Input Devices

For this week, I worked with input devices by integrating a temperature sensor into my system. The goal was to read environmental temperature and use that data to control an output device automatically.

I used the SHT31 temperature sensor as the input device and programmed the system so that when the temperature reaches 30°C, a fan is activated.

This project builds directly on previous weeks:

• Week 6: PCB design
• Week 8: PCB fabrication and soldering
• Week 9: Functional integration (sensor + control)

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 readings
• Fast response time
• Low power consumption

In this project, only the temperature data was used to trigger the fan.

The sensor was connected to the same PCB fabricated in Week 8. The communication was done through the I2C interface.

The fan cannot be powered directly from the microcontroller, so it is controlled through a transistor or driver circuit.

The system continuously reads temperature data from the SHT31 sensor. Based on this reading, a decision is made:

• If temperature is below 30°C → fan OFF
• If temperature is 30°C or higher → fan ON

This type of system is an example of a basic control loop using an input device.

The code reads the temperature via I2C and controls a digital output connected to the fan.

#include "pico/stdlib.h"
#include "hardware/i2c.h"

#define I2C_PORT i2c0
#define SDA_PIN 4
#define SCL_PIN 5

#define FAN_PIN 15

#define SHT31_ADDR 0x44

void read_temperature(float *temperature) {
    uint8_t cmd[2] = {0x24, 0x00};
    i2c_write_blocking(I2C_PORT, SHT31_ADDR, cmd, 2, false);

    sleep_ms(15);

    uint8_t data[6];
    i2c_read_blocking(I2C_PORT, SHT31_ADDR, data, 6, false);

    uint16_t rawTemp = (data[0] << 8) | data[1];

    *temperature = -45 + (175 * ((float)rawTemp / 65535.0));
}

int main() {

    stdio_init_all();

    i2c_init(I2C_PORT, 100000);
    gpio_set_function(SDA_PIN, GPIO_FUNC_I2C);
    gpio_set_function(SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(SDA_PIN);
    gpio_pull_up(SCL_PIN);

    gpio_init(FAN_PIN);
    gpio_set_dir(FAN_PIN, GPIO_OUT);

    float temperature;

    while (true) {
        read_temperature(&temperature);

        if (temperature >= 30.0) {
            gpio_put(FAN_PIN, 1);
        } else {
            gpio_put(FAN_PIN, 0);
        }

        sleep_ms(1000);
    }
}

I2C Communication

The sensor is accessed through I2C using SDA and SCL pins. The command 0x2400 triggers a temperature measurement.

Temperature Conversion

The raw sensor data is converted into Celsius using the formula:

T = -45 + 175 * (raw / 65535)

Control Logic

The program compares the measured temperature with the threshold (30°C). If the condition is met, the fan is activated.

Loop Execution

The system runs continuously, updating every second.

The final system successfully reads temperature data and controls the fan automatically.

• Stable readings from the sensor
• Immediate response at 30°C
• Reliable switching of the fan