TCA9548A I2C Multiplexer with ESP32 Connect Multiple Devices

In this tutorial, we will learn about ESP32 I2C communication protocol using different I2C devices having same and different addresses. We will discuss how to use multiple I2C devices with ESP32 having the same address by incorporating a hardware solution. By using a TCA9548A I2C Multiplexer, we will be able to increase the I2C addresses of the modules with the same I2C address and thereby connect these devices on the same I2C bus. Additionally, we will interface ESP32 with different sensors and devices that communicate via I2C protocol and program our board to run an I2C scanner. This scanner will determine the number of I2C devices connected with ESP32. So let us begin!

We have a same guide with Arduino:

TCA9548A I2C Multiplexer Arduino Use Same Address I2C Devices

For general introduction of I2C protocol, you can refer to this guide:

I2C bus communication protocol

ESP32 I2C Pins

As mentioned earlier ESP32 has 2 I2C controllers which can be used to handle communication on an I2C bus. We can configure either as a master or slave. Now let’s see the default GPIO pins which are assigned to I2C controllers in the Arduino IDE library for ESP32.

The default I2C pin in ESP32 for SDA is GPIO21 and for SCL is GPIO22. If we want to change the GPIO pins we have to set them in code. The diagram below shows the pinout for the ESP32 which shows the default I2C pins.

The ESP32 I2C interface has the following features:

Standard mode (100 Kbit/s)
Fast mode (400 Kbit/s)
Up to 5 MHz, yet constrained by SDA pull-up strength
7-bit/10-bit addressing mode
Dual addressing mode

Now let’s see some examples. In the first section, we will see examples to connect different I2C devices which have different I2C addresses with ESP32. After that, we will see an example to connect the same I2C address devices with ESP32 using a TCA9548A 1-to-8 I2C multiplexer module.

Using Multiple Slave I2C Devices with ESP32 (I2C devices with different addresses)

In this section, we will first connect three different I2C devices (OLED, SHT32 (temperature sensor) and BME280 (temperature sensor)) with ESP32 using the default I2C pins. Then we will program our board to run an I2C scanner.

Components Required

ESP32 development board
SSD1306 OLED Display
BME280 sensor
SHT31 sensor
Breadboard
Connecting Wires

Interface ESP32 with OLED, BME280 and SHT31

Let us see how to connect ESP32 with an OLED, BME280 module, and SHT31 module together. We will use a common I2C line to connect all the devices. ESP32 will act as a master, and the BME280 sensor, SHT31 sensor, and the OLED will act as slaves.

The connections between the four devices which we are using can be seen in the table below.

ESP32	SSD1306 OLED Display	BME280	SHT31
3.3V	VCC	VCC	VCC
GPIO21	SDA	SDA	SDA
GPIO22	SCL	SCL	SCL
GND	GND	GND	GND

We have used the same connections as specified in the table above.

ESP32 with SHT31, BME280 and OLED schematic diagram

ESP32 I2C Scanner Arduino Sketch

Every I2C device has an address associated with it. ESP32 uses this address to communicate with the slave via I2C protocol.

Now copy this code and upload it your board with all the I2C devices already connected with it.

This code will scan for any I2C devices connected with ESP32 and will specify the number of devices with the address in the serial terminal.

#include <Wire.h>
 
void setup() {
  Wire.begin();
  Serial.begin(115200);
  Serial.println("\nI2C Scanner");
    byte error, address;
  int nDevices;
  Serial.println("Scanning...");
  nDevices = 0;
  for(address = 1; address < 127; address++ ) {
    Wire.beginTransmission(address);
    error = Wire.endTransmission();
    if (error == 0) {
      Serial.print("I2C device found at address 0x");
      if (address<16) {
        Serial.print("0");
      }
      Serial.println(address,HEX);
      nDevices++;
    }
    else if (error==4) {
      Serial.print("Unknown error at address 0x");
      if (address<16) {
        Serial.print("0");
      }
      Serial.println(address,HEX);
    }    
  }
  if (nDevices == 0) {
    Serial.println("No I2C devices found\n");
  }
  else {
    Serial.println("done\n");
  }
  delay(5000);  
  Serial.print("i2c devices found:");
  Serial.println(nDevices); 
}
 
void loop() {
      
}

The I2C scanner identified 3 devices connected to the I2C interface. The I2C Address of OLED Display is 0x3C, SHT31 is 0x44 and BME280 is 0x76.

