Example Code for Arduino-Temperature & Humidity Alarm
Last revision 2025/12/18
Set the temperature and humidity threshold. The pin INT generates an alarm signal when exceeding the threshold. Experimental phenomenon: The user can customize the temperature and humidity thresholds, and the ALERT pin generates an alarm signal once the values exceed the user-defined threshold.
Hardware Preparation
- DFRduino UNO R3 (or similar) x 1
- Gravity: SHT31-F Digital Temperature and Humidity Sensor x1
- Connectors
- Connect the sensor's INT pin to the main board's interrupt pin (e.g., UNO pin 2, Mega2560 pin 2, micro:bit P0).
Software Preparation
- Arduino IDE
- Download and install the SHT3x Library and Example Programs. (About how to install the library?)
Wiring Diagram
- Connect the sensor's INT pin to the main board's interrupt pin (refer to the code for pin correspondence):
- UNO/Mini/Nano: Pin 2 (Interrupt 0)
- Mega2560: Pin 2 (Interrupt 0)
- Leonardo: Pin 3 (Interrupt 0)
- micro:bit: P0
- ESP32 (mPython): P16
The ALERT pin on the sensor should be connected to the interrupt pin on the main panel when using this function.
Other Preparation Work
- Confirm the hardware IIC address matches the program's default address (0x45).
- Initialize the chip and check for successful communication.
- Set temperature and humidity thresholds (e.g., 35°C high set, 18°C low set for temperature; 70%RH high set, 19%RH low set for humidity).
- Clear the status register to ensure the ALERT pin works properly.
Sample Code
/*!
* @file alert.ino
* @brief Temperature and humidity over-threshold alarm.
* @n Experimental phenomenon: The user can customize the temperature and humidity thresholds,
* and the ALERT pin generates an alarm signal once the values exceed the user-defined threshold.
* @n NOTE: The ALERT pin on the sensor should be connected to the interrupt pin on the main panel when using this function.
* @copyright Copyright (c) 2010 DFRobot Co.Ltd (https://www.dfrobot.com)
* @licence The MIT License (MIT)
* @author [fengli]([email protected])
* @version V1.0
* @date 2019-08-26
* @get from https://www.dfrobot.com
* @url https://github.com/DFRobot/DFRobot_SHT3x
*/
#include <DFRobot_SHT3x.h>
/*!
* @brief Construct the function
* @param pWire IIC bus pointer object and construction device, can both pass or not pass parameters, Wire in default.
* @param address Chip IIC address, two optional addresses 0x44 and 0x45(0x45 in default).
* @param RST Chip reset pin, 4 in default.
* @n IIC address is determined by the pin addr on the chip.
* @n When the ADR is connected to VDD, the chip IIC address is 0x45.
* @n When the ADR is connected to GND, the chip IIC address is 0x44.
*/
//DFRobot_SHT3x sht3x(&Wire,/*address=*/0x45,/*RST=*/4);
DFRobot_SHT3x sht3x;
//The non-alarm status of the alert pin is low;
volatile int alertState = 0;
void alert(){
alertState = 1 - alertState;
}
void setup() {
Serial.begin(9600);
#ifdef ARDUINO_ARCH_MPYTHON
/* The Correspondence Table of ESP32 Interrupt Pins And Terminal Numbers
* -----------------------------------------------------------------------------------------------------
* | | DigitalPin | P0-P20 can be used as an external interrupt |
* | esp32 |--------------------------------------------------------------------------------------|
* | | Interrupt No | DigitalPinToInterrupt (Pn) can be used to query the interrupt number |
* |---------------------------------------------------------------------------------------------------|
*/
attachInterrupt(digitalPinToInterrupt(P16)/*Query the interrupt number of the P16 pin*/,alert,CHANGE);
//Open esp32's P16 pin for external interrupt, bilateral edge trigger, ALERT connected to P16
#else
/* The Correspondence Table of AVR Series Arduino Interrupt Pins And Terminal Numbers
* ---------------------------------------------------------------------------------------
* | | DigitalPin | 2 | 3 | |
* | Uno, Nano, Mini, other 328-based |--------------------------------------------|
* | | Interrupt No | 0 | 1 | |
* |-------------------------------------------------------------------------------------|
