SI4735 SI4732 all band radio receiver LW MW FM SW

Circuit diagram SI4735 SI4732 DSP all-band radio LW AM FM SW SSB arduino mini

Circuit Arduino + SI4735 or SI4732 all band radio receiver LW, MW, FM, SW and SSB. All-band radio receiver project, using the Silicon Labs SI4735-D60 or SI4732-A10 integrated circuits, with the PU2CLR SI4735 Library for Arduino. An excellent work by Ricardo Lima Caratti (PU2CLR), can be used, Arduino, ATTINY85, ESP32, ESP8266, STM32 or others. Several displays can be used.

Complete circuit for you to assemble a DSP compatible radio receiver to receive LW (Long Wave or low frequency wave) from 153 to 279 KHz, AM or MW (Medium Wave) from 520 to 1710 kHz, SW (Short Wave or metric decay wave) Tropical Wave Radio (2.3 MHz – 5 MHz), Short Wave Radio (5.9-26.1 MHz) and FM Radio (64-108 MHz). Plus patch for SSB and USB.

About SI4735
The Si4735 is the industry’s first fully integrated, 100% CMOS AM/FM/SW/LW radio receiver IC. Offering unmatched integration and PCB space savings, the Si4734/35 requires minimal external components and less than 20 mm2 of board area, excluding the antenna inputs. The Si4735 AM/FM/SW/LW radio provides the space savings and low-power consumption necessary for portable devices while delivering the high performance and design simplicity desired for all AM/FM/SW/LW solutions. Leveraging Silicon Laboratories’ proven and patented Si4700/01 FM tuner’s digital low intermediate frequency (low-IF) receiver architecture, the Si4735 delivers superior RF performance and interference rejection in AM, FM, and short wave and long wave bands. The high integration and complete system production test simplifies design-in, increases system quality, and improves manufacturability.

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Si4735 Block Diagram Si4735 Pinout Datasheet
Si4735 Block Diagram Si4735 Pinout Datasheet

The Si47335 is a feature-rich solution including advanced seek algorithms, soft mute, auto-calibrated digital tuning, and FM stereo processing. In addition, the Si4735 provides analog or digital audio output and a programmable reference clock. The device supports I2Ccompatible 2-wire control interface, SPI, and a Si4700/01 backwards-compatible 3-wire control interface. The Si4735 utilizes digital processing to achieve high fidelity, optimal performance, and design flexibility. The chip provides excellent pilot rejection, selectivity, and unmatched audio performance, and offers both the manufacturer and the end-user extensive programmability and flexibility in the listening experience. The Si4735 incorporates a digital processor for the European Radio Data System (RDS) and the North American Radio Broadcast Data System (RBDS), including all required symbol decoding, block synchronization, error detection, and error correction functions. Using RDS, the Si4735 enables broadcast data such as station identification and song name to be displayed to the user.


  • Worldwide FM band support (64–108 MHz)
  • Worldwide AM band support(520–1710 kHz)
  • SW band support (2.3–21.85 MHz)
  • LW band support (153–279 KHz)
  • Excellent real-world performance
  • Freq synthesizer with integrated VCO
  • Automatic frequency control (AFC)
  • Automatic gain control (AGC)
  • Integrated LDO regulator
  • Digital FM stereo decoder
  • Programmable de-emphasis
  • Adaptive noise suppression
  • AM/FM/SW/LW digital tuning
  • No manual alignment necessary
  • Adjustable channel filters
  • EN55020 complaint
  • Programmable reference clock
  • Digital volume control
  • Adjustable soft mute control
  • RDS/RBDS processor (Si4735 only)
  • Optional digital audio out (Si4735 only)
  • 2-wire and 3-wire control interface
  • 2.7 to 5.5 V supply voltage
  • Wide range of ferrite loop sticks and air loop antennas supported
  • 3 x 3 x 0.55 mm 20-pin QFN package
  • Pb-free/RoHS compliant


  • Table and portable radios
  • Stereos
  •  Mini/micro systems
  •  Portable media players
  • Boomboxes
  •  Clock radios
  •  Modules
  • Entertainment systems
  • Cellular handsets

About Si4732-A10
The Si4732-A10 digital CMOS AM/FM/SW/LW/RDS radio receiver IC integrates the complete broadcast tuner and receiver function from antenna input to digital audio output. The device leverages the Silicon Labs broadcast proven digital low-IF architecture, enabling a cost-effective digital audio platform for consumer electronic applications with high TDMA noise immunity, superior radio performance, and high fidelity audio power amplification. Offering unmatched integration and PCB space savings, the Si4732-A10 requires only a few external components and less than 15 mm2 of board area, excluding the antenna inputs. The Si4732-A10 AM/FM/SW/LW/RDS radio provides the space savings and low power consumption necessary for portable devices while delivering the high performance and design simplicity desired for all AM/FM/ SW/LW/RDS solutions.

