First version

DigiRadio v1

A 6-layer, 50 × 90 mm board with four main chips, powered over USB-C. It works and I use it every day.

Order it on PCBWay Files on GitHub The v1 firmware

FM / DAB+→Si4684→ I²S →ADAU1701 DSP→ I²S →BT1035→aptX

Si4684

Silicon Labs

DAB+/DAB/FM tuner, external antenna on an SMA connector, its own low-noise 1.8 V rail.

ADAU1701

Analog Devices SigmaDSP

EQ, source mixing, bass and stereo enhancement. It is the I²S clock master (12.288 MHz crystal) and every audio source goes through it.

FSC-BT1035

Feasycom, Qualcomm QCC3056

Bluetooth 5.2 output with aptX, aptX HD and aptX Adaptive.

ESP32-S3

Espressif

Host controller with Wi-Fi and BLE: boots the other chips, streams web radio into the DSP, serves the REST API and handles updates.

Block diagram

FM/DAB antenna → [ Si4684 ] --I²S--> [ ADAU1701 DSP ] --I²S--> [ FSC-BT1035 ] → aptX
                      ↑                     ↑                        ↑
                      └──── SPI ──── [ ESP32-S3 host ] ──── UART ────┘
                                            │  I²C
                                     Wi-Fi · NVS · HTTP API

The board

6 layers, impedance-controlled, two solid ground planes under the RF, crystals and USB.
Three antenna zones: the two 2.4 GHz antennas (ESP32 and BT1035) on opposite corners, FM/DAB on SMA, with keep-outs on every layer.
USB-C, 3.3 V from a buck plus a low-noise 1.8 V LDO for the tuner.
The DSP program is designed in SigmaStudio and can be updated over Wi-Fi without reflashing the ESP32.

Schematic

Tap an image for full resolution. The PDF and KiCad files are on GitHub.

Fabrication

The board was fabricated and assembled by PCBWay, who sponsored part of the cost. With a QFN tuner, an LQFP DSP, two 2.4 GHz modules and a USB-C connector on 6 layers, hand assembly wasn't realistic. The only part they don't stock is the FSC-BT1035, which I soldered by hand.

You can order it from the project page on PCBWay. Disclosure: PCBWay gives me a small percentage of those orders as store credit.

The current version

This board has been superseded by v2: an ADAU1452 DSP instead of the ADAU1701, a BQ25896 charger for battery operation, an FSC-BT1058 Bluetooth module and an optical S/PDIF output.