How to Use SHT40: Examples, Pinouts, and Specs

The SHT40 is a digital humidity and temperature sensor designed for high accuracy and low power consumption. It is part of Sensirion's 4th generation of humidity sensors, offering improved performance in a compact form factor. The SHT40 communicates via an I²C interface, making it easy to integrate into a wide range of applications. Its small size and robust design make it ideal for use in HVAC systems, weather monitoring stations, IoT devices, and industrial automation.

• HVAC (Heating, Ventilation, and Air Conditioning) systems
• Weather stations and environmental monitoring
• IoT (Internet of Things) devices
• Smart home automation
• Industrial process control
• Consumer electronics (e.g., smart thermostats)

The SHT40 is a high-performance sensor with the following key specifications:

The SHT40 has four pins, as described in the table below:

1. Power Supply: Connect the VDD pin to a power source (1.08 V to 3.6 V) and the GND pin to ground.
2. I²C Communication: Connect the SDA and SCL pins to the corresponding I²C data and clock lines of your microcontroller. Use pull-up resistors (typically 4.7 kΩ) on both SDA and SCL lines.
3. Bypass Capacitor: Place a 100 nF capacitor close to the VDD and GND pins to stabilize the power supply.
4. Address Selection: The default I²C address is 0x44. If using multiple SHT40 sensors, configure the alternate address (0x45) as per the datasheet.

• Avoid exposing the sensor to extreme conditions (e.g., high humidity or temperature) for prolonged periods.
• Ensure proper PCB layout to minimize noise on the I²C lines.
• Use a protective cover or filter to shield the sensor from dust and contaminants in harsh environments.
• Calibrate the sensor if required for critical applications.

Below is an example of how to interface the SHT40 with an Arduino UNO using the I²C protocol. This code uses the Adafruit SHT4x library.

#include <Wire.h>
#include "Adafruit_SHT4x.h"

// Create an instance of the SHT4x sensor
Adafruit_SHT4x sht4 = Adafruit_SHT4x();

void setup() {
  Serial.begin(9600); // Initialize serial communication
  while (!Serial) delay(10); // Wait for the serial monitor to open

  // Initialize the SHT40 sensor
  if (!sht4.begin()) {
    Serial.println("Failed to find SHT40 sensor!");
    while (1) delay(10); // Halt if sensor initialization fails
  }
  Serial.println("SHT40 sensor initialized!");

  // Set the precision mode (optional)
  sht4.setPrecision(SHT4X_HIGH_PRECISION);
  Serial.println("High precision mode set.");
}

void loop() {
  sensors_event_t humidity, temp;

  // Perform a measurement
  if (!sht4.getEvent(&humidity, &temp)) {
    Serial.println("Failed to read data from SHT40!");
    return;
  }

  // Print temperature and humidity readings
  Serial.print("Temperature: ");
  Serial.print(temp.temperature);
  Serial.println(" °C");

  Serial.print("Humidity: ");
  Serial.print(humidity.relative_humidity);
  Serial.println(" %");

  delay(1000); // Wait 1 second before the next reading
}

1. Sensor Not Detected on I²C Bus:

   • Ensure the SDA and SCL lines are correctly connected to the microcontroller.
   • Verify that pull-up resistors (4.7 kΩ) are present on the I²C lines.
   • Check the sensor's power supply voltage (1.08 V to 3.6 V).

2. Incorrect Readings:

   • Ensure the sensor is not exposed to condensation or contaminants.
   • Verify that the sensor is operating within its specified temperature and humidity range.
   • Check for noise or interference on the I²C lines.

3. Arduino Code Fails to Compile:

   • Ensure the Adafruit SHT4x library is installed in the Arduino IDE.
   • Verify that the correct board and port are selected in the Arduino IDE.

Q: Can I use the SHT40 with a 5V microcontroller?
A: Yes, but you must use a level shifter to step down the I²C voltage levels to the sensor's operating range (1.08 V to 3.6 V).

Q: How do I protect the sensor in harsh environments?
A: Use a protective filter or housing to shield the sensor from dust, water, and contaminants.

Q: What is the typical response time of the SHT40?
A: The typical response time is 8 seconds for humidity and 2 seconds for temperature, depending on airflow and environmental conditions.