QN8066

QN8066 FM DSP RX/TX Arduino Library

This library is intended to provide an easy-to-use interface for controlling the QN8066 FM transceiver and receiver.

The primary goal of this Arduino library project for the QN8066 is to simplify the development of robust applications using this device. I hope that hobbyists, electronics technicians, radio amateurs, and others interested in this work will find success in their projects. All the C/C++ funcions and methods are documented [here].(https://pu2clr.github.io/QN8066/extras/apidoc/html/index.html)

This library can be freely distributed using the MIT Free Software model. By using or installing Library you are agreeing to the terms of the MIT licence.

Copyright (c) 2024 Ricardo Lima Caratti.

Contact: pu2clr@gmail.com.

About Me

I hold a Master’s degree in Educational Technology from the Federal University of Ceará, where I delved into the ways technology can enhance learning experiences. My passion for computer science led me to specialize in it, focusing on Distributed Systems Development with an Object-Oriented approach, at the University of Brasília. My academic journey began with a Bachelor’s degree in Information Systems from the União Pioneira de Integração Social (UPIS-Brasília). Outside the classroom, my main hobbies are electronics and Amateur Radio.

Notice to Users Regarding this Library

This library is continuously evolving, with both corrective and feature updates. While the implemented functions have been tested, it is possible that in certain situations, the library may exhibit unexpected behavior. I encourage users to always utilize the latest release of this library. Should you encounter any issues, please feel free to contact me at pu2clr@gmail.com. I will do my best to address or clarify any problems as quickly as possible. Thank you.

Contents

  1. Legal Compliance Guidelines
  2. QN8066 Arduino Library Features
  3. Technical Overview of the QN8066 RX/TX Device (IC)
  4. Why a QN8066 library for Arduino?
  5. Groups and Forums
  6. QN8066 Functional Blocks
  7. QN8066 PINOUT
  8. QN8066 Summary of User Control Registers
  9. Homemade setup with the QN8066
  10. DIY Kit 5W-7W FM Transceiver
  11. Arduino Library Documentation
  12. Arduino Sketch examples
  13. Boards where this library can be compiled
  14. Donate
  15. Most Frequent Problems
  16. References

Important Notice

Please, be aware that the use of FM transmitters is regulated by the laws and regulations of each country. It is crucial to ensure that your use of any FM transmitter complies with the applicable legal requirements and does not violate any broadcasting regulations.

  1. Frequency Range: Ensure that the frequency range used by your FM transmitter is permitted in your country.
  2. Transmission Power: Adhere to the maximum allowed transmission power to avoid interference with licensed broadcasters and other communication services.
  3. Licensing: Check if a license is required to operate an FM transmitter in your region. Obtain the necessary permissions if required.
  4. Interference: Avoid causing interference with other electronic devices and communication services. Ensure your setup follows the prescribed technical standards.
  5. Public Safety: Be mindful of public safety and ensure your use of the FM transmitter does not pose any risks.

By following these guidelines, you can ensure that your use of the FM transmitter respects the laws and regulations of your country and does not result in any legal issues.

Groups and Forums

There is a Facebook group called QN80XX FM Transmitters & Receivers Enthusiasts where the purpose is exchanging experiences with projects based on Quintic QN80XX IC family. You will be welcome there.

Acknowledgements

Why a QN8066 library for Arduino?

Technically, no Arduino application strictly requires a library. In some cases, avoiding libraries might even be the right decision. However, there are several compelling reasons to consider using them.

Libraries often simplify the design and maintenance of code, and they can make your projects more portable by implementing the necessary functionality across multiple hardware platforms.

For example, if you want to use an LCD or another display device in a project that monitors temperature and atmospheric pressure, there are many excellent libraries available for Arduino users. These libraries usually include most, if not all, of the features you might need. Re-inventing the wheel by not using a library generally doesn’t make sense—unless you need a feature that no existing library supports. Using a library is often the smarter choice, particularly when it can simplify porting your code to different hardware.

Utilizing a library can reduce programming complexity and enhance the robustness of your application. It simplifies life not only for other developers but also for yourself. You don’t need to be a software engineer to see the value in this. A library is similar to an integrated circuit (IC); while you could manually implement the functionality of many ICs in a circuit, doing so would significantly increase the cost, complexity, size, and potential for failure of your project. Often, it’s better to abstract certain functions inside a ready-made IC. The user only needs to know how to interact with the chip, not how the chip itself is designed.

