Radio 04/12/2025

SI4732 Radio

Building a Compact Shortwave Radio with the SI4732 and ESP32-S2 Mini

I recently completed a DIY radio project using the SI4732 receiver module paired with an ESP32-S2 Mini, and I wanted to share a quick walkthrough of the build process. The goal was to create a compact, fully-featured HF receiver that could tune through the shortwave bands with a sleek interface.

๐Ÿง  Core Components

Here’s what went into the build:

  • ESP32-S2 Mini: Handles all the logic and display control. I chose the S2 variant for its USB support and lower power consumption.
  • SI4732 Module: This is the heart of the radio. The SI4732 covers a wide range of frequencies (AM/FM/SW/LW) and provides digital tuning with great performance.
  • 360-Degree Rotary Encoder: Used for frequency tuning. Pressing the encoder also handles mode switching.
  • Sharp LS027B7DH01 LCD: A beautiful 2.7″ memory-in-pixel display (400×240) that offers excellent contrast and low power usage โ€” perfect for portable radio use.

๐Ÿ”ง Inside the Box

The internals are housed in a 3D-printed enclosure. The ESP32-S2 is wired to a small perfboard with logic-level interfacing to the SI4732 and the rotary encoder. I also included level shifting and filtering as needed, given the LCD and radio moduleโ€™s voltage requirements.

The wiring may look a bit wild, but it’s all neatly soldered and tested โ€” each twisted pair minimizes noise and crosstalk, which is especially important when working with RF and display signals in close proximity.


๐Ÿ“ป The User Interface

The front of the device features the LS027B7DH01 LCD. The display shows real-time frequency, modulation mode, signal strength, SNR, bandwidth, and more. There’s also a spectrum waterfall to visualize signal activity.

  • Tuning is smooth thanks to the rotary encoder.
  • Pressing the encoder switches modulation (USB, LSB, AM, FM).
  • Band info and S-meter readings are clear even in daylight, thanks to the Sharp displayโ€™s excellent readability.

๐Ÿ’พ Source Code

You can find the full source code and documentation for this project on GitHub:

๐Ÿ‘‰ https://github.com/joaquimorg/si4732-radio

๐Ÿ‘‰ Schematics

๐Ÿ‘‰ 3D Case



๐Ÿ“ก Listening to FT8 Ham Radio

One of the coolest applications of this receiver is decoding FT8, a popular digital mode used by amateur radio operators for weak-signal communication. Despite using just a simple wire antenna, I was able to receive signals from all over the world.

By routing the audio output from the radio into my computer running WSJT-X or JTDX, I can decode FT8 transmissions and visualize them in real time. Here’s a screenshot from a recent session:

Each yellow pin on the map represents a station I received โ€” from Europe and the Middle East all the way to Indonesia. The call roster in the window shows real-time signal reports and distances.

This setup turns the radio into a powerful tool for HF band exploration, propagation monitoring, and DX chasing, all with compact hardware and minimal power consumption.