* | | Pin | 2 | 3 | 21 | 20 | 19 | 18 |
* | Mega2560 |--------------------------------------------|
* | | Interrupt No | 0 | 1 | 2 | 3 | 4 | 5 |
* |-------------------------------------------------------------------------------------|
* | | Pin | 3 | 2 | 0 | 1 | 7 | |
* | Leonardo, other 32u4-based |--------------------------------------------|
* | | Interrupt No | 0 | 1 | 2 | 3 | 4 | |
* |--------------------------------------------------------------------------------------
*/
/* The Correspondence Table of micro:bit Interrupt Pins And Terminal Numbers
* ---------------------------------------------------------------------------------------------------------------------------------------------
* | micro:bit | DigitalPin |P0-P20 can be used as an external interrupt |
* | (When using as an external interrupt, |---------------------------------------------------------------------------------------------|
* |no need to set it to input mode with pinMode)|Interrupt No|Interrupt number is a pin digital value, such as P0 interrupt number 0, P1 is 1 |
* |-------------------------------------------------------------------------------------------------------------------------------------------|
*/
attachInterrupt(/*Interrupt No*/0,alert,CHANGE);//Open the external interrupt 0, connect ALERT to the digital pin of the main control:
//UNO(2), Mega2560(2), Leonardo(3), microbit(P0).
#endif
//Initialize the chip to detect if it can communicate properly
while (sht3x.begin() != 0) {
Serial.println("The initialization of the chip is failed, please confirm whether the chip connection is correct");
delay(1000);
}
/**
* readSerialNumber Read the serial number of the chip
* @return Return 32-digit serial number
*/
Serial.print("The chip serial number");
Serial.println(sht3x.readSerialNumber());
/**
* softReset Send command resets via iiC, enter the chip's default mode single-measure mode, turn off the heater,
* and clear the alert of the ALERT pin.
* @return Read the status register to determine whether the command was executed successfully, and returning true indicates success.
*/
if(!sht3x.softReset()){
Serial.println("Failed to reset the chip");
}
/**
* @brief All flags (Bit 15, 11, 10, 4) in the status register can be cleared (set to zero).
* @n ALERT can work properly only when the bit:15 is set to 0, otherwise it will remain high.
*/
sht3x.clearStatusRegister();
/**
* startPeriodicMode Enter cycle measurement mode and set repeatability, read frequency, and only in this mode ALERT can work.
* @param measureFreq Read the data frequency, data type eMeasureFrequency_t
* @note Selectable parameters:
eMeasureFreq_Hz5, /**the chip collects data in every 2s
eMeasureFreq_1Hz, /**the chip collects data in every 1s
eMeasureFreq_2Hz, /**the chip collects data in every 0.5s
eMeasureFreq_4Hz, /**the chip collects data in every 0.25s
eMeasureFreq_10Hz /**the chip collects data in every 0.1s
* @param repeatability Read the repeatability of temperature and humidity data, the default parameter is eRepeatability_High.
* @note Optional parameters:
eRepeatability_High /**In high repeatability mode, the humidity repeatability is 0.10%RH, the temperature repeatability is 0.06°C
eRepeatability_Medium,/**In medium repeatability mode, the humidity repeatability is 0.15%RH, the temperature repeatability is 0.12°C.
eRepeatability_Low, /**In low repeatability mode, the humidity repeatability is0.25%RH, the temperature repeatability is 0.24°C
* @return Read the status of the register to determine whether the command was executed successfully, and return true indicates success.
*/
if(!sht3x.startPeriodicMode(sht3x.eMeasureFreq_10Hz)){
Serial.println("Failed to enter the periodic mode");
}
/**
* setTemperatureLimitC Set the threshold temperature and alarm clear temperature(°C)
* setTemperatureLimitF Set the threshold temperature and alarm clear temperature(°F)
* @param highset High temperature alarm point, when the temperature is greater than this value, the ALERT pin generates an alarm signal.
