The SI7021 is a high quality sensor for humidity and temperature. Of course there is a library for it for the Arduino IDE. As you can see in the picture, it has an I2C interface. The back side of the sensor:
The connection is the same as with other I2C devices, use A4 SDA and A5 SCL or on the ESP D2 for SDA and D1 for SCL.
Below a slightly updated version of the example which comes with the library to have it compile correctly on the ESP8266.
#include
#include
#if defined(ESP8266)
// For the ESP8266 we need these to be defined
#define SDA 4
#define SCL 5
#endif
SI7021 sensor;
void setup() {
Serial.begin(9600);
Serial.println("Ready!");
#if defined(ESP8266)
// For the ESP8266 we need to start the sensor with SDA and SCL pin numbers
sensor.begin(SDA,SCL);
#else
// For Arduino we can just call begin.
sensor.begin();
#endif
}
void loop() {
// temperature is an integer in hundredths
float temperature = sensor.getCelsiusHundredths();
temperature = temperature / 100;
Serial.println("------------");
Serial.print("Temperature in Celsius: ");
Serial.println(temperature);
// humidity is an integer representing percent
int humidity = sensor.getHumidityPercent();
Serial.print("Humidity: ");
Serial.print(humidity);
Serial.println("%");
// this driver should work for SI7020 and SI7021, this returns 20 or 21
int deviceid = sensor.getDeviceId();
Serial.print("This is a SI70");
Serial.println(deviceid);
Serial.println();
Serial.println("Heating");
// enable internal heater for testing
sensor.setHeater(true);
delay(20000);
sensor.setHeater(false);
Serial.println("Done heating");
// see if heater changed temperature
temperature = sensor.getCelsiusHundredths();
temperature = temperature / 100;
Serial.print("Temperature in Celsius: ");
Serial.println(temperature);
Serial.println();
Serial.println("Cooling");
//cool down
delay(20000);
// get humidity and temperature at same time (also saves power)
si7021_env data = sensor.getHumidityAndTemperature();
Serial.println();
Serial.print("Temperature in Celsius: ");
Serial.println(data.celsiusHundredths/100);
Serial.print("Humidity: ");
Serial.print(data.humidityBasisPoints/100);
Serial.println("%");
Serial.println();
Serial.println("Pausing");
delay(5000);
}
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