In theory it seems 128 devices can be connected. But practically it depends on the current drawn by the devices. The signals get weak if you connect more devices. You need to try adding and let everybody know how much you reached successfully.

Depends, I have used esp32 with omron thermal array sensors which work on 5v, but the sensors accepted 3.3v data and esp32 pins seems 5v tolerant so I faced no issue. But as a precaution you must use a suitable resistor to limit current. In my case I used 1k resistor in series with scl and sda lines.
Here’s the trick with data transmission here, mostly half their vcc seems to be threshold point that is 1.65 for esp32 and 2.5v for sensor. So it kinda works fine.

But I have a major problem where I hope to get your support:
I tried to connect two HTU21D humiditiy sensors (where the address is fixed to 0x40) to an ESP32-S3 Mini Development Board.

I used your explanations in chapter “ESP32 Using Two I2C Bus Interfaces”, which is exactly what I need, and tried to modify it in a way to connect the HTU21D sensores insted of the BME.
Unfortunately I cannot compile with the Arduino IDE.

The problem seems to be in the setup() section of the code.
When I try to start the 1st sensor I get the followeing error message: “Compilation error: void value not ignored as it ought to be”

Here is my code, maybe somebody could help me:

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <SparkFunHTU21D.h>

#define SDA_1 2 // define SDA pin of 1st I2C bus
#define SCL_1 1 // define SCL pin of 1st I2C bus
#define SDA_2 4 // define SDA pin of 2nd I2C bus
#define SCL_2 3 // define SCL pin of 2nd I2C bus

TwoWire I2C_one = TwoWire(0); // create instance of 1st I2C bus
TwoWire I2C_two = TwoWire(1); // create instance of 2nd I2C bus

HTU21D HTU21_one; // create instance of 1st HTU21 sensor
HTU21D HTU21_two; // create instance of 2nd HTU21 sensor

void setup() {
Serial.begin(115200); // start serial

I2C_one.begin(SDA_1, SCL_1, 100000); // initialize 1st I2C bus
I2C_two.begin(SDA_2, SCL_2, 100000); // initialize 2nd I2C bus

bool status1 = HTU21_one.begin(I2C_one);
if (!status1) {
Serial.println(“Could not find a valid HTU21_1 sensor, check wiring!”);
while (1);
}

bool status2 = HTU21_two.begin(I2C_two);
if (!status2) {
Serial.println(“Could not find a valid HTU21_2 sensor, check wiring!”);
while (1);
}
Serial.println();
}

void loop() {
// Read from HTU21_one
Serial.print(“Temperature sensor1 = “);
Serial.print(HTU21_one.readTemperature());
Serial.println(” *C”);

Serial.print(“Humidity sensor2 = “);
Serial.print(HTU21_one.readHumidity());
Serial.println(” %”);

Serial.println(“——————–“);

// Read from HTU21_two
Serial.print(“Temperature sensor2 = “);
Serial.print(HTU21_two.getTemperature());
Serial.println(” *C”);

Serial.print(“Humidity sensor2 = “);
Serial.print(HTU21_two.getHumidity());
Serial.println(” %”);

Serial.println(“——————–“);

delay(1000);
}

#include “Seeed_BME280.h”
#include <Wire.h>
BME280 bme280;
…
bool setSDA_SCL = Wire.setPins(23,19);
bool result;
result = bme280.init();
…

That’s great.
Thanks 😀