LamaPLC: SHT Sensirion Temperature/humidity sensor with I²C communication

Sensirion SHT sensors are a series of highly accurate, reliable digital humidity and temperature sensors built on the company's proprietary CMOSens Technology, offering fully calibrated outputs and long-term stability for a wide range of applications.

Type of measurement	Model	Power voltage	Measurement, range, accuracy	Communication	Note
Temperature Humidity	Sensirion SHT20	3.3V (2.1 .. 3.6V)	Temperature measurement range: -40 .. +125 °C Temperature measurement accuracy: ±0.3°C Humidity measurement range: 0..100% RH Humidity measurement accuracy:±3%	I²C default addr.: 0x40/41	3.2 µW (at 8 bits, 1 measurement /s)
Temperature Humidity	Sensirion SHT21	3.3V (2.1 .. 3.6V)	Temperature measurement range: -40 .. +125 °C Temperature measurement accuracy: ±0.3°C Humidity measurement range: 0..100% RH Humidity measurement accuracy: ±2%	I²C default addr.: 0x40/41	3.2 µW (at 8 bits, 1 measurement /s)
Temperature Humidity	Sensirion SHT25	3.3V (2.1 .. 3.6V)	Temperature measurement range: -40 .. +125 °C Temperature measurement accuracy: ±0.2°C Humidity measurement range: 0..100% RH Humidity measurement accuracy: ±1.8%	I²C default addr.: 0x40/41	3.2 µW (at 8 bits, 1 measurement /s)
Temperature Humidity	Sensirion SHT30	3.3 / 5 V (2.15 .. 5.5V)	Temperature measurement range: -40 .. +125 °C Temperature measurement accuracy: ±0.2°C Humidity measurement range: 0..100% RH Humidity measurement accuracy: ±2% (10..90%)	I²C default addr.: 0x44/45	4.8 µW (1 measurement/s)
Temperature Humidity	Sensirion SHT31	3.3 / 5 V (2.15 .. 5.5V)	Temperature measurement range: -40 .. +125 °C Temperature measurement accuracy: ±0.2°C Humidity measurement range: 0..100% RH Humidity measurement accuracy: ±2% (0..100%)	I²C default addr.: 0x44/45	4.8 µW (1 measurement/s)
Temperature Humidity	Sensirion SHT35	3.3 / 5 V (2.15 .. 5.5V)	Temperature measurement range: -40 .. +125 °C Temperature measurement accuracy: ±0.2°C Humidity measurement range: 0..100% RH Humidity measurement accuracy: ±1.5% (0..80%)	I²C default addr.: 0x44/45	4.8 µW (1 measurement/s)
Temperature Humidity	Sensirion SHT40	3.3 (1.08 .. 3.6V)	Temperature measurement range: -40 .. +125 °C Temperature measurement accuracy: ±0.2°C Humidity measurement range: 0..100% RH Humidity measurement accuracy: ±1.8%	I²C default addr.: 0x44/45	4.0 µW (1 measurement/s)

The SGP sensors can be integrated with the Tasmota system. For more information, see here.

Type of measurement	Name	Pics	Sensors	Description
- Temperature - Humidity	SHTxx modul		SHT20 SHT30 SHT40	I²C interface default address: 0x44/45 wiring colors: - black: GND - red: VCC (3.3V / 5V) - white: SDA - yellow: SCL
- Temperature - Humidity	GY-21		HTU21 Si-7021 SHT21	I²C interface (only 1 modul, default address: 0x40) GY-21 is a reliable and durable module for detecting temperature and humidity values compatible with Arduino, Atmega328p, ESP and Raspberry Typical measurement accuracy temperature: +/-1°C deviation between -30°C and 90°C Typical measurement accuracy humidity: +/-2% RL between 5% and 95% RL

¹: The SHT20, HTU20, and Si7020 are different manufacturers' versions of essentially the same I²C digital humidity and temperature sensor chip, designed to be hardware- and software-compatible. The GY-20 is a generic breakout board that uses one of these chips.

²: The SHT21, HTU21, and Si7021 are very similar digital humidity and temperature sensor chips from different manufacturers (Sensirion, Measurement Specialties, and Silicon Labs, respectively), while the GY-21 is a generic breakout board that uses one of these chips. They are largely interchangeable in hardware and software for most general-purpose applications.

³: The SHT31, HTU31, and Si7031 are high-accuracy digital temperature and humidity sensor chips from different manufacturers (Sensirion, TE Connectivity, and Silicon Labs, respectively) that are designed to be largely interchangeable. The GY-31 is a generic name for a breakout board that typically uses the SHT31 chip.

Wiring

• SCL: A5
• GND: GND
• SDA: A4
• Vdd: 5V or 3.3V

Arduino code

This example uses the SHT21 library to read temperature and humidity every 2 seconds

#include <Wire.h>
#include "SHT21.h" // Install "SHT21" or "HTU21D" library via Library Manager
 
SHT21 sht;
 
void setup() {
  Wire.begin();        // Initialize I2C communication
  Serial.begin(115200); // Set baud rate for Serial Monitor
  Serial.println("GY-21 (SHT21) Sensor Test");
}
 
void loop() {
  // Read values from the sensor
  float temperature = sht.getTemperature();
  float humidity = sht.getHumidity();
 
  // Check if readings are valid
  if (!isnan(temperature) && !isnan(humidity)) {
    Serial.print("Temperature: ");
    Serial.print(temperature, 1); // Print with 1 decimal place
    Serial.print(" °C\t");
 
    Serial.print("Humidity: ");
    Serial.print(humidity, 1);
    Serial.println(" %");
  } else {
    Serial.println("Failed to read from GY-21 sensor!");
  }
 
  delay(2000); // Wait 2 seconds before the next reading
}

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