Finally, if you’re already using libraries to handle the I2C bus (Wire.h), TFT or OLED displays, SPI devices, and Serial UART communication, it makes sense to use a library to manage the QN8066 device as well. The QN8066 Arduino Library can add convenience, development speed, and robustness to your project. Unlike closed-source solutions, this library is open-source, allowing you to learn from and modify the code as needed.

QN8066 Arduino Library Features

This library uses the I²C communication protocol and implements most of the functions offered by QN8066 IC from QUINTIC. This library also has primitive functions that make it easier for you to implement commands that may not have been implemented yet. As said before, this library is constantly improving. Check the API documentation before implementing a new function. It is likely that your function is already implemented. See the API documentation for this library.

  1. Open Source. It is free. You can use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software. See MIT License to know more.
  2. Built based on QN8066 Datasheet
  3. C++ Language and Object-oriented programming. You can easily extend the QN8066 class by adding more functionalities.
  4. API Documentation. All functions implemented in this library have documentation that can be checked in the source code or at this link
  5. Available on Arduino IDE (via Manage Libraries). Easy to install and use.
  6. Cross-platform. You can compile and run this library on most of boards supported by the Arduino IDE (Examples: ATtiny85, boards based on ATmega328 and ATmega-32u4, ATmega2560, ARM Cortex, STM32, Arduino DUE, ESP32 and more).
  7. Simplifies projects based on QN8066
  8. A lot of examples to guide the user
  9. RDS support
  10. Clock reference selection

Technical Overview of the QN8066 RX/TX Device (IC)

Introduction

The QN8066 is a highly integrated and versatile receiver/transmitter (RX/TX) device designed for use in FM radio applications. It offers a comprehensive solution for high-quality audio reception and transmission with minimal external components, making it suitable for a wide range of applications, including portable radios, automotive systems, and multimedia devices.

Key Features

Technical Specifications

Applications

QN8066 Functional Blocks

Functional Blocks

  1. RF Front-End: The RF front-end is designed to efficiently capture and process FM signals, ensuring minimal loss and high-quality signal reception.
  2. PLL Synthesizer: The phase-locked loop (PLL) synthesizer ensures stable frequency generation and accurate tuning.
  3. Audio Processing: Includes both analog and digital audio processing units to enhance sound quality and support various audio formats.
  4. Power Management: Advanced power management features optimize power consumption, making the QN8066 ideal for portable applications.

Attention

QN8066 PINOUT

QN8066 PINOUT

QN8066 Pin Descriptions

SSOP16 PIN NAME DESCRIPTION  
1 SCL Clock for I2C serial bus  
2 SDA Bi-directional data line for I2C serial bus  
3 VCC Voltage supply  
4 ALO Analog audio output – left channel  
5 ARO Analog audio output – right channel  
6 GND Ground  
7 RFI FM Receiver RF input  
8 GND Ground  
9 ARI Right channel audio input  
10 ALI Left channel audio input  
11 GND Ground  
12 RFO Transmitter RF output – connect to matched antenna  
13 CEN Chip enable with internal pull up: Chip power down if less than 0 4V and VIO is powered; power up if higher voltage or left floated
14 XCLK External clock input  
15 GND Ground    
16 INT Interrupt output, active low, need pull-up externally  