Si4732 Block Diagram Si4732 Pinout Datasheet
Si4732 Block Diagram Si4732 Pinout Datasheet


  •  Worldwide FM band support (64–108 MHz)
  • Worldwide AM band support (520–1710 kHz)
  • SW band support (2.3–26.1 MHz)
  •  LW band support (153–279 kHz)
  • Excellent real-world performance with integrated AM/FM/SW/LW/RDS
  • Integrated VCO
  • Advanced AM/FM seek tuning
  • Automatic frequency control (AFC)
  • Automatic gain control (AGC)
  • Digital FM stereo decoder
  • Programmable de-emphasis
  • Advanced Audio Processing
  • Seven selectable AM channel filters
  • AM/FM/SW/LW digital tuning
  • EN55020 compliant
  • No manual alignment necessary
  • Programmable reference clock
  • Adjustable soft mute control
  • RDS/RBDS processor
  • Digital audio out
  • 2-wire and 3-wire control interface
  • Integrated LDO regulator
  • Wide range of ferrite loop sticks and air loop antennassupported
  • SOIC package
  • RoHS compliant


  • Table and portable radios
  • Mini/micro systems
  • CD/DVD and Blu-ray players
  • Stereo boom boxes
  • Modules for consumer electronics
  • Clock radios
  • Mini HiFi and docking stations
  • Entertainment systems

One of the projects using this IC and seen being discussed in forums was The Elektor DSP radio.

Silicon Labs provides extensive PDF documentation on these ICs as well as documentation on programming and application notes for use with evaluation boards.

Part NumberDescriptionFM TransmitterFM ReceiverAM ReceiverSW/LW ReceiverWB ReceiverRDSHigh Performance RDSRPSSAMEDigital InputDigital OutputEmbedded FM antennaAEC-Q100 QualifiedPackage Size (mm)
Si4700FM ReceiverX4×4
SÍ4701FM Receiver with RDSXX4×4
Si4702FM ReceiverX3×3
Si4703FM Receiver with RDSXX3×3
Si4704FM ReceiverXX3×3
Si4705FM Receiver with RDSXX2XX3×3
Si4706 1High Performance RDS ReceiverXXXXX3×3
Si4707 1WB Receiver with SAMEXX3×3
Si4708FM ReceiverX2.5×2.5
Si4709FM Receiver with RDSXX2.5×2.5
SÍ4710FM TransmitterXXX3×3
Si4711FM Transmitter with RDSXXXX3×3
SÍ4712FM Transmitter with RPSXXXX3×3
SÍ4713FM Transmitter with RDS & RPSXXXXX3×3
Si4720FM TransceiverXXXXX3×3
Si4721FM Transceiver with RDSXXXXXXX3×3
Si4730AM/FM ReceiverXX3×3
Si4731AM/FM Receiver with RDSXXX2X3×3
Si4734AM/SW/LW/FM ReceiverXXX3×3
Si4735AM/SW/LW/FM Receiver with RDSXXXX2X3×3
Si4736AM/FM/WB ReceiverXXX3×3
Si4737AM/FM/WB Receiver with RDSXXXXX3×3
Si4738FM/WB ReceiverXX3×3
Si4739FM/WB Receiver with RDSXXXX3×3
Si47401AM/FM ReceiverXXX4×4
Si47411AM/FM Receiver with RDSXXXXXX4×4
Si47421AM/LW/SW/FM/WB ReceiverXXXXX4×4
1. Si4706, Si4707, and Si474x are covered under NDA.
2. High Performance RDS is available in SÍ4705/31/35/85-D50 and later.
2. High Performance RDS is available in SÍ4705/31/35/85-D50 and later.

