STM SDR

STM-SDR

A portable FM radio receiver with OLED display, built on STM32F411CEU6 microcontroller with SI4732-A10 software-defined radio chip.

Hardware Components

• Microcontroller: STM32F411CEU6 (96 MHz ARM Cortex-M4, 512KB Flash)
• Radio Receiver: SI4732-A10-GS (FM tuning: 64-108 MHz, I2C interface)
• Display: SH1106 128x64 monochrome OLED (SPI interface)
• User Input: Dual rotary encoders with buttons
• Audio: Stereo audio with RMS monitoring
• Battery: Li-ion monitoring with charging detection
• Power: USB + battery powered

For detailed schematics and PCB design, see the kicad/ folder.

Features

• FM radio tuning with seek functionality
• Real-time audio level monitoring with visual bars
• Battery percentage display
• Configurable settings via menu system:
  • Frequency (64-108 MHz)
  • Volume (0-63)
  • Seek RSSI threshold
  • Mono/Stereo RSSI thresholds
  • Soft mute parameters
  • Antenna selection (internal/external)
• Persistent configuration storage in flash memory
• Dual encoder control for intuitive navigation

Build Instructions

This project uses PlatformIO for build and upload.

1. Install PlatformIO (VS Code extension or CLI)
2. Open the project folder
3. Run platformio run to build
4. Run platformio run --target upload to flash to the board

Requirements

• PlatformIO
• ST-Link debugger for uploading
• GCC ARM toolchain

Usage

Home Screen Controls

• Left Encoder: Rotate to adjust frequency (±0.05 MHz), press to enter menu
• Right Encoder: Rotate to adjust volume (±1), press to toggle mute
• Left Encoder Hold: Seek down
• Right Encoder Hold: Seek up

Menu Navigation

• Left Encoder: Scroll through settings
• Right Encoder: Select setting to adjust value
• Right Encoder Press: Enter/Exit adjustment menu

Settings

1. Tuned Frequency (64-108 MHz)
2. Volume (0-63)
3. Seek RSSI Threshold (0-127 dBuV)
4. Mono RSSI Threshold (0-127 dBuV)
5. Stereo RSSI Threshold (0-127 dBuV)
6. Soft Mute Slope (0-63 dB/dB)
7. Soft Mute Max Attenuation (0-31 dB)
8. Soft Mute Threshold (0-15 dB)
9. Mute (toggle)
10. Mute on Seek (toggle)
11. External Antenna (toggle)

Known Issues/Limitations

• USB D+/D- pins are connected but the USB peripheral is not configured
• Charge controller status line is connected to PA4 but usage commented out (see src/guidraw.cpp)
• OLED dimming and auto-turnoff are not implemented yet
• RDS (Radio Data System) infrastructure missing
• No preset station storage
• Always-on power mode (no sleep)

Future Improvements

• Implement USB peripheral for data transfer
• Use charge controller status monitoring
• Add OLED dimming and auto-turnoff features
• Read and display RDS information
• Add preset station memory
• Add power management with sleep modes

License

This project is licensed under the GNU General Public License v3.0, see the LICENSE file for details.