ESP32-C3 FM Radio Clock Build

Parts List

Everything shares one I2C bus, so the wiring stays simple regardless of how many modules you add.

ESP32-C3 Super Mini Pinout

Pins actually used in this build are highlighted in green. Pins to avoid are marked amber.

Complete Pin Map

Final, verified pin assignments after full build and debug.

Power & I2C bus (shared by all three modules)

Buttons

Pins to avoid on this board

Wiring Diagram

Schematic view — all three I2C peripherals branch off the same SDA/SCL pair.

Project Setup

1. Install PlatformIO in VS Code

   Install the PlatformIO IDE extension, then create a new project targeting board esp32-c3-devkitm-1, framework Arduino.

2. Set up platformio.ini

   Set upload speed to 115200 for reliability, and add the four required libraries (see below).

3. Place firmware in src/main.cpp

   Only one entry-point file may exist in src/. Remove any leftover .ino or backup .cpp files — duplicate globals cause linker errors.

4. Wire the hardware per the pin map above

   Double-check GND is common across every module and button before powering on.

5. Build and upload

   Use the PlatformIO toolbar icons (checkmark = build, arrow = upload) rather than a plain terminal, since pio often isn't on Windows' PATH by default.

platformio.ini

; ESP32-C3 Super Mini — FM Radio + Digital Clock

[env:esp32-c3-devkitm-1]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino

upload_speed = 115200
monitor_speed = 115200

lib_deps =
    https://github.com/pu2clr/RDA5807.git
    adafruit/RTClib@^2.1.4
    adafruit/Adafruit SSD1306@^2.5.13
    adafruit/Adafruit GFX Library@^1.11.11
    adafruit/Adafruit BusIO@^1.16.1

Firmware Flow

How the sketch moves from boot through the button/screen state machine.

Debounce logic (the part worth getting right)

Each button tracks two separate values: a raw reading (updates instantly every loop) and a confirmed stable reading (only updates once the raw value has held steady for 40ms). The action fires only when the stable value changes — this is what prevents one physical press from registering as multiple rapid actions.

Preset Stations

UP/DOWN jump directly between these instead of stepping 0.1MHz at a time.

Edit presetFreqs[] and presetNames[] together (same order, same length) to change the list. Frequencies are in units of 10kHz — 90.5 MHz is written as 9050.

Speaker Output

Swapping the 3.5mm earpiece for a real speaker needs an amplifier stage in between — the RDA5807M's output is line-level, not enough to drive a speaker cone directly.

Add a class-D amp module

A PAM8403 breakout is the standard hobbyist choice — cheap, stereo, and simple to wire.

Finding L/R on the RDA5807M module

Budget RDA5807M breakouts route audio straight to an onboard 3.5mm jack rather than breaking L/R out to the header pins — so there's nothing labeled "L" or "R" to find on the pin header itself. You have two ways to tap into it:

Confirming before committing wire

1. Test with real headphones first

   Confirm you get sound through the jack at all before modifying anything.

2. Map the pads with a multimeter

   Insert a spare 3.5mm plug, set the meter to continuity mode, and probe each PCB solder tab against the plug's tip/ring/sleeve to confirm which pad is which — exact layouts vary between manufacturers even for the "same" module.

3. Wire to the amp

   Tip → L_IN, Ring → R_IN, Sleeve → GND on the PAM8403.

Practical notes

Lessons Learned

Real issues hit during this build, and what actually fixed them — worth reading before your next build to skip the detour.

Build Checklist