I2C Multiplexer (TCA9548A)¶

Overview¶

The TCA9548A I2C multiplexer allows multiple I2C devices with the same address to coexist on the same bus by creating 8 separate I2C channels.

I2C Multiplexer

Specifications¶

Parameter	Value
Model	TCA9548A
Channels	8 selectable I2C buses
Interface	I2C
Operating Voltage	3.3V - 5V
I2C Address	0x70 (default)
Switching	Individual channel control

Why Use a Multiplexer?¶

Common Scenarios¶

Same Address Sensors: Multiple sensors of same type (e.g., two temperature sensors with address 0x48)
Address Conflicts: Two different sensors with identical factory addresses
Bus Isolation: Separate noisy devices from sensitive ones
Debugging: Isolate devices to troubleshoot

Pinout¶

Pin	Function	ESP32 Connection
VCC	Power	3.3V or 5V
GND	Ground	GND
SDA	I2C Data (master side)	GPIO21
SCL	I2C Clock (master side)	GPIO22
SD0-SD7	Channel 0-7 Data	Connect to sensor SDA
SC0-SC7	Channel 0-7 Clock	Connect to sensor SCL

Wiring Diagram¶

TCA9548A              ESP32               Sensors
--------              -----               -------
VCC        --------->  3.3V
GND        --------->  GND
SDA        --------->  GPIO21
SCL        --------->  GPIO22
SD0/SC0    --------------------------->  Sensor 1 (Channel 0)
SD1/SC1    --------------------------->  Sensor 2 (Channel 1)
SD2/SC2    --------------------------->  Sensor 3 (Channel 2)
...                                    ...
SD7/SC7    --------------------------->  Sensor 8 (Channel 7)

Required Libraries¶

No special library required - uses standard Wire library.

Code Example¶

Basic Usage¶

#include <Wire.h>

#define MULTIPLEXER_ADDR 0x70  // TCA9548A address

// Select channel (0-7)
void selectChannel(uint8_t channel) {
  if (channel > 7) return;

  Wire.beginTransmission(MULTIPLEXER_ADDR);
  Wire.write(1 << channel);
  Wire.endTransmission();
}

// Disable all channels
void disableAllChannels() {
  Wire.beginTransmission(MULTIPLEXER_ADDR);
  Wire.write(0);
  Wire.endTransmission();
}

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

  Serial.println("TCA9548A Multiplexer Test");

  // Scan all channels
  for (uint8_t channel = 0; channel < 8; channel++) {
    selectChannel(channel);

    Serial.print("Channel ");
    Serial.print(channel);
    Serial.print(": ");

    // Scan for devices on this channel
    int deviceCount = 0;
    for (uint8_t address = 1; address < 127; address++) {
      Wire.beginTransmission(address);
      if (Wire.endTransmission() == 0) {
        Serial.print("0x");
        if (address < 16) Serial.print("0");
        Serial.print(address, HEX);
        Serial.print(" ");
        deviceCount++;
      }
    }

    if (deviceCount == 0) {
      Serial.print("No devices");
    }
    Serial.println();
  }

  disableAllChannels();
}

void loop() {
  // Example: Read from sensor on channel 0
  selectChannel(0);
  // TODO: Add sensor reading code

  // Read from sensor on channel 1
  selectChannel(1);
  // TODO: Add sensor reading code

  delay(1000);
}

With Multiple Temperature Sensors¶

#include <Wire.h>

#define MULTIPLEXER_ADDR 0x70

void selectChannel(uint8_t channel) {
  Wire.beginTransmission(MULTIPLEXER_ADDR);
  Wire.write(1 << channel);
  Wire.endTransmission();
}

float readTemperature(uint8_t channel) {
  selectChannel(channel);
  // TODO: Add actual sensor reading code
  return 25.0; // Placeholder
}

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

void loop() {
  // Read from multiple sensors with same address
  float temp1 = readTemperature(0);  // Sensor 1 on channel 0
  float temp2 = readTemperature(1);  // Sensor 2 on channel 1
  float temp3 = readTemperature(2);  // Sensor 3 on channel 2

  Serial.print("Temp 1: ");
  Serial.print(temp1);
  Serial.print("°C, Temp 2: ");
  Serial.print(temp2);
  Serial.print("°C, Temp 3: ");
  Serial.print(temp3);
  Serial.println("°C");

  delay(2000);
}

Address Configuration¶

The TCA9548A I2C address can be changed using the A0-A2 pins:

A0	A1	A2	Address
GND	GND	GND	0x70
VCC	GND	GND	0x71
GND	VCC	GND	0x72
VCC	VCC	GND	0x73
GND	GND	VCC	0x74
VCC	GND	VCC	0x75
GND	VCC	VCC	0x76
VCC	VCC	VCC	0x77

Testing¶

Verification Steps¶

Connect multiplexer and one sensor
Upload channel scanner code
Verify sensor detected on selected channel only
Test multiple sensors on different channels

Troubleshooting¶

Issue	Solution
No devices detected	Check multiplexer address, verify channel selection
All channels show same device	Device connected to main bus instead of channel
Intermittent connections	Check wiring, ensure good connections
Device not responding	Verify correct channel selected before communication

Best Practices¶

Always select channel before I2C communication
Disable channels when not in use (optional)
Keep I2C wires short (< 30cm per segment)
Use pull-up resistors (4.7kΩ) if needed

Next Steps¶

Connect multiple sensors with same address
Proceed to full integration