* @param highClear High temperature alarm clear point, alarming when the temp higher than the highset, otherwise the alarm signal will be cleared.
* @param lowset Low temperature alarm point, when the temperature is lower than this value, the ALERT pin generates an alarm signal.
* @param lowclear Low temperature alarm clear point, alarming when the temp lower than the highset, otherwise the alarm signal will be cleared.
* @note The filled value should be an integer (range: -40 to 125 degrees Celsius), -40 to 257 (Fahrenheit)highset>highClear>lowclear>lowset)
*/
//sht3x.setTemperatureLimitF(/*highset=*/35,/*highClear=*/34,/*lowSet=*/18,/*lowClear=*/20)
if(sht3x.setTemperatureLimitC(/*highset=*/35,/*highClear=*/34,/*lowSet=*/18,/*lowClear=*/20) != 0){
Serial.println("Failed to set the temperature limit");
}
/**
* setHumidityLimitRH Set the relative humidity threshold temperature and the alarm clear humidity(%RH)
* @param highset High humidity alarm point, when the humidity is greater than this value, the ALERT pin generates an alarm signal.
* @param highClear High humidity alarm clear point, alarming when the humidity higher than the highset, otherwise the alarm signal will be cleared.
* @param lowset Low humidity alarm point, when the humidity is lower than this value, the ALERT pin generates an alarm signal.
* @param lowclear Low humidity alarm clear point, alarming when the humidity lower than the highset, otherwise the alarm signal will be cleared.
* @note The filled value should be an integer (range: 0 - 100 %RH,highset>highClear>lowclear>lowset)
*/
if(sht3x.setHumidityLimitRH(/*highset=*/70,/*highClear=*/68,/*lowSet=*/19,/*lowClear=*/20) != 0){
Serial.println("Failed to set the humidity limit");
}
//Serial.println(F("string") Save stings to flash to save the dynamic ram when compiling.
Serial.println(F("----------------------Alarm Detection-------------------------------"));
Serial.println(F("Alarms raised when temp and humidity are out of the threshold range. Please connect ALERT to the main control board interrupt pin"));
Serial.println(F("-Different main contorl UNO(2), Mega2560(2), Leonardo(3), microbit(P0), mPython(P16)----"));
Serial.println(F("----------------------the humidity limit(%RH)-----------------------------------"));
/**
* @brief Measure relative humidity threshold temperature and alarm clear humidity
* @return Return true indicates successful data acquisition
*/
if(sht3x.measureHumidityLimitRH()){
Serial.print("high set:");
//getHumidityHighSetRH() Get the high humidity alarm point
Serial.print(sht3x.getHumidityHighSetRH());
Serial.print(" low clear:");
//getHumidityHighClearRH() Get the high humidity alarm clear point
Serial.println(sht3x.getHumidityLowClearRH());
Serial.print("high clear:");
//getHumidityLowClearRH() Get the low humidity alarm clear point
Serial.print(sht3x.getHumidityHighClearRH());
Serial.print(" low set:");
//getHumidityLowSetRH() Get the low humidity alarm point
Serial.println(sht3x.getHumidityLowSetRH());
} else {
Serial.println("Failed to get the humidity limit");
}
/**
* measureTemperatureLimitC Measure the threshold temperature and alarm clear temperature(°C)
* measureTemperatureLimitF Measure the threshold temperature and alarm clear temperature(°F)
* @return Return true indicates successful data acquisition
*/
Serial.println("----------------------temperature limit(°C)---------------------------------");
//Serial.println(F("----------------------temperature limit(°F)---------------------------------"));
if(sht3x.measureTemperatureLimitC()){
Serial.print("high set:");
//getTemperatureHighSetC() Get high temperature alarm points(°C)
//getTemperatureHighSetF() Get high temperature alarm points(°F)
Serial.print(sht3x.getTemperatureHighSetC());
Serial.print(" low clear:");
//getTemperatureHighClearC() Get high temperature alarm clear points(°C)
//getTemperatureHighClearF() Get high temperature alarm clear points(°F))
Serial.println(sht3x.getTemperatureLowClearC());
Serial.print("high clear:");
//getTemperatureLowClearC() Get low temperature alarm clear points(°C)
//getTemperatureLowClearF() Get low temperature alarm clear points(°F)
Serial.print(sht3x.getTemperatureHighClearC());
Serial.print(" low set:");
//getTemperatureLowSetC() Get low temperature alarm points(°C)
//getTemperatureLowSetF() Get low temperature alarm points(°F)
Serial.println(sht3x.getTemperatureLowSetC());
Serial.println("------------------------------------------------------------------");
} else {
Serial.println("Failed to get temperature limit");
}
/**
* readAlertState Read the status of the ALERT pin.
