W09 — Input Devices

The schematic includes:

• A tactile SMD push button on pin D1.
• A through-hole LED on pin D9, with a current-limiting resistor to prevent overcurrent damage to both the LED and the microcontroller.

I chose a through-hole LED for ease of soldering and visual clarity, and an SMD tactile button to practice working with surface-mount components.

With the schematic complete, I moved to the PCB layout design phase in KiCad.

Key layout decisions: button placed at the board edge for easy thumb access; 0.8 mm trace widths for signal lines; ground fill on the bottom copper layer to reduce noise and simplify routing.

The firmware was written in the Arduino IDE using the ESP32-C3's Arduino-compatible environment. It polls the button state on every loop cycle and mirrors it to the LED — with structured Serial.println() logging added so each state transition is visible in the Serial Monitor for verification.

// XIAO ESP32-C3 — Button Input / LED Output with Serial logging
const int LED_PIN    = 9;   // GPIO9  → D9
const int BUTTON_PIN = 3;   // GPIO3  → D1
int lastState = HIGH;       // tracks previous button state

void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);  // pull-up: HIGH at rest, LOW when pressed
}

void loop() {
  int currentState = digitalRead(BUTTON_PIN);

  if (currentState == LOW && lastState == HIGH) {
    // Button just pressed
    Serial.println("[INPUT]  Button State: PRESSED (GPIO3 = LOW)");
    Serial.println("[ACTION] Writing HIGH to LED_PIN (GPIO9)");
    digitalWrite(LED_PIN, HIGH);
    Serial.println("[STATUS] LED --> ON");
    Serial.println("[INFO]   Holding button for 2 seconds...");
    delay(2000);
  }

  if (currentState == HIGH && lastState == LOW) {
    // Button just released
    Serial.println("[INPUT]  Button State: RELEASED (GPIO3 = HIGH)");
    Serial.println("[ACTION] Writing LOW to LED_PIN (GPIO9)");
    digitalWrite(LED_PIN, LOW);
    Serial.println("[STATUS] LED --> OFF");
    Serial.println("[INFO]   Button idle for 2 seconds...");
    delay(2000);
  }

  lastState = currentState;
}

Serial Monitor Output

Opening the Serial Monitor at 115200 baud shows the exact state transitions in real time. The output below is captured from a live button press-and-release cycle:

The timestamps confirm the button was held for exactly 1.987 seconds (17.593 → 19.580), and every transition — read, write, and status — is logged in sequence with no missed events.

After uploading the firmware, I tested the board by pressing and releasing the button repeatedly to confirm:

1. The LED illuminates immediately when the button is pressed.
2. The LED turns off cleanly when the button is released.
3. No false triggers occur when the button is not pressed.
4. Behaviour is consistent across multiple press cycles.

All four conditions were satisfied. The response felt instantaneous — confirming that the INPUT_PULLUP configuration and polling-based loop are sufficient for this interaction speed.

Demo Video

The following video demonstrates the board in operation: pressing the button illuminates the LED, releasing it turns the LED off.