QN8066 Summary of User Control Registers

REGISTER NAME USER CONTROL FUNCTIONS  
00h SYSTEM1 Sets device modes  
01h SYSTEM2 Sets external clock type and CCA parameters  
02h CCA Sets CCA parameters  
03h SNR Estimate RF input CNR value  
04h RSSISIG In-band signal RSSI dBµ V value  
05h CID1 Device ID numbers  
06h CID2 Device ID numbers  
07h XTAL_DIV0 Frequency select of reference clock source  
08h XTAL_DIV1 Frequency select of reference clock source  
09h XTAL_DIV2 Frequency select of reference clock source  
0Ah STATUS1 System status  
0Bh RX_CH Lower 8 bit of 10-bit receiver channel index  
0Ch CH_START Lower 8 bits of 10-bit channel scan start channel index  
0Dh CH_STOP Lower 8 bits of 10-bit channel scan stop channel index  
0Eh CH_STEP Channel scan frequency step Highest 2 bits of receiver channel indexes
0Fh RX_RDSD0 RDS data byte 0  
10h RX_RDSD1 RDS data byte 1  
11h RX_RDSD2 RDS data byte 2  
12h RX_RDSD3 RDS data byte 3  
13h RX_RDSD4 RDS data byte 4  
14h RX_RDSD5 RDS data byte 5  
15h RX_RDSD6 RDS data byte 6  
16h RX_RDSD7 RDS data byte 7  
17h STATUS2 Receiver RDS status indicators  
18h VOL_CTL Audio volume control  
19h INT_CTRL Receiver RDS control  
1Ah STATUS3 Receiver audio peak level and AGC status  
1Bh TXCH Lower 8 bit of 10-bit transmitter channel index  
1Ch TX_RDSD0 Transmit RDS data byte0  
1Dh TX_RDSD1 Transmit RDS data byte1  
1Eh TX_RDSD2 Transmit RDS data byte2  
1Fh TX_RDSD3 Transmit RDS data byte3  
20h TX_RDSD4 Transmit RDS data byte4  
21h TX_RDSD5 Transmit RDS data byte5  
22h TX_RDSD6 Transmit RDS data byte6  
23h TX_RDSD7 Transmit RDS data byte7  
24h PAC PA output power target control  
25h FDEV Specify total TX frequency deviation  
26h RDS Specify transmit RDS frequency deviation  
27h GPLT Transmitter soft chip threshold, gain of TX pilot  
28h REG_VGA TX AGC gain  

Homemade setup with the QN8066

The following figures illustrate a homemade setup with the QN8066. As you can see, only a few components are needed to build an FM transmitter with the QN8066. The key component is the 32.768 kHz active crystal (32,768 Hz). The QN8066 allows for other signal source configurations. As far as I understand, there is no possibility of using passive crystals. The QN8066 requires an active signal source provided by a generator.

Standalone QN8066 setup 0

Standalone QN8066 setup 1

Standalone QN8066 setup 2

Through some functions in the Arduino library, you can configure the active crystal you intend to use. Check the setup and begin functions for more details.

The table below shows some tested sources (active crystal or signal generator) and divider values.

Source (kHz) Divider
32.768 1
< 1,310.720 did not work
1,310.720 40
1,638.400 50
3,276.800 100
13,107.200 400
16,384.000 500
32,768,000 1000

Example 1

/**

This sketch works on Arduino Pro Mini, Nano, UNO, or any other board based on the ATMega328. 
IMPORTANTE: Refer to the documentation if you are using a 5V microcontroller instead of a 3.3V one.

This sketch illustrates the clock configuration used on the XCLK pin of the QN8066. 
Depending on the active crystal or signal generator you are using, it is important 
to set the correct frequency and signal waveform type for the QN8066 to function 
properly.

IMPORTANT: The QN8066 works with active crystals or signal generators. 
           Passive crystals will not work with the QN8066.

Author: Ricardo Lima Caratti (PU2CLR) - 2024
*/

#include <QN8066.h>
#define FREQUENCY 1069 // 106.9 MHz 
QN8066 tx;
char str[80];
void setup() {
  Serial.begin(9600);
  while (!Serial) ;
  delay(100); // Wait a bit while the system stabilizes.
  if (!tx.detectDevice()) {
    Serial.println("\nDevice QN8066 not detected");
    while (1);
  }
  // The call to the setup function below illustrates the use of a 32.768 kHz crystal. 
  // Since the reference clock for the QN8066 is exactly 32.768 kHz, you can provide the 
  // frequency value of the crystal you are using divided by 32.768. 
  // For example: if you are using a 32.768 kHz active crystal, then you should provide the 
  // divisor value of 1. If the signal generator (active crystal) produces a sine wave, 
  // enter the value 0, and if it is a digital signal, you should enter the value 1. See below.  
  tx.setup(1,      // Divider based on frequency select of reference clock source. The crystal used here is 32.768 kHz  
           false,  // Mono False => TX will start in stereo mode
           false,  // TX will start in RDS OFF
               1,  // PreEmphasis = 75
               1); // 1 if XCLK pin is receiving a digital clock. set it to 0 if you are using a sine-wave oscillator. 