As all of these three I2C devices had different addresses therefore it was possible to share the same I2C bus.

ESP32 Display BME280 and SHT31 Temperature Readings on OLED

As seen in the I2C scanner, BME280, SHT31 and OLED have different I2C addresses, hence it is possible to share the same I2C bus. Let us show you a sketch which accesses temperature readings from these two sensors and displays them on the OLED.

We will use Arduino IDE to program our ESP32 development board. Thus, you should have the latest version of Arduino IDE.

ESP32 Multiple I2C devices with different addresses Display temperature on OLED

Installing SSD1306 OLED Library in Arduino IDE

To use the OLED display in our project, we have to install the Adafruit SSD 1306 library in Arduino IDE. Follow the steps below to successfully install it.

Open Arduino IDE and click on Sketch > Library > Manage Libraries. The following window will open up.

Type ‘SSD1306’ in the search tab and install the Adafruit SSD1306 OLED library.

Install OLED SSD1306 Library Arduino IDE

Installing BME280 Arduino Library

As we are connecting the BME280 sensor with ESP32, therefore, we will have to install BME280 libraries to our module. We will require two libraries for this project:

We will use the Library Manager in our Arduino IDE to install the latest versions of the libraries. Open your Arduino IDE and go to Sketch > Include Libraries > Manage Libraries. Type Adafruit BME280 library name in the search bar and install them both.

Open your Arduino IDE and go to Sketch > Include Libraries > Manage Libraries. Type Adafruit unified sensor library name in the search bar and install it.

Install SHT31 Arduino Library

As we are also connecting the SHT31 sensor module with ESP32, therefore, we will have to install the libraries to access the sensor data. We will require two libraries for this project:

Adafruit SHT31
Adafruit BusIO

We will use the Library Manager in our Arduino IDE to install the latest versions of the libraries. Open your Arduino IDE and go to Sketch > Include Libraries > Manage Libraries. Type Adafruit SHT31 in the search bar and install the latest version.

Type Adafruit BusIO in the search bar and install it as well.

ESP32 Display BME280 and SHT31 Temperature Readings on OLED Code

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>
#include <Adafruit_SHT31.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Adafruit_BME280 bme; 
Adafruit_SHT31 sht31 = Adafruit_SHT31();

Adafruit_SSD1306 display = Adafruit_SSD1306(128, 32, &Wire);
unsigned long delayTime;

void setup() {
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);  
   // init done
  display.display();
  delay(100);
  display.clearDisplay();
  display.display();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  
  bool status;
  status = bme.begin(0x76);  
  if (!status) {
    Serial.println("Could not find a valid BME280 sensor, check wiring!");
    while (1);
  }

  if (! sht31.begin(0x44)) {   
    Serial.println("Check circuit. SHT31 not found!");
    while (1) delay(1);
  }

  Serial.println();
}


void loop() { 
  
  display.setCursor(0,0);
  
  Serial.print("Temperature BME280 = "); Serial.print(bme.readTemperature()); Serial.println(" °C");
  display.print("Temperature: "); display.print(bme.readTemperature()); display.println(" C");

  display.setCursor(0,20);
   
  Serial.print("Temperature SHT31 = "); Serial.print(sht31.readTemperature()); Serial.println(" °C");
  display.print("Temperature: "); display.print(sht31.readTemperature()); display.println(" C");

  Serial.println();
  display.display();
  display.clearDisplay();

  delay(1000);
}

How the Code Works?