Ricardo Caratti (PU2CLR) provides the PU2CLR SI4735 Library for Arduino with extensive documentation and usage examples in Portuguese and English, as well as several videos explaining the implementation and use of the circuits. You can also join groups on Facebook to exchange information and Ricardo himself is available to answer questions. The groups are Si47XX for radio experimenters and Si47XX para radioescutas, the latter in Portuguese.

Circuit diagram SI4735 SI4732 DSP all-band radio LW AM FM SW SSB

Circuit Diagram Si4735 Si4732 Dsp All-Band Radio Lw Am Fm Sw Ssb
Circuit Diagram Si4735 Si4732 Dsp All-Band Radio Lw Am Fm Sw Ssb

I chose to use the Arduino mini PRO 3.3V, for having some units available, was used the power supply of the Arduino to power the OLED Display 128×64. The power supply of the board can be by rechargeable battery or USB cable by 5V source with good filtering, should not exceed 5V. The mosfet Q2, when connected voltage to the USB connector disconnects the battery supply, this circuit is optional.

Battery Charger
For charging the battery the TP4056 or TC4056 IC was used, being a complete one for charging a Li-Ion battery as a linear charger of constant current and constant voltage. LED1 shows that the battery is being charged and LED3 shows that the battery has completed charging, resistor R5 programs the charging current to the battery. The DW01 IC is a protection circuit for charging the battery. It has two control pins (OC and OD) that actuate the two mosfets of the FS8205. The OD pin (over discharge) is used to turn off Q1 if the battery voltage drops below 2.4V, and the OC pin (over charge) is used to turn off Q2 if the battery voltage reaches 4.3V. It also protects against short circuit and overcurrent. This circuit forming IC4 (DW01-P) and Q1 (FS8205A) is optional. Only added for safety because Li-ion batteries can catch fire. If you only use the circuit formed by Ic2 (TP4056), just jumper SJ2 (GND-bat), removing the protection formed by DW01. You will not use IC4, Q1, C11, R11, R7.

Power Supply
The power supply is either a 5V supply with good filtering or a 3.7V Li-ion battery, the USB will also be used for charging the battery. When connecting the USB cable, the battery will be charged and the board will be powered by the 5V voltage. If you use a cell phone charger or computer USB, you will have a lot of noise in the circuit, in which case you can hear the FM band, but you may have noise on AM and SW. To power the SI4735/32 IC was used IC1 (XC6206P332) being a high precision LDO voltage regulator with input up to 6V and output 3.3V, used LC filter, and we have the voltage “+3V3-RF”. The OLED display requires 3.3V voltage, and we use the voltage provided by the Arduino mini PRO which should be the 3.3V and 8 MHz version. To power the audio amplifier CI either directly from the battery or from the 5V power supply.

The antenna input of the SI4735/32 is configured to share the 56 cm telescopic type antenna, between the SW and FM bands, and for AM you should use a ferrite antenna. L5 (4.7 µH) is an inductor, which with the Si4734/35 varactor (set to 1) acts as a low-pass filter peaking in the SW band. This inductor value is chosen assuming a 12pF capacitance of the telescoping antenna, C2 of 18 pF makes the AC coupling for FMI input, the AMI input capacitance is 7 pF (CAMI) and the parasitic capacitance is 8 pF on the board (CPAR). If either of these values change, the inductor has to be adjusted to peak in the SW band (desired peak at 23 MHz). D1 and D2 are for ESD protection and should be of the type with at most 1pF parasitic capacitance, especially for the FM band. C4 of 470nF couples the AM and SW signal to the AMI input. C1 33pF with a ferrite antenna or a fixed 220uH inductor blocks the AM (MW) band.

FB1 (180 nH) is the tuning inductor for FM (Optional for FM application only). This inductor together with the telescopic antenna capacitance(~22 pF in the center of the FM band), the 18 pF AC coupling capacitor (C2) and the typical 5 pF FMI input capacitance (CFMI) resonates in the FM band. If any of the capacitance values change, the inductor has to be adjusted to peak in the FM band (desired peak at 100 MHz).

Switch S1 toggles between AM and SW.

This circuit is optional.

For AM (MW) reception you can use 180-450 µH ferrite antennas, the signal will be coupled via 470nF C4, D2 (BAV99) does ESD protection, especially if the antenna is external type. You can also use a loop antenna for AM, in which case you will need a 1:6 transformer to adapt impedance.