  tx.setTX(FREQUENCY);    // Chenge the FREQUENCY constant if you want other value
  sprintf(str, "\n\nBroadcasting...");
  Serial.print(str);
}
void loop() {
    sprintf(str,"\nFSM: %d\nAudio Peak: %d mV", tx.getFsmStateCode(), tx.getAudioPeakValue());
    Serial.print(str);
    tx.resetAudioPeak();
    delay(15000);
}

Example 2


#include <QN8066.h>
#define FREQUENCY 1069   // 106.9 MHz 
QN8066 tx;
char str[80];
void setup() {
  Serial.begin(9600);
  while (!Serial) ;
  delay(100); // Wait a bit while the system stabilizes.
  if (!tx.detectDevice()) {
    Serial.println("\nDevice QN8066 not detected");
    while (1);
  }
  tx.begin();
  // Assuming you are using a 32.768 kHz active crystal, a digital signal, and LO<RF, 
  // the image is on the lower side.
  tx.setXtal(1,1,0); 
  // tx.setXtal(100,1,0); // If you are using 3,768 active crystal
  // tx.setXtal(1000,1,0); // If you are using 32,768,000 active crystal
  delay(100);
  tx.setTX(FREQUENCY);    // Chenge the FREQUENCY constant if you want other value
  sprintf(str, "\n\nBroadcasting...");
  Serial.print(str);
}
void loop() {
    sprintf(str,"\nFSM: %d\nAudio Peak: %d mV", tx.getFsmStateCode(), tx.getAudioPeakValue());
    Serial.print(str);
    tx.resetAudioPeak();
    delay(15000);
}

DIY Kit 5W-7W FM Transceiver

It is possible to find Transceivers based on the QN8066 in kit form. With this library, you will also be able to control this kit, thereby expanding its original functionalities. Check AliExpress and others to check it out.

The images below show the DIY Kit 5W-7W FM Transceiver available on AliExpress.

DIY Kit 5W-7W FM Transceiver assembled without the RF final amplifier

DIY Kit 5W-7W FM Transceiver 01

DIY Kit 5W-7W FM Transceiver assembled in a homemade case

DIY Kit 5W-7W FM Transceiver 02

Using the QN8066 Arduino Library with DIY Kit 5W-7W FM Transceiver

The code below is a minimalist sketch example of using this library with the DIY Kit 5W-7W FM board.

Arduino and the Kit 5W-7W FM connections

Anduino Nano or Uno pin Kit 5W-7W FM
GND GND
D9 PWM (*1)
A4 SDA (*2)
A5 SCL (*2)
(1) Communication Issue During PWM Signal Generation

During experiments, commands sent to the QN8066 via I2C often had no effect, such as switching from “Stereo” to “Mono” or changing the transmission frequency. To resolve this, disable the PWM (0% duty cycle) before sending commands and re-enable it afterward.

#include <QN8066.h>
QN8066 dv;
void setup() {
  Serial.begin(9600);
  while (!Serial); 
  pinMode(9, OUTPUT);  // Pin use to PWM power control
  dv.setup();
  Serial.print("\nStarting the system...");
  delay(1000);      
  dv.setTX(1067); // Set the transmitter to 106.9 MHz 
  dv.setTxStereo(true);
  // Now you can start PWM
  analogWrite(9, 50);  // It is about 1/5 of the max power (5~7W). It is between 1 and 1,4 W
  Serial.print("\nBroadcasting...");
  // Turning the Stereo OFF
  analogWrite(9, 0); // Disable PWM
  dv.setTxStereo(false);
  analogWrite(9, 50); // Enable PWM
}

void loop() {
}
(2) Compatibility Between the KIT and 5V Microcontroller Such as the Arduino Nano

The “DIY 5~7W FM Transmitter Kit” is designed for 3.3V controllers and has I2C pull-up resistors connected to its 3.3V power supply. However, the Arduino Nano operates at 5V, producing 5V signals on the I2C bus, which can cause communication instability. Additionally, the Nano cannot run stably on a 3.3V supply from the kit.