Now, let us understand how each part of the code works.

The code starts with including all the necessary libraries which are needed for the proper functionality of the code. The Wire.h will allow us to communicate through the I2C protocol. The rest of the libraries are the ones that we just installed for the functionality of the BME280 sensor, SHT31 sensor and OLED.

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>
#include <Adafruit_SHT31.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Then, we define the Adafruit_BME280 object named ‘bme’ by setting it on the default I2C GPIO pins and create the Adafruit_SHT31 object called ‘sht31.’

Adafruit_BME280 bme; 
Adafruit_SHT31 sht31 = Adafruit_SHT31();

Now, we create another object named display which will be handling the OLED display. Also, define the size of the OLED display by passing arguments to the Adafruit_SSD1306() function.

Adafruit_SSD1306 display = Adafruit_SSD1306(128, 32, &Wire);

setup()

Open the serial communication at a baud rate of 115200.

Serial.begin(115200);

Initialize the OLED display by calling the begin() method on the display object.

display.begin(SSD1306_SWITCHCAPVCC, 0x3C);

Next, we will clear the OLED screen by calling clearDisplay() function. Also, we set the color of the text using setTextColor() function and pass WHITE as an argument. If we have a dark background, we will display our text in white and if we have a bright background then we will display the text in black. Also, we set the font size using setTextSize().

  display.clearDisplay();
  display.display();
  display.setTextSize(1);
  display.setTextColor(WHITE);

Then, the BME280 sensor gets initialized using and in case of failure, an error message is printed on the serial monitor. Similarly, the SHT31 sensor is initialized as well. If the sensor initialization is not a success, a relevant message will be printed on the serial monitor.

  bool status;
  status = bme.begin(0x76);  
  if (!status) {
    Serial.println("Could not find a valid BME280 sensor, check wiring!");
    while (1);
  }

  if (! sht31.begin(0x44)) {   
    Serial.println("Check circuit. SHT31 not found!");
    while (1) delay(1);
  }

loop()

Inside the loop() function, we acquire the BME280 and SHT31 temperature readings using bme.readTemperature() and sht31.readTemperature respectively. These are then displayed in the Arduino serial monitor and the OLED after every second.


void loop() { 
  
  display.setCursor(0,0);
  
  Serial.print("Temperature BME280 = "); Serial.print(bme.readTemperature()); Serial.println(" °C");
  display.print("Temperature: "); display.print(bme.readTemperature()); display.println(" C");

  display.setCursor(0,20);
   
  Serial.print("Temperature SHT31 = "); Serial.print(sht31.readTemperature()); Serial.println(" °C");
  display.print("Temperature: "); display.print(sht31.readTemperature()); display.println(" C");

  Serial.println();
  display.display();
  display.clearDisplay();

  delay(1000);
}

Demonstration

To see the demonstration of the above code, upload the code to ESP32. But, before uploading code, make sure to select ESP32 Dev Module from Tools > Board and also select the correct COM port to which the board is connected from Tools > Port.

Once the code is successfully uploaded to the board, the OLED will start displaying the temperature readings from the two sensors as shown below:

ESP32 Multiple I2C devices with different addresses Display temperature on OLED demo

Moreover, you can also view the temperature readings in the Arduino serial terminal. Remember to set the baud rate at 115200.

ESP32 Multiple I2C devices with different addresses Display temperature terminal — Serial Monitor

Use Same Addresses Multiple I2C Devices with ESP32 using TCA9548A Multiplexer IC

In the previous section, we were able to connect three different I2C devices on the same I2C pins of ESp32. This was because the ESP32 was able to identify them due to their unique address. However, what happens when we want to connect multiple devices with Arduino for I2C communication but they have the same address? For example, two BME280 sensors connected with ESP32 or two OLEDs connected with ESP32.

