01 L internal volume
Component Packaging
The enclosure also required space for the ESP32, amplifier, battery/power electronics, OLED, LEDs, controls, and internal wiring without unnecessarily reducing the acoustic chamber volume.
Wire Routing
Cutouts through the internal separators provided paths for the speaker wiring while keeping the acoustic chambers and electronics layout organized.
Electronics & System Integration
The complete electrical system was designed around a shared regulated power supply and common ground, allowing the audio, control, and user-interface subsystems to operate together from the onboard battery system.
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The Arduino IDE code turns an ESP32 into a Bluetooth speaker with a built-in Pomodoro timer. It receives music from a phone over Bluetooth and sends it to a class D amplifier that drives the speaker. At the same time, it controls the Pomodoro timer and displays the mode and remaining time using the OLED display and LED indicators.
Audio System
Bluetooth → ESP32 → I²S → MAX98357A → Drivers
Decoded audio is transmitted digitally to the MAX98357A amplifier using I²S, which drives the full-range speakers.
User Interface
A 128 × 64 OLED displays the timer, while green/red LEDs indicate status. A physical push button resets the sequence.
ESP32-WROVER
Bluetooth + control
MAX98357A
I²S amplification
OLED
Timer interface
LEDs + Button
Physical interface
Battery + Boost
Rechargeable 5 V supply.
Manufacturing & Assembly
My original plan was to laser cut the enclosure panels directly from the CAD geometry. However, during fabrication, the plywood proved too thick for the available laser cutter to reliably cut through. Although the laser could trace the required geometry, it did not fully penetrate the material, requiring me to change the manufacturing approach to CNC machining. Because this occurred near the end of the school year, my remaining access to the shop was limited. I machined as many of the remaining components as possible before losing access to the equipment.
After the school year ended, I brought the unfinished enclosure home to complete the build. At that point, I no longer had access to the laser cutter or CNC router, and my available woodworking equipment was limited to a hand saw. I therefore cut the remaining enclosure pieces manually. The hand-cut components were functional, but they did not achieve the dimensional accuracy or edge quality of the digitally fabricated parts. This is the primary reason the finished enclosure is less visually clean and precise than the Solidworks model.
Prototyping & Testing
During prototyping, I encountered intermittent static and distorted audio caused in part by unreliable breadboard connections and grounding. To improve reliability, I soldered several of the breadboard connections to establish a more secure common ground between the ESP32, amplifier, and power supply. Testing the complete system outside the enclosure kept the electronics accessible and allowed these issues to be identified and resolved before final installation.
Final Prototype & Reflection
The completed prototype successfully integrates Bluetooth audio playback, a functional Pomodoro timer, visual status indicators, and portable battery power within a single custom enclosure. The final system connects wirelessly to a phone or computer for audio playback while independently cycling through work and rest periods on the ESP32. Although manufacturing limitations affected the cosmetic finish of the enclosure, the prototype achieved the project's primary objective: developing a compact, self-contained study speaker while taking the design from acoustic simulation and CAD through electronics, firmware, fabrication, and final system integration.
Final System
Bluetooth Audio
Wireless audio playback through the ESP32 and I²S amplifier.
Custom Enclosure
~4 L sealed acoustic chamber designed through WinISD modeling and SolidWorks CAD.
Future Improvements
A second iteration would focus on improving both manufacturing quality and acoustic performance. I would design the enclosure around a verified manufacturing process from the beginning and complete all precision-critical panel cuts using CNC equipment rather than transitioning between fabrication methods. Acoustically, I would investigate a larger or revised enclosure alignment to reduce the relatively high Qtc = 1.119 and extend the response below the current ~87 Hz F3. I would also improve the internal electronics implementation through cleaner permanent wiring or a custom PCB and perform physical acoustic measurements to compare the completed speaker against the original WinISD predictions.
Pomodoro Timer
25-minute work and 5-minute rest periods with a 30-minute long break after four work cycles.
User Interface
OLED countdown display with dedicated work/rest LED indicators and physical reset control.
Portable Power
Rechargeable battery system with regulated system power and master on/off control.