The simplest, but impractical, solution is to modify the Arduino Nano to run at 3.3V by changing its crystal to 8MHz and updating the bootloader. A better option is to use an Arduino Pro Mini 3.3V for direct compatibility.

In some examples using the Arduino Nano, a 3.3V to 5V voltage converter was added for power, along with two 150-ohm resistors in series with the I2C bus and two 10K resistors as pull-ups. While not ideal, this method works. A more appropriate solution would be to use a bidirectional I2C level shifter for compatibility.

The Arduino Nano is used in some examples in this library because it’s popular among hobbyists, many of whom already have one or an Arduino Uno with the same architecture. Most other examples use 3.3V microcontrollers that do not require any modifications.

See also DIY Kit 5W-7W FM example

DIY Kit 5W-7W FM connected with Arduino Pro Mini

The following figure shows the “DIY Kit 5W-7W FM TRANSMITTER” connected to the Arduino Pro Mini. The following link provides more operational details. Click here to watch the video.

DIY Kit 5W-7W FM Transceiver 02 Click here to see the source code and schematic

Some personal considerations about this KIT

Before presenting some observations that I consider important, it is worth highlighting that the following information may not reflect the reality in other environments or with other kits. The goal here is not to judge the quality of the kit or its architecture. However, these observations may explain some phenomena you might experience during the development of your project and help you mitigate these issues.

Based on several experiments I conducted with this kit, I observed instability in the communication between the microcontroller and the QN8066 via the I2C bus in the following situations:

  1. PWM Line Interference: When the PWM line to control the transmitter’s power is active, communication failures and even unavailability of the QN8066 to respond to new commands are common. One solution to this problem was to disable the PWM signal every time a command is sent to the system and re-enable the PWM signal afterward. It is important to note that this behavior hinders or limits, to some extent, a more dynamic use of RDS services.

  2. High Power Transmission: When the transmitter is configured to transmit at higher power levels, approaching its upper limit of 7W, the communication also becomes unstable, and the QN8066 stops responding to the microcontroller, even though it continues to transmit.

  3. Avoid touching: Touching certain points on the KIT board or the microcontroller with your hands can also cause system instability.

  4. Wire-up organization: Shortening and organizing the I2C bus lines that connect the KIT to the microcontroller significantly improves system stability.

  5. Good grounding: Through good grounding, it was possible to make the system more stable.

  6. System Stability of the KIT Powered via Microcontroller (Tests and Results): Without using the power module, that is, by only powering the QN8066 stage of the board through the interface connector with the microcontroller, the system remains stable. The example sketches provided in this library ran for hours without any instability. The sketch developed for the Arduino Pro Mini and LCD16x2 was subjected to a test lasting over 16 hours without any issues.

  7. Impact of RF Interference on I2C Communication in Power Control Systems: There is another point to consider that might somewhat absolve the issue of power control via I2C. As the bandwidth increases, the transmitter’s power also rises. It’s possible that excessive RF signal in close proximity to the circuit is disrupting the I2C communication. When using a “dummy load,” there is a noticeable reduction in I2C communication errors. This can be demonstrated by eliminating the I2C control and manually controlling it by applying a voltage of 3.3V or lower to the power control line. In my experiments, the I2C communication errors persisted, causing system instability.

  8. Enhancing System Stability Through Shielding and Isolation (Future Testing Considerations): Finally, I believe that good shielding of the KIT in a metal enclosure, as well as isolating the microcontroller from the transmitter (in a separate enclosure), could significantly improve the system. This is something to be tested in the future.

The following are some references to reports that may align with what was previously mentioned.

It is important to highlight that this library was not developed exclusively to work with this kit. In fact, it was designed to work with any architecture involving the QN8066 via the I2C protocol. That said, it is crucial for the designer or experimenter to keep in mind the necessary precautions to provide a stable system. There are various literatures that can help follow the best design practices involving I2C communication.

Considerations

In a new project involving the QN8066, I believe a more stable approach would be not to work with power levels above ½W on the same board. An additional amplification module could be added separately from the QN8066 circuit. The organization of the printed circuit board is also a determining factor in improving the stability of the system. Preferably, the communication circuit of the microcontroller with the QN8066 should be as far away as possible from the RF circuit. The appropriate values for the pull-up resistors for the I2C bus is a variable that deserves attention. These values may depend on the length of the bus and other I2C devices that may be connected to the circuit. In my experiments, I used 10K pull-up resistors. However, lower resistance values can be tested and may further improve the stability of the system. Consider shielding the Display and microcontroller circuit so that unwanted signals and interference do not propagate to the QN8066 circuit.

