DJ Controller
A standalone two-deck DJ controller running on the STM32U5, written in Rust.
Author: Stefan Răileanu
GitHub Project Link: link_to_github
Description
A fully standalone two-deck DJ controller built on the STM32U5 microcontroller, written in Rust using the Embassy framework. The board reads WAV audio files from an SD card and performs real-time mixing between two decks.
Each deck has its own jog wheel (a rotary encoder), three EQ knobs (bass, mid, high), a volume knob, and dedicated buttons for Play/Pause, Cue, Loop, Sync, and Headphone Cue Select. One shared TFT display shows track name, position, BPM, and loop state in play mode, or a scrollable file list in browse mode.
Audio leaves the STM32U5 through its internal DAC: the main mix goes via a 3.5mm AUX jack into a Marshall Middleton speaker, and the cued deck is routed through a TPA headphone amplifier to the headphone output.
Motivation
I'm a techno enthusiast and wanted a project that combines the technical skills I'm learning with a hobby I already love.
Architecture
The system is organized around three main components: an Input Handler, an Audio Engine, and a Display Driver.
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Input Handler — reads rotary encoders (jog wheel seek and track browse), potentiometers (EQ bass/mid/high per deck, volume per deck), and buttons (Play/Pause, Cue, Loop, Sync, Headphone Cue).
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Audio Engine — streams two WAV files from SD card over SPI. Each deck runs an independent DSP chain (3-band biquad EQ: low-shelf bass at 200Hz, peaking mid at 1000Hz, high-shelf at 3000Hz), plus loop, cue, sync, and headphone cue routing logic. The internal DAC outputs the main mix on CH1 (Marshall) and the cued deck on CH2 (headphones).
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Display Driver — one ILI9341 2.4" TFT display shows per-deck state. In browse mode: scrollable WAV file list with highlighted selection. In play mode: track name, BPM, progress bar, cue point marker, loop region overlay, and status indicators (SYNC, HP, LOOP, PAUSED).
Log
Week 21 - 27 April
- Completed the documentation and ordered the hardware parts
Week 28 April - 4 May
- Connected all the parts to STM32
Week 5 - 11 May
- Got basic WAV playback working over SPI + DAC
- Added volumes per deck
Week 12 - 18 May
- Implemented dual-deck streaming with ping-pong buffer architecture
- Added 3-band biquad EQ (bass/mid/high) per deck
Week 19 - 25 May
- Implemented browse mode with rotary encoder track selection
- Added Play/Pause, Cue, Loop, Sync buttons
- Added headphone cue routing
- Added display with play mode and browse mode UI
- Finalized hardware connections (design)
Hardware
The controller is built around the STM32U545RE Nucleo board. Two WAV streams are read from a microSD card over SPI. Audio is generated by the STM32U545RE's internal DAC. The main mix goes through a 3.5mm AUX jack into a Marshall Middleton speaker. The cue channel goes through a TPA headphone amplifier to the headphones.
Each deck has a rotary encoder used as jog wheel (seek in track) and browse wheel (select track). Six potentiometers per deck: Bass EQ, Mid EQ, High EQ, and Volume. Five buttons per deck: Play/Pause, Cue, Loop, Sync, Headphone Cue Select. One shared ILI9341 2.4" TFT display (split into two halves, one per deck) connects over SPI1.
Schematics
Bill of Materials
| Device | Usage | Price |
|---|---|---|
| STM32U545RE Nucleo Board | Main microcontroller | — |
| TPA Headphone Amplifier module | Headphone cue output | 24 RON |
| 3.5mm Stereo Audio Jack (female) ×2 | AUX output (Marshall) + headphone output | 4 RON |
| Marshall Middleton | Main speaker via built-in amplifier (AUX in) | — |
| Rotary Encoders ×2 | Jog wheel — seek in track, browse tracks | 10 RON |
| Potentiometers 10kΩ ×8 | EQ Bass/Mid/High ×6, Volume ×2 | 10.48 RON |
| Push Buttons ×10 | Play/Pause ×2, Cue ×2, Loop ×2, Sync ×2, HP Cue ×2 | 8.30 RON |
| ILI9341 2.4" TFT Display ×1 | Track info, BPM, position, browse file list | 34 RON |
| MicroSD card | Storing WAV audio files and BPM metadata | 40 RON |
| Wires, breadboard, capacitors | Wiring and decoupling | 50 RON |
| Total: ~180 RON |
Software
| Library | Description | Usage |
|---|---|---|
| embassy-rs | Async embedded framework for Rust | Main async runtime — drives SPI, DAC, ADC, DMA, GPIO EXTI concurrently |
| embedded-sdmmc | SD card FAT filesystem driver | Reads WAV files and companion BPM .txt files from SD card |
| mipidsi | Display driver (ILI9341/ST7789) | Drives the TFT display over SPI1 |
| embedded-graphics | 2D graphics library | Renders track name, BPM, progress bar, cue/loop markers, browse list |
| libm | Math functions for no_std | Biquad EQ coefficient calculations (sin, cos, pow, sqrt) |