For FM reception, use a telescopic type antenna.

For shortwave (SW) reception, you can use a telescopic antenna shared with FM or a medium wave antenna. If the SW antenna is not shared with FM, change C2 to 1nF, Fb1 to 56nH, and remove L5.

The 32.768KHz crystal can be a conventional cylindrical PTH or SMD 3.2×1.5.

Jumper SJ1 connects the SEN pin to VCC or GND.

The digital audio outputs are not connected, but may be performed in the future.

The audio outputs are AC coupled by C15 and C16 and connected to the headphone amplifier IC TDA1308 which is connected to J3, IC5 will be used as a high-quality headphone amplifier or preamplifier for the next audio stage. Connecting the headphone will disconnect the output to the speaker. If you prefer not to use this headphone amplifier stage, simply install the 0 Ohm resistors R9 and R10 or simply jumper it at this point. In normal use, R9 and R10 will not be used. If you are not going to use the headphone amplifier, do not install IC5, R14, R15, R16, R17, C21, C22, C25, C28, C23, C24, and install R9 and R10.

For audio amplification IC 8002 was used (IC6 and IC7) that will provide up to 2W per channel at 5V, in case you are going to use it as mono just install IC7 and make a jumper in SJ3. In this case, do not use IC6, C27, R26, C29, R31, C33. You may need to change the gain of the audio amplifier ICs depending on the manufacturer.

Some display modules may have different pin layouts.

Some display modules may have different pin layouts.

About the keys:
AGC – Automatic gain control active or choose attenuation.
BW – Frequency bandwidth
BAND – Choose frequency range.
VOL – Adjusts volume
STEP – Frequency step
MODE – Mode, switch to SSB, USB.

The encoder key works together with the keys, pressing the encoder key selects the function.

The arduino mini PRO should be 3.3V 8MHz, and to record you should use a USB/TTL converter module, here I used FT232RL. You should have the Arduino software installed and install the PU2CLR SI4735 Library for Arduino, see how here.

If you use SI4732 you must solder on the bottom of the board, the other components are soldered on top.

Printed circuit board suggestion to assemble the all-band digital radio

Si4735 Pcb Bottom Layer Fm Am
Si4735 Pcb Bottom Layer
Si4735 Pcb Arduino Bottom Overlay
Si4735 Pcb Top Layer
Si4735 Pcb Component Viewer Top
Si4735 Pcb Component Viewer Top
Si4735 Pcb Component Viewer- Bottom
Si4735 Pcb Component Viewer-Bottom
Si4735 Pcb Arduino Top Overlay
Si4735 Pcb Top Overlay

