Input Devices

For this week, I worked with input devices by integrating a temperature and humidity sensor into my system. The goal was to read environmental data from the sensor and display it in real time on an OLED screen.

I used the SHT31 sensor as the input device and an OLED display to show the temperature and humidity readings. Both devices communicate through the I2C protocol, which allows them to share the same data lines.

This project builds directly on previous weeks:

• Week 6: PCB design
• Week 8: PCB fabrication and soldering
• Week 9: Reading a sensor and displaying its data

The board used for this assignment is the custom PCB I designed and fabricated in the previous weeks. You can see the full board design here: Week 6 — PCB Design, and its fabrication and soldering here: Week 8 — Electronics Production.

The SHT31 is a digital temperature and humidity sensor that communicates using the I2C protocol. It provides accurate environmental measurements and is widely used in embedded systems.

Key characteristics

• Digital communication (I2C)
• High accuracy temperature and humidity readings
• Fast response time
• Low power consumption

In this project, both the temperature and the humidity data were read from the sensor and displayed on the screen.

An OLED display was used as the visual output for the sensor readings. OLED screens are well suited for embedded projects because they have high contrast, are easy to read, and also communicate over I2C, so they can share the same bus as the SHT31 sensor.

The display continuously shows two values:

• Temperature, in degrees Celsius
• Humidity, in percentage (% RH)

Because the sensor and the display use different I2C addresses, both devices can operate on the same SDA and SCL lines without conflict.

Both the sensor and the display were connected to the same PCB fabricated in Week 8, sharing the I2C interface.

Since both devices use I2C, the SDA and SCL lines are shared between the sensor and the display.

The system continuously reads temperature and humidity data from the SHT31 sensor over I2C, and then updates the OLED display with the new values.

The cycle is simple and repeats continuously:

• Request a measurement from the SHT31
• Read the temperature and humidity values
• Convert the raw data into Celsius and % RH
• Print both values on the OLED screen

This is a basic example of reading an input device and presenting its data through a display.

Installing the Libraries in the Arduino IDE

To read the SHT31 temperature/humidity sensor and drive the OLED display, I did not write the low-level I2C communication from scratch — I used ready-made libraries and installed them directly from the Arduino IDE Library Manager. This is the fastest and safest way to add a library, because the IDE downloads the correct version and its dependencies for you.

Step 1 — Open the Library Manager

In the Arduino IDE I opened the Library Manager from Sketch → Include Library → Manage Libraries… (or the books icon in the left sidebar). This opens a search panel connected to the online library index.

Step 2 — Install the SHT31 sensor library

I searched for "SHT31" and installed the Adafruit SHT31 library. When it asked to also install its dependencies (the Adafruit Unified Sensor / BusIO helpers), I accepted, so everything the sensor library needs is installed together.

Step 3 — Install the OLED display library

Then I searched for "SSD1306" and installed the Adafruit SSD1306 library, accepting the Adafruit GFX dependency that it uses to draw text and graphics on the screen.

Step 4 — Include the libraries in the sketch

Once installed, the libraries are available to include at the top of the sketch with #include. From that point I could create the sensor and display objects and use their functions directly (exactly the includes used in the code below):

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_SHT31.h>

Installing the libraries through the Library Manager (instead of downloading ZIP files manually) means the IDE keeps them updated and resolves the dependencies automatically, which avoids the typical "library not found" or missing-dependency compile errors.

The code reads temperature and humidity via I2C from the SHT31 and displays both values on the OLED screen. The comments inside explain what each part does.

// ===== Libraries =====
#include <Wire.h>              // I2C communication (SDA/SCL)
#include <Adafruit_GFX.h>      // Base graphics library for the display
#include <Adafruit_SSD1306.h>  // Driver for the SSD1306 OLED
#include <Adafruit_SHT31.h>    // Driver for the SHT31 sensor

// ===== Display settings =====
#define SCREEN_WIDTH 128        // OLED width in pixels
#define SCREEN_HEIGHT 64        // OLED height in pixels
#define OLED_RESET -1           // No dedicated reset pin (shares the board reset)

// Create the display object on the I2C bus (Wire)
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// Create the sensor object
Adafruit_SHT31 sht31 = Adafruit_SHT31();

void setup() {
  Wire.begin();                          // Start the I2C bus

  display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // Init OLED at I2C address 0x3C
  display.clearDisplay();                // Clear anything on screen

  sht31.begin(0x44);                     // Init SHT31 at I2C address 0x44
}

void loop() {
  float t = sht31.readTemperature();     // Read temperature in °C
  float h = sht31.readHumidity();        // Read relative humidity in %

  display.clearDisplay();                // Wipe the previous frame
  display.setTextColor(SSD1306_WHITE);   // White text

  // --- Title ---
  display.setTextSize(1);                // Small font
  display.setCursor(0, 0);               // Top-left corner
  display.println("Sensor SHT31");

  // --- Temperature ---
  display.setTextSize(2);                // Larger font for the value
  display.setCursor(0, 20);              // Move down
  display.print(t, 1);                   // Print temperature, 1 decimal
  display.println(" C");

  // --- Humidity ---
  display.setCursor(0, 45);              // Move further down
  display.print(h, 1);                   // Print humidity, 1 decimal
  display.println(" %");

  display.display();                     // Push the buffer to the screen

  delay(1000);                           // Wait 1 second before repeating
}

Libraries

The code uses Wire.h for I2C communication, Adafruit_SHT31.h to read the sensor, and Adafruit_GFX.h with Adafruit_SSD1306.h to control the OLED display.

Initialization

In setup(), the I2C bus is started, the OLED is initialized at address 0x3C, and the SHT31 sensor is initialized at address 0x44.

Reading the Sensor

In the loop, sht31.readTemperature() and sht31.readHumidity() return the temperature in Celsius and the relative humidity in percentage.

Displaying the Data

The values are printed on the OLED using different text sizes and positions, and display.display() updates the screen. The cycle repeats every second.

The final system successfully reads temperature and humidity from the sensor and shows both values in real time on the OLED display.

• Stable readings from the sensor
• Temperature shown in °C
• Humidity shown in % RH
• Display updated every second