Week 10 — Output Devices

Measuring VCC and GND on the Board

First, I measured the voltage between VCC and GND on the board. The multimeter was set to DC voltage mode. The red probe was connected to VCC, and the black probe was connected to GND.

Measuring VCC and GND of the LED Module

Then, I measured the voltage of the LED module itself. My own PCB did not have the same connector type for this LED module, so I used another compatible board for this measurement. This allowed me to connect the LED module correctly and measure the voltage between its VCC and GND pins.

This compatible board was only used for the voltage measurement because of the connector type. For the output control test, I still used my XIAO ESP32-C3 board as the microcontroller board.

Group Assignment Result

Through this measurement, I confirmed that the LED output device received a stable supply voltage. The board VCC and GND measured about 3.32V, and the LED module VCC and GND measured about 3.56V in my test setup.

This test helped me understand the basic power condition of a simple output device. Compared with the servo motor, the LED module was much easier and safer to measure because it required less current and did not cause unstable power behavior.

Components

• XIAO ESP32-C3 board
• My own XIAO ESP32-C3 PCB
• Line finder sensor
• LED module
• Servo motor
• Breadboard power module
• Breadboard
• USB cable
• Jumper wires

Wiring

The line finder sensor has both AO and DO pins. In this test, I used the DO pin as a digital input signal. The LED module was connected to another digital output pin on the XIAO ESP32-C3.

In my setup, the line finder module used two signal pins. Pin 1 was AO, and pin 2 was DO. The LED module was connected to another port, and I used D3 as the LED signal pin.

Line Finder VCC  → XIAO ESP32-C3 3.3V
Line Finder GND  → XIAO ESP32-C3 GND
Line Finder AO   → XIAO ESP32-C3 D1
Line Finder DO   → XIAO ESP32-C3 D2

LED VCC          → XIAO ESP32-C3 3.3V
LED GND          → XIAO ESP32-C3 GND
LED Signal       → XIAO ESP32-C3 D3

Arduino Code

I used the following Arduino code to read the digital output from the line finder sensor and control the LED module. In my test, the line finder output was 1 when it detected a black surface, so the LED was turned on when the digital value was 1.

const int lineFinderDO = D2;  // Line finder DO connected to D2
const int ledPin = D3;        // LED signal connected to D3

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

  pinMode(lineFinderDO, INPUT);
  pinMode(ledPin, OUTPUT);

  Serial.println("Line Finder controls LED");
}

void loop() {
  int lineValue = digitalRead(lineFinderDO);

  Serial.print("DO: ");
  Serial.println(lineValue);

  // In my test:
  // DO = 1 means black surface
  // DO = 0 means white surface
  if (lineValue == 1) {
    digitalWrite(ledPin, HIGH);  // Black surface: LED on
  } else {
    digitalWrite(ledPin, LOW);   // White surface: LED off
  }

  delay(100);
}

Testing Process

After connecting the line finder sensor and the LED module, I uploaded the Arduino code to the XIAO ESP32-C3 board. I opened the Arduino Serial Monitor to check the digital value from the line finder sensor.

In my test, when the line finder detected a black surface, the Serial Monitor showed DO = 1, and the LED turned on. When the sensor detected a white surface, the Serial Monitor showed DO = 0, and the LED turned off.

Result

The LED output test worked successfully. The XIAO ESP32-C3 read the digital signal from the line finder sensor and used this value to control the LED module. This confirmed that my board could control a physical output device through code.

This experiment also helped me understand how an input signal can be translated into an output behavior. The line finder detected the surface condition, and the LED gave a visible response.

Servo Wiring with External Power

The most important rule in this setup was common ground. The external power supply GND had to be connected to the XIAO ESP32-C3 GND. However, the external 5V should not be connected directly to the 3.3V pin of the microcontroller.

External 5V +      → Breadboard + rail
External GND -     → Breadboard - rail

Servo red wire     → Breadboard + rail
Servo black wire   → Breadboard - rail
Servo signal wire  → XIAO ESP32-C3 D1 / A1

XIAO ESP32-C3 GND  → Breadboard - rail

Servo Test Code

I used the ESP32Servo library to test the servo movement. The movement range was kept small to reduce current spikes and make the test more stable.

#include <ESP32Servo.h>

Servo myServo;

const int servoPin = D1;  // Servo signal connected to D1 / A1

void setup() {
  myServo.setPeriodHertz(50);
  myServo.attach(servoPin, 500, 2500);
}

void loop() {
  myServo.write(70);
  delay(800);

  myServo.write(110);
  delay(800);
}

Servo Test Result

This test helped me understand why motors are more difficult to power than simple LED modules. The LED module could be powered directly from the microcontroller board, but the servo motor needed a separate 5V power source to avoid voltage drops and reset problems.

Because of this, I used the LED module for the formal group measurement, and kept the servo motor as an additional output device test.