Arduino + SI4713

Most users of SI4713 - FM Broadcast Stereo/RDS chipset use Adafruit library.

But there was a problem: instability on initialisation of the chip.
Also, some important functions were missing, like Audio Compression and Audio Limiter.

Therefore, Imodified the library files to resolve the bugs and add those functionalities.

I also added a test .ino file.

Everything is on my GitHub.

Changelog — Adafruit Si4713 Library (local fork)

All changes relative to the original Adafruit Si4713 library (adafruit/Adafruit-Si4713-Library).

---

[1.1.0] — 2026-04-18

Fixed

Adafruit_Si4713.cpp — begin()

• CRITICAL — second root cause of intermittent initialization failures. i2c_dev->begin() (which performs an I2C address scan) was called before reset(). If the chip was in an undefined power-on state it would not ACK its I2C address, begin() returned false, and the MCU required multiple resets before the chip was caught in a good state by chance. Fix: reset() is now called first, giving the chip time to boot before the I2C scan is attempted.

Adafruit_Si4713.cpp — reset()

• CRITICAL — root cause of intermittent initialization failures. After de-asserting NRST (digitalWrite(_rst, HIGH)), the function returned immediately with no delay. powerUp() was then called before the Si4713 had completed its internal boot sequence, causing random I2C command failures on ESP32 and other fast MCUs. Fix: added delay(100) after the final NRST HIGH to satisfy the datasheet power-up timing requirement (Si4712-13-B30-1, §8).

Adafruit_Si4713.cpp — sendCommand()

• The CTS polling loop had no timeout, blocking the MCU indefinitely if the chip failed to assert CTS (e.g. after a failed reset or I2C fault). Fix: added a 5-second timeout; on expiry a diagnostic message is printed to Serial and the function returns gracefully.

Adafruit_Si4713.cpp — getRev()

• Chip revision information (part number, firmware, patch, component, chip rev) was only printed when the SI4713_CMD_DEBUG macro was defined at compile time, making it impossible to verify the detected chip during normal startup. Fix: revision info is now always printed to Serial unconditionally.

• The original debug block printed the firmware word twice (once in the “Part #” line and once in “Firmware”) and never printed the component version (cmp). Both issues are corrected.

• Per the Si4713 datasheet, FWMAJOR, FWMINOR, CMPMAJOR and CMPMINOR are ASCII characters (same encoding as CHIPREV). The previous implementation printed them with Serial.print(..., HEX), producing incorrect output such as Firmware : 32.30 instead of Firmware : 2.0. Fix: all four fields are now displayed with Serial.write().

Adafruit_Si4713.cpp — powerUp()

• Corrected a misleading inline comment: TX_ACOMP_ENABLE = 0x0 was labelled “turn on limiter and AGC” when it actually disables the audio compander. Comment updated to reflect the correct behaviour and documents the alternative values (0x02 = limiter only, 0x03 = limiter + AGC).

Adafruit_Si4713.h — include guard

• Added #pragma once to prevent multiple-inclusion issues when the header is used in a multi-file sketch alongside other Adafruit libraries.

Adafruit_Si4713.h — debug macro name mismatch

• The commented-out debug macro was named SI471X_CMD_DEBUG, while the .cpp implementation checked for SI4713_CMD_DEBUG. Uncommenting the header macro therefore had no effect. Fix: renamed to SI4713_CMD_DEBUG to match the preprocessor guards in the implementation file.

Added

Adafruit_Si4713.cpp / .h — powerDown()

• Implements the POWER_DOWN command (0x11). Puts the chip in low-power state without requiring a hardware reset. Call begin() to restart.

Adafruit_Si4713.cpp / .h — powerUpDigital(sampleRate)

• Alternative to powerUp() for I2S digital audio input (POWER_UP ARG2=0xD0). Configures SI4713_PROP_DIGITAL_INPUT_FORMAT (standard I2S, 16-bit, stereo) and SI4713_PROP_DIGITAL_INPUT_SAMPLE_RATE (default 44100 Hz).

Adafruit_Si4713.cpp / .h — setAudioCompander(mode, threshold, attack, release, gain)

• Convenience wrapper to configure the audio dynamic range compander in one call. Sets TX_ACOMP_THRESHOLD, TX_ATTACK_TIME, TX_RELEASE_TIME, TX_ACOMP_GAIN, then TX_ACOMP_ENABLE (mode last, as required by datasheet). mode: 0=off, 0x02=limiter only, 0x03=limiter+AGC.

Adafruit_Si4713.cpp / .h — setASQThresholds(levelLow, durLow, levelHigh, durHigh)

• Configures Audio Signal Quality thresholds for silence and overdrive detection. Enables both ASQ interrupts (TX_ASQ_INTERRUPT_SOURCE = 0x03) and sets the four threshold/duration properties. Results are readable via readASQ().

Adafruit_Si4713.cpp / .h — scanNoise(startFreq, endFreq, step)

• Scans a range of FM frequencies using TX_TUNE_MEASURE + TX_TUNE_STATUS and returns the frequency (in 10 kHz units) with the lowest noise floor. Default step is 10 (100 kHz channel spacing). Useful for automatic channel selection before transmission.

Adafruit_Si4713.cpp / .h — setRDSpi(pi)

• Standalone setter for the RDS Programme Identifier (PI) code (SI4713_PROP_TX_RDS_PI). Allows changing PI independently of beginRDS().

Adafruit_Si4713.h — ASQ define name aliases

• The original header defined SI4713_PROP_TX_AQS_LEVEL_HIGH and SI4713_PROP_TX_AQS_DURATION_HIGH with a typo (AQS instead of ASQ). Added corrected-name aliases SI4713_PROP_TX_ASQ_LEVEL_HIGH and SI4713_PROP_TX_ASQ_DURATION_HIGH to allow consistent naming in user code.