Si702X sensor

Arduino library for Si7020 and Si7021 sensors.

Used to measure temperature in various scales, measure the relative humidity and implements a heater for frost removal.

Usage

This is an example how you could use this library.

#include <Arduino.h>
#include "Si702X.hpp"

//Create sensor object.
Si702X sensor = Si702X();
void setup() {

    //The Si702X does not start the i2c bus on its own.
    Wire.begin();

    //Start the serial connection for printing the readings
    Serial.begin(9600);

    //Print the sensors firmware version
    Serial.print("The sensor has ");
    Serial.println( sensor.getVersion() );
   
    //Print the sensors device ID
    Serial.print("The device ID is ");
    Serial.println( sensor.getDeviceID() );

    //Print the sensors serial number
    Serial.print("The Serial number is ");
    Serial.print( sensor.getSerial() );
    Serial.println("\n");
}

void loop() {
    //Wait for half a second
    delay(500);

    //Print the temperature reading in Fahrenheit
    Serial.print("The temperature is ");
    Serial.print( sensor.getFahrenheit() );
    Serial.println(" Fahrenheit.");

    //Print the temperature reading in celcius
    Serial.print("The temperature is ");
    Serial.print( sensor.getCelcius() );
    Serial.println(" Celcius.");

    //Print the relative humidity
    Serial.print("The relative humidity is ");
    Serial.print( sensor.getRH() );
    Serial.println("\n");
}

Documentation

Here are the functions explained that can be used with this library

Constructor

The constructor has the option to give a TwoWire object to send commands through. The default is the standard Arduino Wire object and does not have to be given to the constructor if used. The Si702X assumes the .begin() function has been used on the TwoWire bus.

Temperature functions

All these functions return the temperature in celcius and converts them to the temperature scale in their name. The resolution is determined by the setResolution function. These functions can be influenced by the heater element if used. These functions are possible to use whilst the sensor is const.

List of temperature functions with the part after "get" being the scale it returns.

• getCelcius()
• getKelvin()
• getFahrenheit()
• getNewton()
• getRankine()
• getDelisle()
• getReaumur()
• getRomer()

Relative Humidity function

The function getRH() gets the relative humidity that the sensor has measured. The reading is returned in a const float. The resolution is determined by the setResolution function. So far I havent found the need or the wil to implement more scales to view the humidity. These functions can be influenced by the heater element if used.

Control functions

Functions in this catagory are configure the sensors heater and reading resolution. These functions are not possible to use if the sensor is const. These functions make use of the i2c error codes with some of my own added. The error code have the following meaning:

Error code	Meaning
0	Succesfully executed function
1	Data too long to fit in transmit buffer
2	Received NACK on transmit of address
3	Received NACK on transmit of data
4	Other error
5	Given heater level too high
6	Voltage too low

reset()

This function resets all the settings used for this sensor.

enableHeater()

This function enables the heater and lets it heat up to the given level. If the given voltage to the sensor is not high enough the heater wil not enable.

disableHeater();

This function disables the heater but remembers the level that has been set.

setHeater(level)

Sets the heat of the sensor.
The heater can be set to a level between 0 - 15. The higher number the higher the heat.
A level above 15 will return 5 and not change the heater level.
Heater needs to be enabled to take effect.
If no argument is given the level will be 0 i.e. off

The heater level has the following typical current draw in mA.
Assumes VDD = 3.3 V.

Heater level (binary)	Current draw (mA)
0000	3.09
0001	9.18
0010	15.24
...	...
0100	27.39
...	...
1000	51.69
...	...
1111	94.40

setResolution(a, b)

Sets the resolution of temperature and humidity measurements. Measurement Resolution can be configured using the following table:

Config	RH precision	Temp precision
00	12 bit	14 bit
01	8 bit	12 bit
10	10 bit	13 bit
11	11 bit	11 bit

Other functions

getVersion()

Returns the version of the sensor in a string

getDeviceID()

Returns the device ID of the sensor in a string

getSerial()

Returns the serial number of the sensor in a 16bit signed int.

Used information

• Datasheet.