Boards where this library can be compiled

This library can be useful to develop cross-platform software.

The table below shows the some boards where this library has been successfully compiled.

  Board Need voltage converter I²C Pins Used Reset Pin Features
1 Arduino Pro Mini 3.3V 8MHz No A4 and A5 12 More…
2 Mega 2560 Pro Yes 20 and 21 12 More…
3 ESP WEMOS LOLIN32 No GPIO21 and GPIO22 [4] GPIO25 [5] More…
4 ESP32 Dev Module No GPIO21 and GPIO22 [4] GPIO25 [5] More…
5 ESP32 Wrover Module No GPIO21 and GPIO22 [4] GPIO25 [5] More…
6 ESP8266 No GPIO4 and GPIO5 GPIO2 More…
7 Arduino UNO Yes A4 and A5 12 More…
8 Arduino NANO ATmega 328 Yes A4 and A5 12 More…
9 Arduino NANO ATmega 168 Yes A4 and A5 12 More…
10 Arduino NANO 33 IoT No [6] A4 and A5 12 More…
11 Arduino Yún / ATmega-32u4 Yes 2 and 3 12 More…
12 ATtiny84 No 7 and 8 6 More…
13 ATtiny85 No 5 and 7 2 (D3) More…
14 Arduino DUE No 2 and 3 12 More…
15 BlueDuino 3.3V (ATmega-32u4) No 2 and 3 10 More…
16 Arduino Mini Pro 5V 16Mhz Yes 2 and 3 10 More…
17 STM32F746G-DISCO No - - More…
18 STM32F103 Series No PB6 (SCL) and PB7(SDA) PA12 More…
19 STM32F411 Series No PB6 (SCL) and PB7(SDA) PA12 More…
20 Raspberry Pi Pico No GP0 (0) and GP1 (1) GP16 (16) More…
21 WeAct Studio RP2040 Pico No GP0 (0) and GP1 (1) GP16 (16) More…
22 Seeeduino XIAO No A4 and A5 3 More…
23 Teensy 3.1 No A4 and A5 12 More…
24 Teensy 4.1 No A4 and A5 12 More…
25 Atmega8 No PC4 and PC5 PD6 More…
26 Atmega32 No PC1 and PC0 PB2 More…
27 Atmega128 No PC1 and PC0 PB2 More…
28 LGT8F328P No A4 and A5 12 More…
29 LUATOS ESP32C3 No GPIO4 and GPIO5 GPIO8 More…

If you find this project useful, consider making a donation so that the author of this library can purchase components and modules for improvements and testing of this library. Click here to donate or use the QR code below.

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Most Frequent Problems

  1. Avoid using a computer connected to the mains during testing. The electrical grid can disturb the communication between the Arduino based board and the QN8066 device.
  2. Check the I2C bus pull-up resistors.
  3. Check the voltage on the digital pins of the QN8066. It is not be greater than 3.6V.
  4. If you are using the Arduino Pro Mini 3.3V (8MHz), check the correct board on Arduino IDE Tools menu, Processor: “Atmega328P (3.3V, 8MHz)”. By default, the Arduino IDE uses the Pro Mini 5V processor version.
  5. Do not try to power an ATmega328 Arduino Board designed to work with 5V and 16MHz with a 3.3V supply. That configuration will make your system unstable. See ATmega328P Datasheet.
  6. Do not try to power your Arduino based board designed to work with 3.3V with greater voltage. See the technical specifications of your Arduino Board and remember that the maximum voltage of the QN8066 digital interface is 3.6V.
  7. During the implementation of your sketch, do not use high power (above 1/2 W) through an RF amplifier without proper shielding practices. The QN8066, particularly the I2C bus, is sensitive to spurious RF signals and may lose communication with the controller. Preferably, use a dummy load.
  8. Avoid using long wiring for the I2C connection.
  9. Good grounding: Through good grounding, it was possible to make the system more stable.

References

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