To use the same I2C devices with ESP32, we would either have to change the I2C address of the device or use an I2C multiplexer. However, it is not that simple to change the address of a device and it only allows limited devices to be used on the same I2C bus. Hence we can use a multiplexer eg. TCA9548A that will allow a maximum of eight devices with the same addresses to be connected to the same I2C bus. It operates on a range of 3-5.5 volts therefore making it convenient to use with microcontrollers having 3.3/5V logic pins.

The diagram below shows the TCA9548A multiplexer that we will use with I2C devices having the same address in order to communicate with ESP32.

TCA9548A 1-to-8 I2C Multiplexer ic — TCA9548A Multiplexer

It is an electronic switching device that enables the users to connect multiple I2C busses with itself. All the slaves which have the same address need to be on connected to different busses. In order to communicate with the slave, the bus that is connected to the slave is switched by the user and then addressed.

TCA9548A Multiplexer Pinout

The diagram below shows the pinout of the TCA9548A multiplexer which acts as an I2C expander.

Vin: This is the pin that provides power to the module. Connect 3.3V or Vin pin of ESP32 with this pin.
GND: This is the pin which provides the common ground.
SDA: This is the I2C serial data pin which is connected with the master device.
SCL: This is the I2C serial clock pin which is connected with the master device.
RST: This pin is responsible for resetting the multiplexer.
A0, A1, A2: These three pins are used to change the I2C address of the multiplexer. By default, its address is 0x70 when these pins are unconnected. With the help of this module, a single I2C address can be expanded to a maximum of eight I2C addresses.
SDx, SCx: These are the external I2C channels Channel 0 to Channel 7. Connect SDA pin with SDx and SCL pin with SCx for each I2C device having same address.

ESP32 Display Text on OLEDs using TCA9548A Multiplexer

Lets show you how to connect and program two OLEDs having the same address 0x3C with ESP32 using the TCA9548A multiplexer. We will require the following components:

Components Required

ESP32 board
Two SSD1306 OLEDs
TCA9548A Multiplexer
Four 10k ohm pullup resistors
Breadboard
Connecting Wires

Interface ESP32 with TCA9548A multiplexer with OLEDs

Lets show you how to connect TCA9548A multiplexer with ESP32 and the OLEDs. The ESP32 will act as a master, and the OLEDs will act as slaves.

Follow the schematic diagram below to connect all the devices.

ESP32 with TCA9748A Multiplexer with OLEDs schematic diagram

The table below shows the pins of TCA9548A connected with ESP32 and the two OLEDs.

TCA9548A	Connections with rest of the devices
Vin	3.3V of ESP32, VCC of both OLEDs
GND	GND of ESP32, GND of both OLEDs
SDA	GPIO21 of ESP32
SCL	GPIO22 of ESP32
SD0	SDA of OLED1 with 10k ohm pullup resistor
SC0	SCL of OLED1 with 10k ohm pullup resistor
SD1	SDA of OLED2 with 10k ohm pullup resistor
SC1	SCL of OLED2 with 10k ohm pullup resistor

ESP32 with TCA9748A Multiplexer with OLEDs

ESP32 Display Text on OLEDs using TCA9548A Multiplexer Code

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Adafruit_SSD1306 display = Adafruit_SSD1306(128, 32, &Wire, -1);

void TCA9548A(uint8_t bus) //activate particular channel
{
  Wire.beginTransmission(0x70);  // TCA9548A address is 0x70
  Wire.write(1 << bus);          // send byte to select bus
  Wire.endTransmission();
}

void setup()
{
  Serial.begin(115200);
  Wire.begin();
  delay(100);

  TCA9548A(0);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(20, 10);
  display.setTextColor(WHITE);
  display.println("OLED #1");
  display.display(); 

  TCA9548A(1);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(20, 10);
  display.setTextColor(WHITE);
  display.println("OLED #2");
  display.display(); 

}

void loop() {
  
}

How the Code Works?

Now, let us understand how each part of the code works.

