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<div align="center">
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# DigiRadio
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### DAB+/FM Bluetooth Receiver with SigmaDSP Audio Processing
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**Open-source digital radio — Si4684 tuner · ADAU1701 SigmaDSP · Bluetooth aptX Adaptive · ESP32-S3**
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</div>
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---
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## Overview
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**DigiRadio** is an open-source digital radio receiver that combines terrestrial
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broadcast reception (**DAB+ / DAB / FM**) with a programmable audio-processing
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stage and high-quality **Bluetooth** audio output.
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Incoming broadcast audio is decoded by a Silicon Labs **Si4684** digital-radio
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receiver, processed by an Analog Devices **ADAU1701 SigmaDSP** (equalisation,
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mixing, level control), and transmitted over Bluetooth by a Qualcomm QCC3056-based
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**Feasycom FSC-BT1035** module supporting the **aptX Adaptive** codec. An Espressif
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**ESP32-S3** acts as the host controller, orchestrating the three subsystems and
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providing Wi-Fi/BLE connectivity and a USB service interface.
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The entire tuner → DSP → Bluetooth path is **fully digital (I²S, 48 kHz / 24-bit)** —
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no analogue conversions are introduced between the tuner and the wireless link.
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```
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FM/DAB antenna → [ Si4684 ] --I²S--> [ ADAU1701 DSP ] --I²S--> [ FSC-BT1035 ] → aptX
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↑ ↑ ↑
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└──── SPI ──── [ ESP32-S3 host ] ──── UART ────┘
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│ I²C
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```
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---
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## Key Features
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- **DAB+ / DAB / FM** reception (Si4684) via external whip antenna (SMA)
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- **Fully digital audio path** — no avoidable A/D–D/A conversions
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- **Programmable audio processing** on the ADAU1701 SigmaDSP
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- **Bluetooth 5.2** output with **aptX / aptX HD / aptX Adaptive**
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- **ESP32-S3** host with native USB, Wi-Fi and BLE
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- **USB-C powered**; single-rail 3.3 V + low-noise 1.8 V for the tuner
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- **6-layer impedance-controlled PCB**, 50 × 90 mm, two ground planes
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- Three antennas (ESP32 2.4 GHz, BT1035 2.4 GHz, FM/DAB SMA) with proper keep-outs
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---
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## Repository Structure
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```
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DigiRadio/
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├── docs/ Technical Reference Manual (LaTeX source + PDF)
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│ └── DigiRadio_Manual.pdf
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├── Hardware/
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│ ├── schematics/ Schematic (PDF)
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│ ├── gerber/ Gerber + drill files (fabrication)
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│ ├── bom/ Bill of Materials
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│ ├── pick-and-place/ Component placement (CPL / centroid)
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│ ├── easyeda/ EasyEDA source project
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│ └── 3d/ 3D renders / STEP
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└── Software/ Firmware (in development — see Software/README.md)
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```
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---
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## Documentation
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The full design is described in the **[Technical Reference Manual](docs/DigiRadio_Manual.pdf)**,
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covering the system architecture, signal chain, clock and power design, the 6-layer
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stack-up and controlled-impedance strategy, the functional blocks, and the design
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decisions behind the key choices.
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---
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## Design Highlights
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| Topic | Choice | Rationale |
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|---|---|---|
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| **Audio quality** | QCC3056 / aptX Adaptive | The codec is the dominant quality factor on a wireless link; the DAC lives in the sink |
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| **Audio path** | Fully digital I²S | Avoids unnecessary A/D–D/A conversions between tuner and Bluetooth |
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| **I²S master** | ADAU1701 (12.288 MHz) | Clean ×256 → 48 kHz; avoids sample-rate mismatch |
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| **Stack-up** | 6-layer, 2× GND | Solid ground reference under RF, crystals and USB |
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| **USB routing** | TOP, ref. GND | 90 Ω diff achievable at manufacturable geometry |
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| **Antennas** | 3 zones, diagonal 2.4 GHz | Coexistence separation + full-layer keep-outs |
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---
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## Status
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- ✅ **Schematic** — complete and reviewed
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- ✅ **PCB layout** — 6-layer, DRC clean, plane continuity verified
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- ✅ **BOM** — finalised (manufacturable / sourced)
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- 🔜 **Prototype** — in fabrication (PCBWay)
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- 🛠️ **Firmware** — in active development (released after bring-up)
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---
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## Manufacturing
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The board is manufactured with **PCBWay** as a 6-layer, impedance-controlled PCB
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with turnkey assembly. The FSC-BT1035 Bluetooth module is sourced from Feasycom
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(the footprint uses a BT806-compatible, pin-identical land pattern). See the
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[Manufacturing chapter](docs/DigiRadio_Manual.pdf) of the manual for fabrication
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notes, impedance-control settings and MSL-3 handling of the BT module.
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---
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## License
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- **Hardware** (schematic, PCB, Gerber): [CERN-OHL-S](https://ohwr.org/cern_ohl_s_v2.txt)
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- **Firmware / software**: [MIT](https://opensource.org/licenses/MIT)
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- **Documentation**: CC BY 4.0
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Intellectual property of the design remains with the author. You are free to study,
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modify and build the hardware under the terms of the respective licenses.
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---
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## Author
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**Michele Bigi** — Open-source hardware project.
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*Contributions, issues and questions are welcome via the repository issue tracker.*
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