* @return High returns 1, low returns 0.
*/
//To initialize the state of ALERT
if(sht3x.readAlertState() == 1){
alertState = 1;
} else {
alertState = 0;
}
}
void loop() {
Serial.print("environment temperature(°C/F):");
/**
* getTemperatureC Get the measured temperature (in degrees Celsius)
* @return Return temperature data of the type float
*/
Serial.print(sht3x.getTemperatureC());
Serial.print(" C/");
/**
* getTemperatureF Get the measured temperature (in degrees Celsius)
* @return Return temperature data of the type float
*/
Serial.print(sht3x.getTemperatureF());
Serial.print(" F ");
Serial.print("relative humidity(%RH):");
/**
* getHumidityRH Get measured humidity (in %RH)
* @return Return humidity data of the type float
*/
Serial.print(sht3x.getHumidityRH());
Serial.println(" %RH");
//The read data frequency should greater than the frequency to collect data, otherwise the return data will make errors.
if(alertState == 1){
/**
* @brief Determine if the temperature and humidity are out of the threshold range
* @return Return the status code, representing as follows
* @n 01 Indicates that the humidity exceeds the lower threshold range
* @n 10 Indicates that the temperature exceeds the lower threshold range
* @n 11 Indicates that both the humidity and the temperature exceed the lower threshold range
* @n 02 Indicates that the humidity exceeds the upper threshold range
* @n 20 Indicates that the temperature exceeds the upper threshold range
* @n 22 Indicates that both the humidity and the temperature exceed the upper threshold range
* @n 12 Indicates that the temperature exceeds the lower threshold range,
//and the humidity exceeds the upper threshold range
* @n 21 Indicates that the temperature exceeds the upper threshold range,
//and the humidity exceeds the lower threshold range
* @n 0 Back to normal, but the alarm is not cleared.
*/
uint8_t state = sht3x.environmentState();
//Serial.println(F("string") Save stings to flash to save the dynamic ram when compiling.
if(state == 1) Serial.println(F("The humidity exceeds the lower threshold range!"));
else if(state == 10) Serial.println(F("The temperature exceeds the lower threshold range!"));
else if(state == 11) Serial.println(F("The humidity and the temperature exceed the lower threshold range!"));
else if(state == 2) Serial.println(F("The humidity exceeds the upper threshold range!"));
else if(state == 20) Serial.println(F("The temperature exceeds the upper threshold range!"));
else if(state == 22) Serial.println(F("The humidity and the temperature exceed the upper threshold range!"));
else if(state == 12) Serial.println(F("The temperature exceeds the lower threshold range,the humidity exceeds the upper threshold range!"));
else if(state == 21) Serial.println(F("The temperature exceeds the upper threshold range, and the humidity exceeds the lower threshold range!"));
else Serial.println(F("T&H back to normal, but the alarm is not cleared!"));
} else {
Serial.println(F("T&H in normal range, alarm cleared"));
}
delay(1000);
}
Result
Additional Information
- The ALERT pin only works in periodic measurement mode.
- The status code returned by
environmentState()indicates the type of threshold violation (e.g., 20 = temperature exceeds upper threshold).
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