The code starts with including all the necessary libraries which are needed for the proper functionality of the code. The Wire.h will allow us to communicate through the I2C protocol and Adafruit_GFX.h and Adafruit_SSD1306.h are the OLED libraries.

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Now, we create an object named display which will be handling the OLED display. Also, define the size of the OLED display by passing arguments to the Adafruit_SSD1306() function.

Adafruit_SSD1306 display = Adafruit_SSD1306(128, 32, &Wire, -1);

Next we define a function for TCA9548A() that takes in a single parameter which is the I2C bus channel. This function is called whenever we want to activate a particular I2C channel.

void TCA9548A(uint8_t bus) 
{
  Wire.beginTransmission(0x70);  // TCA9548A address is 0x70
  Wire.write(1 << bus);          // send byte to select bus
  Wire.endTransmission();
}

setup()

Open the serial communication at a baud rate of 115200 and initiate the I2C communication.

  Serial.begin(115200);
  Wire.begin();

Next we activate I2C channel 0 by calling TCA9548A() function as pass 0 as a parameter inside it. Our first OLED is connected with I2C channel 0. After that we initialize the OLED display, clear the screen, set the color of the text, set the font size and the cursor position. Then we print the text ‘OLED #1’ on the display.

  TCA9548A(0);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(20, 10);
  display.setTextColor(WHITE);
  display.println("OLED #1");
  display.display();

Next we activate I2C channel 1 by calling TCA9548A() function as pass 1 as a parameter inside it. Our second OLED is connected with I2C channel 1. After that we initialize the OLED display, clear the screen, set the color of the text, set the font size and the cursor position. Then we print the text ‘OLED #2’ on the display.

TCA9548A(1);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(20, 10);
  display.setTextColor(WHITE);
  display.println("OLED #2");
  display.display();

Demonstration

Once the code is successfully uploaded to the board, the two OLEDs will start displaying their respective texts as shown below:

TCA9548A I2C Multiplexer with ESP32 Use Multiple Devices having Same and Different Addresses

ESP32 I2C Pins

Using Multiple Slave I2C Devices with ESP32 (I2C devices with different addresses)

Interface ESP32 with OLED, BME280 and SHT31

ESP32 I2C Scanner Arduino Sketch

ESP32 Display BME280 and SHT31 Temperature Readings on OLED

Installing SSD1306 OLED Library in Arduino IDE

Installing BME280 Arduino Library

Install SHT31 Arduino Library

ESP32 Display BME280 and SHT31 Temperature Readings on OLED Code

How the Code Works?

setup()

loop()

Demonstration

Use Same Addresses Multiple I2C Devices with ESP32 using TCA9548A Multiplexer IC

TCA9548A Multiplexer Pinout

ESP32 Display Text on OLEDs using TCA9548A Multiplexer

Interface ESP32 with TCA9548A multiplexer with OLEDs

ESP32 Display Text on OLEDs using TCA9548A Multiplexer Code

How the Code Works?

setup()

Demonstration

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ESP32 I2C Pins

Using Multiple Slave I2C Devices with ESP32 (I2C devices with different addresses)

Interface ESP32 with OLED, BME280 and SHT31

ESP32 I2C Scanner Arduino Sketch

ESP32 Display BME280 and SHT31 Temperature Readings on OLED

Installing SSD1306 OLED Library in Arduino IDE

Installing BME280 Arduino Library

Install SHT31 Arduino Library

ESP32 Display BME280 and SHT31 Temperature Readings on OLED Code

How the Code Works?

setup()

loop()

Demonstration

Use Same Addresses Multiple I2C Devices with ESP32 using TCA9548A Multiplexer IC

TCA9548A Multiplexer Pinout

ESP32 Display Text on OLEDs using TCA9548A Multiplexer

Interface ESP32 with TCA9548A multiplexer with OLEDs

ESP32 Display Text on OLEDs using TCA9548A Multiplexer Code

How the Code Works?

setup()

Demonstration

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