Documentation

// Level-shifted I2C scan from 5V Arduino to 3.3V devices
// The shifter is on SDA/SCL; your code doesn't change.

#include <Wire.h>

void setup() {
  Serial.begin(9600);
  Wire.begin();
  Serial.println("Scanning I2C bus through level shifter...");
}

void loop() {
  byte count = 0;
  for (byte addr = 1; addr < 127; addr++) {
    Wire.beginTransmission(addr);
    if (Wire.endTransmission() == 0) {
      Serial.print("Found device at 0x");
      if (addr < 16) Serial.print("0");
      Serial.println(addr, HEX);
      count++;
    }
  }
  Serial.print("Total devices: ");
  Serial.println(count);
  delay(3000);
}

// ESP32 (3.3V) driving a 5V peripheral through the level shifter.
// Toggles a 5V output via one channel.

const int logicOut = 5;  // ESP32 GPIO, shifted to 5V on the other side

void setup() {
  Serial.begin(115200);
  pinMode(logicOut, OUTPUT);
}

void loop() {
  digitalWrite(logicOut, HIGH);
  Serial.println("5V side: HIGH");
  delay(500);
  digitalWrite(logicOut, LOW);
  Serial.println("5V side: LOW");
  delay(500);
}

# Raspberry Pi I2C scan through the level shifter
# Requires: sudo raspi-config -> Interface Options -> I2C enabled
# Install: sudo apt install i2c-tools
#          pip install smbus2

from smbus2 import SMBus

bus = SMBus(1)
print("Scanning I2C bus (through level shifter)...")
found = []
for addr in range(1, 128):
    try:
        bus.read_byte(addr)
        found.append(hex(addr))
    except OSError:
        pass
print("Devices:", found if found else "none")
bus.close()

# Pico I2C scan through the level shifter (GP0 SDA, GP1 SCL)

from machine import I2C, Pin

i2c = I2C(0, sda=Pin(0), scl=Pin(1), freq=100000)
devices = i2c.scan()
print("Devices found (through shifter):", [hex(d) for d in devices])