FM Radio — RDA5807M 📻

📋 Overview

A small FM receiver built around the RDA5807M, driven over I2C by either an ESP32-C3 SuperMini or an ESP-12E — the carrier board has a footprint for both and the firmware picks its pin map from whichever core you compile for.

Audio leaves the board on a 2-pin header to a PAM8403 amplifier and a speaker; a telescopic antenna solders to a plated mounting hole. Beyond the original button-cycles-presets behaviour, the current firmware brings up Wi-Fi and serves a web UI at http://radio.local for presets, volume, seek and manual tuning, supports OTA reflashing, and optionally drives an SSD1306/SH1106 OLED.

🔧 Hardware

The board is a 2-layer 47.4 × 28.2 mm carrier. Reference designators differ between the schematic and the PCB silkscreen — both are listed below.

Sch	Silkscreen	Part	Notes
U1	ESP32C3 SuperMini	ESP32-C3 SuperMini	Top side, through-hole module
U2	ESP12E	ESP-12E	Bottom side — the alternate MCU, see below
U3	U3	RDA5807M module (RRD-102/120 style)	I2C 0x10 (sequential) / 0x11 (indexed)
U4	3V3 Reg	AMS1117-3.3, SOT-223	Only needed for the ESP-12E build
C1, C2	C1, C2	Ceramic disc, 5 mm THT	AMS1117 input side
C3, C4	C3, C4	Ceramic disc, 5 mm THT	AMS1117 output side
J2	GND	1×4 header	I2C breakout: SDA, SCL, 3V3, GND — for the OLED
J3	5V	1×2 header	5 V supply in
J4	LO	1×2 header	Audio out: LOUT, ROUT → PAM8403
SW1	RST	1×2 header	Reset, broken out for an external button
SW2	BTN	1×2 header	Preset button, broken out for an external button
H1	H1	M3 mounting hole
H2	H2	M3 plated mounting hole	Carries the ANT net — solder the antenna here

Notes on the BOM:

• The capacitor values are not set in the schematic. C1–C4 are drawn as generic C with 5 mm disc footprints. Fill them in before ordering; the AMS1117 datasheet wants at least 10 µF on the output for stability, which a disc ceramic will not give you.
• SW1/SW2 are drawn as push buttons but laid out as 2-pin headers, so the buttons live off-board. The tactile switches visible on the render are the SuperMini module's own boot/reset buttons, not board parts.
• H3 and H4 exist in the schematic but were never placed on the PCB.
• The PAM8403 amplifier, speaker, Li-Ion cell and TP4056 charger are off-board and not in this project.

📐 Schematic

Click for the full-resolution PDF.

Board

Top	Bottom

The KiCad 9 project is in hardware/. Both custom 3D models (ESP32-C3 supermini v5.step, RDA5807m-RRD-120.step) are committed and referenced through ${KIPRJMOD}, so a fresh clone renders identically:

mkdir -p docs/images

kicad-cli sch export pdf -o docs/images/schematic.pdf "hardware/05_a radio.kicad_sch"
pdftoppm -r 200 -png -singlefile docs/images/schematic.pdf docs/images/schematic

kicad-cli pcb render --side top --quality high --perspective \
  --rotate '-25,0,25' --zoom 0.7 --width 1600 --height 1200 --floor \
  --background opaque -o docs/images/pcb-top.png "hardware/05_a radio.kicad_pcb"

kicad-cli pcb render --side bottom --quality high --perspective \
  --rotate '25,0,25' --zoom 0.52 --width 1600 --height 1200 --floor \
  --background opaque -o docs/images/pcb-bottom.png "hardware/05_a radio.kicad_pcb"

Gerbers are not committed — the exports under hardware/Drill/ predated the current layout, so they are gitignored. Regenerate with kicad-cli pcb export gerbers before ordering.

⚡ Wiring

Signal	ESP32-C3 (U1)	ESP-12E (U2)	Goes to
SDA	GPIO8	GPIO4 (D2)	RDA5807M + J2 (OLED)
SCL	GPIO9	GPIO5 (D1)	RDA5807M + J2 (OLED)
Button	GPIO3	GPIO3 (RXD)	BTN header → GND
Reset	—	RST	RST header → GND

These are the same values the firmware compiles in; the pin map lives in section 2 of the sketch, keyed off ESP8266 / ARDUINO_ARCH_ESP32.

Three things that will bite you

Populate one MCU, not both. The ESP-12E sits on the bottom copper and the SuperMini on the top, so nothing physically stops you fitting both — but they share the I2C bus and the 3V3 rail. Pick one.

