Week 09 — Input Devices

Wiring

I connected the HC-SR04 sensor to my own XIAO ESP32S3 PCB. The sensor was powered by 5V and GND. The Trig pin was connected to D2, and the Echo pin was connected to D3.

Arduino code

I wrote the following Arduino code to trigger the ultrasonic pulse, read the Echo pulse duration, and convert it into distance in centimeters.

const int trigPin = D2;
const int echoPin = D3;

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

  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  long duration = pulseIn(echoPin, HIGH, 30000);

  float distance = duration * 0.0343 / 2;

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  delay(500);
}

Testing process

After uploading the code, I opened the Arduino Serial Monitor and set the baud rate to 115200. The sensor started printing distance values in centimeters.

I tested the sensor by moving my hand closer to and farther away from the front of the sensor. When there was no object close to the sensor, the measured distance was around 390 cm. When I moved my hand closer, the value decreased to around 8 cm, 6 cm, and 5 cm.

Result

The HC-SR04 sensor worked successfully with my XIAO ESP32S3 PCB. The distance value changed according to the position of my hand. When my hand moved closer to the sensor, the measured distance became smaller. When my hand moved farther away, the value became larger.

This confirmed that my board successfully read input data from the ultrasonic distance sensor.

Digital input test: Button module

For the digital input test, I used a button module. The module has three pins: GND, VCC, and OUT. Since the OUT pin changes between two states, HIGH and LOW, it can be used as a digital input device.

I connected the button module to my PCB. VCC was connected to 3.3V, GND was connected to GND, and OUT was connected to a digital input pin on the board.

Button Arduino code

I used the following code to read the button value and print it in the Serial Monitor.

const int buttonPin = D3;

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

void loop() {
  int buttonValue = digitalRead(buttonPin);
  Serial.println(buttonValue);
  delay(100);
}

Serial Monitor test

After uploading the code, I opened the Arduino Serial Monitor. When the button was pressed and released, the value changed between 0 and 1. This showed that the microcontroller could successfully read the button state.

Multimeter test

To check the physical voltage level of the signal, I measured the voltage between OUT and GND using a multimeter. The multimeter was set to DC voltage mode. The black probe was connected to GND, and the red probe was connected to OUT.

In one measured state, the OUT pin was about 3.29V, which represents a HIGH signal. In another measured state, the voltage was around 2.2V in my test setup. This value was not close to 0V because the measurement connection included a 2.2kΩ resistor in the circuit. Instead of assuming an ideal 0V reading, I recorded the actual voltage under my test condition.

At the same time, the Arduino Serial Monitor showed that the microcontroller could distinguish the two button states as 0 and 1. This means the button module worked as a digital input device, while the multimeter helped me observe the physical voltage level of the signal.

Through this test, I understood that the Serial Monitor shows the value interpreted by the microcontroller, while the multimeter shows the physical voltage level of the signal under the actual circuit condition.

Analog input test: Line finder sensor

To test an analog input, I used a line finder sensor. A line finder sensor detects the difference between light and dark surfaces using reflected infrared light. This module has both DO and AO pins. DO is a digital output, while AO is an analog output.

I connected the AO pin to an analog input pin on the XIAO ESP32S3 board, and I also connected the DO pin to a digital input pin. In the Serial Monitor, the DO value stayed at 1 during my test, while the AO value changed continuously when I moved the sensor over different surfaces.

In my test, the AO value changed between values such as 2652, 3367, 3633, 3978, and 4069. These values are not simply 0 or 1, so they show that the AO pin provides an analog signal related to the reflected infrared light.

Line finder Arduino code

I used the following code to read both the digital output and the analog output of the line finder sensor.

const int lineDigitalPin = D3;
const int lineAnalogPin = A0;

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

void loop() {
  int digitalValue = digitalRead(lineDigitalPin);
  int analogValue = analogRead(lineAnalogPin);

  Serial.print("DO: ");
  Serial.print(digitalValue);
  Serial.print("   AO: ");
  Serial.println(analogValue);

  delay(200);
}

Group assignment result

In the group assignment, I tested both digital and analog input signals. The button module showed a digital signal because the Serial Monitor value changed between 0 and 1. The line finder sensor showed an analog signal because its AO value changed continuously according to the surface and reflection condition.

These tests helped me understand the difference between digital input and analog input. Digital input is useful for simple state detection, while analog input can describe gradual changes in the physical environment.