SHT21

Table of Contents

    Note

    This page has been moved to the Components section of the website. Please see http://developer.mbed.org/components/SHT21-temperature-and-humidity-sensor/ .

    The SHT21 is an I2C temperature and humidity sensor from Sensirion. The SHT21 digital humidity and temperature sensor is fully calibrated and offers high precision and excellent long-term stability at low cost. The digital CMOSens Technology integrates two sensors and readout circuitry on one single chip.

    SHT21 Datasheet

    SHT2x
    Misenso SHT2x Breakout Board

    The Misenso SHT2x breakout board already includes the two I2C pullups (seen above) needed.

    Wiring

    mbedSHT21 sensor
    gndgnd
    Vout(3.3V)VCC
    P9(sda)SDA
    p10(scl)SCL

    Here is a demo program using the SHT2x library that prints out the temperature and humidity

    Import programsht21_test

    Basic test program for the SHT2x library

    Last commit 23 Apr 2011 by Serge Sozonoff



    
#include "mbed.h"
#include "SHT2x.h"

SHT2x sht21(p9, p10);

DigitalOut myled(LED2);
Serial pc(USBTX, USBRX);

int rh, temp;
int error;
float relHumidity, temperature;
int userRegister;

int main() {
    sht21.SHT2x_SoftReset();
    
    error |= sht21.SHT2x_ReadUserRegister(&userRegister);  //get actual user reg
    userRegister = (userRegister & ~SHT2x_RES_MASK) | SHT2x_RES_12_14BIT;
    error |= sht21.SHT2x_WriteUserRegister(&userRegister); //write changed user reg    
    
    while (1) {
        myled = 1;
        
        pc.printf("program start\r\n");
        error |= sht21.SHT2x_MeasureHM(HUMIDITY, &rh);
        error |= sht21.SHT2x_MeasureHM(TEMP, &temp);
        
        if (error > 0)
            pc.printf("error code %d \r\n", error);

        relHumidity = sht21.SHT2x_CalcRH(rh);
        temperature = sht21.SHT2x_CalcTemperatureC(temp);
        
        pc.printf("RH value -> %f \r\n", relHumidity);
        pc.printf("Temp in C -> %f \r\n", temperature);
        pc.printf("Dew point %f \r\n", sht21.SHT2x_GetDewpoint(relHumidity, temperature));

        myled = 0;
        wait(1);
    }
}



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