Two regulators land on the same 3V3 net. U1's 3.3 pin and the AMS1117's output are the same node. With the SuperMini fitted, its onboard LDO already powers the rail from the 5 V input, so leave 3V3 Reg (U4) and C3/C4 unpopulated. The AMS1117 is only there for the ESP-12E build.

GPIO8 and GPIO9 are ESP32-C3 strapping pins. They are also the I2C bus here. The chip samples both at reset — GPIO9 low selects download mode, and GPIO8 must not be low — so the bus pull-ups have to be strong enough that nothing on the bus drags either line down during boot. If the board only enumerates as a serial port and never runs, this is the first thing to check.

On the ESP-12E, pinMode() on GPIO3 detaches it from UART0 RX: serial output keeps working, serial input does not. That is inherited from the original board and left as-is.

🧠 Design notes

No radio library. The RDA5807M driver is ~180 lines in section 4 of the sketch. The chip is simple enough — 16-bit big-endian registers, two I2C addresses (0x10 auto-incrementing, 0x11 indexed) — that a dependency buys nothing and costs portability across the two cores.

One sketch, two targets, no manual switch. Everything board-specific is behind #if defined(ESP8266) / #elif defined(ARDUINO_ARCH_ESP32): pin map, network headers, the web server type, and the persistence backend (EEPROM on the ESP8266, Preferences on the ESP32). Selecting the board in the IDE is the only choice you make.

The OLED type is a runtime setting, not a compile-time one. SSD1306 and SH1106 are indistinguishable over I2C, so the firmware auto-detects that an OLED is present and lets you switch the controller from the web page. Getting the wrong module in a batch costs a click instead of a reflash. OLED_ENABLED 0 compiles the whole display path out.

Audio survives an OTA update. The RDA5807M only needs the MCU to change station — it keeps playing on its own while flash is being rewritten. Both OTA paths (the Arduino IDE network port and the browser upload at /update) are guarded by OTA_PASSWORD, because otherwise anyone on the LAN can replace the firmware. A failed transfer rolls back to the old image; only a successfully written but broken sketch means opening the box.

Credentials are gitignored. This repo is public, so Wi-Fi and OTA passwords live in secrets.h, which is not tracked. secrets.h.example is the template.

HTTP API

The web page is served from flash at / and drives these endpoints:

Endpoint	Purpose
GET /api/status	Current frequency, volume, stereo/RSSI, preset list
GET /api/preset	Select a preset slot
GET /api/tune	Tune to a frequency
GET /api/volume	Set volume 0–15
GET /api/seek	Hardware seek up/down
GET /api/preset/set	Rewrite a preset slot (persisted)
GET /api/oled	Switch controller: ssd1306 / sh1106 / none
GET/POST /update	Browser firmware upload

🔨 Build

cp Src/test_I2C_Radio/secrets.h.example Src/test_I2C_Radio/secrets.h
$EDITOR Src/test_I2C_Radio/secrets.h

# ESP32-C3 SuperMini
arduino-cli compile --fqbn esp32:esp32:esp32c3 Src/test_I2C_Radio

# ESP-12E
arduino-cli compile --fqbn esp8266:esp8266:nodemcuv2 Src/test_I2C_Radio

Requires the Adafruit SSD1306, Adafruit SH110X, Adafruit GFX and Adafruit BusIO libraries unless you set OLED_ENABLED 0.

Verified with arduino-cli 1.5.1, esp32 core 3.3.8, esp8266 core 3.1.2:

Target	Flash	RAM
ESP32-C3	1,130,767 / 1,310,720 B (86%)	44,252 / 327,680 B (13%)
ESP-12E	340,684 / 1,048,576 B (32%)	31,864 / 80,192 B (39%)

Two figures worth watching: the ESP32-C3 build is at 86% of the default 1.3 MB app partition, and the ESP-12E build sits at 93% of IRAM (61,551 / 65,536 B). Neither has much headroom left for new features.

🚀 First run

1. Copy secrets.h.example → secrets.h and fill in your Wi-Fi credentials and an OTA password.
2. Flash over USB the first time — OTA needs working firmware to update from.
3. Solder a telescopic antenna to the plated mounting hole H2.
4. Wire the LO header to a PAM8403 input and feed 5 V into the 5V header. Take the amplifier's ground from that same header — LO carries only LOUT and ROUT, no ground of its own.
5. Browse to http://radio.local. If mDNS does not resolve, check the serial log for the DHCP address.
6. With no Wi-Fi at all the board still works: the BTN header cycles presets.

📟 Original prototype

The first version of this project was a hand-soldered perfboard build on an ESP-12E with a fixed volume and 10 hard-coded stations — no Wi-Fi, no display, one button. The carrier board above replaces it.

Breadboard wiring	Perfboard build

📜 License

MIT — see LICENSE.