PCF8591 I2C Analog I/O Expander Library

A simple and efficient library to use the PCF8591 I2C 8-bit A/D and D/A converter with Arduino, ESP8266, ESP32, and other platforms. It provides 4 analog inputs and 1 analog output.

Author: Renzo Mischianti
Website: www.mischianti.org
GitHub: xreef/PCF8591_library

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📚 Documentation & Articles

Complete documentation, tutorials, and examples are available on mischianti.org.

• 🌐 PCF8591 Main Article: The primary guide for this library with wiring diagrams and detailed explanations.
• 🛠️ I2C Scanner: A utility to find the I2C address of your device.
• 💬 Support Forum (English): Get help and discuss the library.
• 💬 Forum di Supporto (Italiano): Ottieni supporto e discuti della libreria.

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📋 Table of Contents

• Features
• Supported Platforms
• Installation
• Hardware Setup
• API Overview
• Basic Usage
• Advanced Reading Modes
• Voltage Functions
• Changelog
• License
• Contributing
• Support & Contact

✨ Features

• 4 Analog Inputs: Read up to 4 analog channels over I2C.
• 1 Analog Output: Provides a true analog voltage output.
• 8-Bit Resolution: Both ADC and DAC operate at 8-bit resolution (0-255).
• Multiple Input Modes: Supports four single-ended inputs, three differential inputs, and combined modes.
• Efficient Reading: Read all 4 input channels in a single I2C transaction with analogReadAll().
• Voltage Conversion: Built-in functions (voltageRead, voltageWrite) to work directly with voltage levels.
• Flexible I2C Configuration: Custom I2C pins (SDA, SCL) can be specified for platforms like ESP8266/ESP32.

🎯 Supported Platforms

Platform	Support	Notes
ESP32	✅	Full support
ESP8266	✅	Full support
Raspberry Pi Pico (RP2040)	✅	Full support
Arduino (AVR, Uno, Mega, UNO R4)	✅	Full support
Arduino SAMD (Nano 33 IoT, etc.)	✅	Full support
STM32	✅	Full support

📦 Installation

Arduino IDE (Library Manager)

1. Open Arduino IDE.
2. Go to Sketch > Include Library > Manage Libraries....
3. Search for "PCF8591_library" by Renzo Mischianti.
4. Click Install.

PlatformIO

Add the library to your platformio.ini file:

lib_deps = xreef/PCF8591 library

Manual Installation

1. Download the latest release from GitHub.
2. Unzip the folder and rename it to PCF8591_library.
3. Move it to your Arduino libraries folder.
4. Restart the Arduino IDE.

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🔌 Hardware Setup

Here is a typical wiring diagram for the PCF8591 module.

And here is the pinout of the IC:

🚀 API Overview

Constructor

// Basic constructor with I2C address
PCF8591(uint8_t address);

// For ESP8266/ESP32 with custom SDA/SCL pins
PCF8591(uint8_t address, uint8_t sda, uint8_t scl);

Core Functions

// Initialize the library (must be called in setup())
bool begin();

// Read all 4 analog inputs at once
PCF8591::AnalogInput analogReadAll();

// Read a single analog input channel
int analogRead(uint8_t channel, uint8_t mode = FOUR_SINGLE_ENDED);

// Write a value (0-255) to the analog output
void analogWrite(uint8_t value);

// Read the voltage from a specified analog pin
float voltageRead(uint8_t analogPin, bool microcontrollerReferenceVoltage = true, float referenceVoltage = 5.0);

// Write a voltage level to the analog output
void voltageWrite(float value, bool microcontrollerReferenceVoltage = true, float referenceVoltage = 5.0);

💡 Basic Usage

Here is a simple example of how to read an analog input and write to the analog output.

#include <Wire.h>
#include <PCF8591.h>

// Set I2C address (e.g., 0x48)
PCF8591 pcf8591(0x48);

void setup() {
  Serial.begin(115200);

  // Initialize the PCF8591
  if (!pcf8591.begin()) {
    Serial.println("Couldn't find PCF8591");
    while (1);
  }

  Serial.println("PCF8591 initialized!");
}

void loop() {
  // Write a value (e.g., 128) to the analog output
  pcf8591.analogWrite(128);

  // Read a single analog input (AIN0)
  int analogValue = pcf8591.analogRead(AIN0);
  Serial.print("Value from AIN0: ");
  Serial.println(analogValue);

  // Read all analog inputs at once
  PCF8591::AnalogInput allValues = pcf8591.analogReadAll();
  Serial.print("AIN0: "); Serial.print(allValues.ain0);
  Serial.print(" | AIN1: "); Serial.print(allValues.ain1);
  Serial.print(" | AIN2: "); Serial.print(allValues.ain2);
  Serial.print(" | AIN3: "); Serial.println(allValues.ain3);

  delay(500);
}

🔬 Advanced Reading Modes

The PCF8591 supports different analog input configurations, which can be selected using the analogRead function.

// Example: Read the differential value between AIN0 and AIN1
int differentialValue = pcf8591.analogRead(CHANNEL0, THREE_DIFFERENTIAL_INPUT);

// Example: Read AIN0 as single-ended and AIN1, AIN2 as differential
int value = pcf8591.analogRead(CHANNEL0, AIN0_SINGLE_AIN1_AIN2_DIFFERENTIAL);

⚡ Voltage Functions

The library provides helper functions to work directly with voltage values, abstracting the 8-bit conversion.

void setup() {
  // ... setup code ...
  pcf8591.begin();
}

void loop() {
  // Set the analog output to 2.7 Volts
  // Assumes the microcontroller VCC is the reference voltage.
  pcf8591.voltageWrite(2.7);

  delay(1000);

  // Read the voltage from analog input AIN0
  float inputVoltage = pcf8591.voltageRead(AIN0);
  Serial.print("Voltage at AIN0: ");
  Serial.print(inputVoltage);
  Serial.println(" V");

  delay(1000);
}

📝 Changelog

• 31/10/2025: v1.1.3 Minor change and README update
• 01/02/2024: v1.1.2 Add the possibility to insert address at begin() function
• 10/07/2023: v1.1.1 Add support for Arduino UNO R4
• 16/02/2023: v1.1.0 Fix STM32 support, add support for RP2040, and add custom SERCOM for SAMD.
• 06/04/2022: v1.0.2 Fix package size

📄 License

This library is released under the MIT License. See the LICENSE file for more details.

Copyright (c) 2019-2025 Renzo Mischianti

🤝 Contributing

Contributions are welcome! Please fork the repository, create a feature branch, and submit a pull request.

📞 Support & Contact

• Documentation: https://www.mischianti.org/category/my-libraries/pcf8591-i2c-analog-expander/
• GitHub Issues: https://github.com/xreef/PCF8591_library/issues
• Author: Renzo Mischianti (@xreef)

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⭐ If this library helped your project, please give it a star on GitHub!