SHT31 Arduino Tutorial: Wiring, I²C Code and Serial Monitor,Can NYFEA FHT31 replace SHT31?

1. How do you wire an SHT31 to Arduino Uno?

An SHT31 breakout needs four Arduino Uno connections: supply, ground, SDA and SCL. Use A4 for SDA and A5 for SCL on an Uno R3, but verify the actual breakout supply rating because a module may add a regulator, level shifting or pull-up resistors that a bare SHT31 does not include.

Hardware checklist

• Arduino Uno R3 and a data-capable USB cable
• SHT31 temperature-and-humidity breakout board
• Four jumper wires that match the headers fitted to the breakout
• Breadboard, if the module cannot be connected securely without one
• A computer with Arduino IDE installed

An external 9 V adapter is unnecessary for this USB-powered bench setup. Do not power the Uno from multiple sources unless the intended power arrangement has been checked.

Board-specific warning: A4 and A5 are the Uno’s I²C pins. Other Arduino boards can place SDA and SCL elsewhere. Follow the pin labels or the official pinout for the board actually being used.

2. Which Arduino library should you install for SHT31?

Use the Adafruit SHT31 library for the sketches in this guide. Install it with Arduino Library Manager when available; manual installation also works when the extracted Adafruit_SHT31 folder contains the library files directly.

1. Open Tools → Manage Libraries.
2. Search for Adafruit SHT31.
3. Install the library and its requested dependencies.
4. Restart Arduino IDE if the header cannot be found after installation.

Manual installation: extract the downloaded archive, copy its library folder into Documents/Arduino/libraries, and restart Arduino IDE. The folder should contain the library files directly; an extra nested archive folder can prevent Adafruit_SHT31.h from being found. Library Manager is preferable when available because it also resolves dependencies.

3. How do you prepare Arduino IDE?

Prepare Arduino IDE by opening a new sketch and confirming that Wire.h and Adafruit_SHT31.h compile. Enter the complete sketch before choosing the board and serial port.

4. What SHT31 Arduino code should you use?

Use an SHT31 sketch that initializes the configured I²C address and rejects failed measurements. The reference version below uses 0x44; the diagnostic version checks both 0x44 and 0x45 and prints a machine-readable status field.

English SHT31 sketch

#include <Arduino.h>
#include <Wire.h>
#include "Adafruit_SHT31.h"

Adafruit_SHT31 sht31 = Adafruit_SHT31();

void setup() {
  Serial.begin(9600);
  while (!Serial) delay(10);
  Wire.begin();
  Serial.println("SHT31 Test");
  if (!sht31.begin(0x44)) {
    Serial.println("SHT31 sensor not found. Check wiring and address.");
    while (1) delay(1);
  }
  Serial.println("SHT31 sensor found.");
}

void loop() {
  float t = sht31.readTemperature();
  float h = sht31.readHumidity();
  if (!isnan(t)) {
    Serial.print("Temperature = ");
    Serial.print(t); Serial.print(" °C");
    Serial.print("\t\t");
  } else {
    Serial.println("Failed to read temperature");
  }
  if (!isnan(h)) {
    Serial.print("Humidity = ");
    Serial.print(h); Serial.println(" %");
  } else {
    Serial.println("Failed to read humidity");
  }
  delay(1000);
}

Corrected diagnostic version for engineering bring-up

The following version uses consistent SHT31 naming, checks both standard SHT3x addresses and makes failed measurements visible.

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

Adafruit_SHT31 sht31 = Adafruit_SHT31();
uint8_t sensorAddress = 0;
unsigned long sampleNumber = 0;

bool addressAcknowledges(uint8_t address) {
  Wire.beginTransmission(address);
  return Wire.endTransmission() == 0;
}

bool beginSHT31() {
  const uint8_t candidates[] = {0x44, 0x45};
  for (uint8_t address : candidates) {
    if (addressAcknowledges(address) && sht31.begin(address)) {
      sensorAddress = address;
      return true;
    }
  }
  return false;
}

void setup() {
  Serial.begin(9600);
  Wire.begin();
  delay(20);
  Serial.println(F("sample,ms,address,temperature_c,humidity_rh,status"));
  if (!beginSHT31()) {
    Serial.println(F("0,0,none,,,not_found"));
    while (true) delay(100);
  }
}

void loop() {
  float temperatureC = sht31.readTemperature();
  float humidityRH = sht31.readHumidity();
  sampleNumber++;
  Serial.print(sampleNumber); Serial.print(',');
  Serial.print(millis()); Serial.print(F(",0x"));
  Serial.print(sensorAddress, HEX); Serial.print(',');
  if (isnan(temperatureC) || isnan(humidityRH)) {
    Serial.println(F(",,read_failed"));
  } else {
    Serial.print(temperatureC, 2); Serial.print(',');
    Serial.print(humidityRH, 2); Serial.println(F(",ok"));
  }
  delay(1000);
}

5. How do you select the Arduino board and COM port?

Select Arduino Uno and the USB serial port that belongs to the connected board. If the port is unclear, compare the port list before and after reconnecting the Uno.

6. How do you upload and confirm the sketch?

A successful SHT31 upload ends with Done uploading in Arduino IDE. That message confirms the sketch reached the selected Uno; it does not confirm that the SHT31 answered over I²C.

If uploading fails, recheck the selected port and board, use a data-capable USB cable, close any program holding the serial port, and retry. Do not change sensor wiring to solve an upload error unless it is shorting or loading the board.

7. How do you open Serial Monitor for SHT31?

Open Tools → Serial Monitor after the upload finishes. The diagnostic sketch prints a CSV header followed by records whose final field is ok, not_found or read_failed.

8. Why must Serial Monitor use 9600 baud?

Set Serial Monitor to 9600 baud because both sketches call Serial.begin(9600). Garbled text usually indicates a baud mismatch; a blank monitor can also require an Uno reset or a serial-port check.

9. How do you know whether SHT31 readings are valid?

An SHT31 reading is usable only when the current transaction returns finite temperature and relative-humidity values and the diagnostic status is ok. Reject NaN, not_found and read_failed records instead of carrying forward an older value.

sample,ms,address,temperature_c,humidity_rh,status
1,1021,0x44,24.16,48.72,ok
2,2023,0x44,24.15,48.69,ok

If the SHT31 does not appear at 0x44, check 0x45 only when the module’s address configuration supports it. An I²C scan proves address acknowledgement; it does not prove a complete measurement transaction, correct CRC handling or sensor accuracy.

A usable bring-up record should update once per second, remain free of NaN or read_failed states, and settle toward a stable value when the sensor is left undisturbed. Plausible numbers alone are insufficient: compare the temperature and RH trend with the actual environment and investigate abrupt jumps, frozen values or repeated resets.

10. Why does SHT31 humidity fall during a warm-air test?

SHT31 temperature should rise and displayed relative humidity usually falls during a gentle warm-air check. Warming the sampled air raises its moisture capacity, so RH can fall even though the sensor has not removed water vapor.

Use only mild, moving warm air from a safe distance and stop before the breakout or nearby plastics become hot. This is a qualitative response check, not a calibration, response-time or production-qualification test. A hair dryer also changes airflow and may introduce very dry or locally heated air, so its readings cannot be treated as controlled laboratory evidence.