Example Setup: ESP32 3.3V | CustomTypeOne Help Center

🧰 What you need:

ESP32 board (like a DevKitC or NodeMCU-ESP32)
USB-A cable with exposed 5V (red) and GND (black) wires
Two resistors for voltage divider (e.g., 10kΩ + 20kΩ → drops 5V to ~3.3V)
Breadboard and jumper wires

🔌 Wiring

USB Wire	Connect to
Red (5V)	Voltage divider → ESP32 GPIO (e.g., GPIO 18)
Black (GND)	ESP32 GND

Voltage divider setup:

USB 5V → [20kΩ] → GPIO 18
                  ↓
                [10kΩ] → GND

This drops 5V down to ~3.3V safely.

✅ Example Code (ESP32, digital read)

const int usbPowerPin = 18;  // GPIO18 gets the divided signal
bool lastState = LOW;

void setup() {
  pinMode(usbPowerPin, INPUT);
  Serial.begin(115200);
}

void loop() {
  bool currentState = digitalRead(usbPowerPin);

  if (currentState != lastState) {
    if (currentState == HIGH) {
      Serial.println("USB Power ON");
      // YOUR ALERT START CODE GOES HERE
    } else {
      Serial.println("USB Power OFF");
      // YOUR ALERT STOP CODE GOES HERE
    }
    lastState = currentState;
  }

  delay(100); // debounce / polling delay
}

⚠️ Important:

Do NOT connect 5V directly to ESP32 pins — always drop it to ≤3.3V.
ESP32 pins are usually labeled GPIO on your board — you can pick most, but avoid strapping pins (like GPIO0, GPIO2, GPIO15).
Use Serial.begin(115200) — ESP32 typically uses higher serial baud rates than Arduino Uno.