BOM for assembling the all-band radio with SI4735 or SI4732 and Arduino

Last Update: 26/01/2022 16:15

R1, R21 (1R0)Resistor SMD 12062
R3, R4, R111K (102)Resistor SMD 08053
R51.5K (152)Resistor SMD 08051
R7100 (101)Resistor SMD 08051
R810 (100)Resistor SMD 08051
R9, R100 (Optional) (0)Resistor SMD 08052
R12, R13, R18, R19, R20, R21, R24, R30, R33, R3410K (103)Resistor SMD 080510
R14, R153.9K (392)Resistor SMD 08052
R16, R1747K (473)Resistor SMD 08052
R22, R23, R2722k (223)Resistor SMD 08053
R26, R3120k (203)Resistor SMD 08052
R3268k (683)Resistor SMD 08051
C133pFCeramic Capacitor SMD NP0 08051
C218pFCeramic Capacitor SMD NP0 08051
C3, C61uCeramic Capacitor SMD 08052
C4470nFCeramic Capacitor SMD 08051
C5, C910uF/16VElectrolytic capacitor2
C7, C822pFCeramic Capacitor SMD NP0 08052
C10, C11, C13, C17, C24, C33, C34100nCeramic Capacitor SMD 08057
C1222nFCeramic Capacitor SMD 08051
C14, C18, C2347uF/16VTantalum Capacitor 35283
C15, C164.7uFCeramic Capacitor SMD 08052
C19, C20, C3510nCeramic Capacitor SMD 08053
C21, C22100pCeramic Capacitor SMD 08052
C25, C26100uF/16VElectrolytic capacitor2
C27, C28220nCeramic Capacitor SMD 08052
C29, C301uFCeramic Capacitor SMD 08052
C321000uF/10VElectrolytic capacitor SMD 8×101
D1, D2BAV99 (A7) or equivalentDiode Switching SOT-23 1,5pF CT, 70V2
D3SS14 or equivalentDiode Schottky 1A 40V1
DSP1DISPLAY-OLED-128×64-I2COLED Display Module I2C IIC 128×641
LED1ChargLED 0805 Red1
LED3St-byLED 0805 Green1
Q1FS8205ADual Channel N Mosfet TSSOP-81
Q2AO3401A or equivalentMosfet canal P 30V 4A SOT-231
IC1XC6206P332MRVoltage regulator 3.3V SOT-231
IC2TP4056Battery Charger ESOP-81
IC3SI4735-D60SSOP24-N integrated radio receiver circuit1
IC4DW01Battery Protector SOT23-6L1
IC5TDA1308 or PT2308 (Optional)Headphone amplifier SOIC-8_150mil1
IC6, IC7FM8002E or equivalentAudio Amplifier 2W SOIC-8_150mil2
IC8SI4732-A10-GS (Optional)Integrated SOIC-16 radio receiver circuit1
Switch and connectors
S1K3-1260D-F1 or equivalentSwitch 2 positions, sliding – Korean Hroparts Elec1
S2SPPJ310500 or equivalentPush Buttons – ALPSALPINE1
S3MODETactile key1
S4BWTactile key1
S9STEPTactile key1
S10AGCTactile key1
SW1EC12E or equivalentRotary Encoder1
CN1BAT — BatteryJst Xh 2-Way Connector, 2.54 mm pitch or equivalent.1
CN2ROUT — Audio output right channelJst Xh 2-Way Connector, 2.54 mm pitch or equivalent.1
CN3LOUT — Audio output left channelJst Xh 2-Way Connector, 2.54 mm pitch or equivalent.1
J2U-F-M5DD-Y-1 or equivalentUSB SMD Micro-B Connector – Korean Hroparts Elec1
J3PJ-342C or equivalentP2 stereo SMD connector – XKB Connectivity1
J4DOSIN-801-0084 or equivalentBNC connector – Dosinconn1
FB1180nHInductor 08051
L2220uH (Optional)Inductor SMD 20121
L310uhInductor SMD 1812 >100mA1
L410uHInductor SMD DR74 >200mA1
L54.7uH (Optional)Inductor SMD 1206 – Q of 20 or greater at 25 MHz and minimal DC
Y1 or Y1B32.768KHz2 × 6 cylindrical PTH crystal or SMD 3.2×1.51
Solder, Wires, PCB, case, power supply, 3.7V Li-Ion battery, knob, etc.

Some components are optional, check the text.

Download the files for this assembly, including the board in PDF, PNG, PS and Gerber format, and the files for Arduino.



PU2CLR SI4735 Library for Arduino documentation

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About the author blog author. Electronics technician for the technical school of Brasilia - Brazil. Interested in electronics, circuits and technology in general.

5 thoughts on “SI4735 SI4732 all band radio receiver LW MW FM SW”

  1. Tony
    I’m getting an error on the Arduino code. :(.text.startup+0xa4): undefined reference to `Rotary::Rotary(char, char)’
    I have the rotary library included
    Any ideas?

    • Dale, it seems like you are encountering an error in the Arduino code related to the Rotary library. The error message you mentioned, “undefined reference to `Rotary::Rotary(char, char)’,” suggests that there might be an issue with how you are initializing the Rotary object.

      To troubleshoot this, I would recommend checking the parameters you are passing to the Rotary constructor. Make sure that you are providing the correct data types and that the arguments match the constructor’s expected parameters. Double-checking the documentation or example code for the Rotary library might also be helpful in ensuring you are using it correctly.

      If you are confident that the code is correct and the issue persists, it is possible that there might be a problem with the library itself. In such cases, you could try reaching out to the library’s developer or community for assistance. They might be able to provide insights or suggest alternatives to resolve the error.

      Overall, carefully reviewing the code, verifying the parameter values, and seeking support from the library’s resources should help you identify the cause of the error and find a solution.


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