hts221

Connect to HTS221 sensor on Arduino hardware I2C bus

Since R2021a

Description

The hts221 object reads relative humidity and ambient temperature using the HTS221 sensor connected to the I2C bus of the Arduino^® hardware. HTS221 is used to read relative humidity. The HTS221 also has an embedded temperature sensor. Attach the HTS221 sensor to the I2C pins on the hardware. You can read the data from the sensor in MATLAB^® using the Object Functions.

Creation

Syntax

humiditySensor = hts221(a)

humiditySensor = hts221(a,Name,Value)

Description

humiditySensor = hts221(a) creates a sensor object with default property values.

Example: humiditySensor = hts221(a);.

humiditySensor = hts221(a,Name,Value) creates a sensor object with properties using one or more Name,Value pair arguments.

Example: humiditySensor = hts221(a, 'Bus', 1);.

Input Arguments

a — Connection to the hardware

object

Connection to the hardware specified as an object.

Example: humiditySensor = hts221(a) creates a connection to the HTS221 sensor on the hardware represented as an object, a.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Bus — I2C Bus Number

0 (default) | 1

I2C bus number, specified as 0 or 1. The default value is 0.

Example: humiditySensor = hts221(a, 'Bus', 1) creates the sensor object on Bus 1 of the hardware.

Data Types: double

Properties

Note

The properties can also be used as name-value pair arguments while creating an hts221 object.

Bus — I2C Bus Number

0 (default) | 1

I2C bus number, specified as 0 or 1. The default value is 0.

Data Types: double

Note

Except for TimeFormat, all the other properties are non-tunable, which means you cannot change their values once the object is locked. Objects are locked when you call the read function, and the release function unlocks them. If a property is tunable, you can change its value at any time.

SampleRate — Rate at which sample is read

100 (default) | positive integer in the range [1, 200]

The rate in samples/s at which data is read from the sensor.

Data Types: double

SamplesPerRead — Number of samples read in a single execution of the read function

10 (default) | [1 500]

Number of samples read from the sensor in a single execution of the read function.

Data Types: double

ReadMode — Specify which data samples to be returned

'latest' (default) | 'oldest'

Specify whether to return the latest or the oldest data samples. The number of samples depends on the SamplesPerRead value. The data read from the sensor is stored in the MATLAB buffer.

• latest —

  Provides the latest data samples available in the buffer. All previous data samples in the buffer are discarded. For example, if SamplesPerRead = 3, the latest three data samples read by the sensor are returned.

  The following figure illustrates how latest data samples are returned assuming S1 is the first sensor data stored in the buffer, S2 is the second data and so on and Sn is the last data stored in the buffer and SamplesPerRead property is set to 3 during sensor object creation.

  

• oldest —

  Provides the oldest data samples available in the buffer. In this case, no data samples are discarded. For example, if SamplesPerRead = 3, the first three data samples read are returned for the first read, the next three data samples are returned for the second read, and so on.

  The following figure illustrates how oldest data samples are returned assuming S1 is the first sensor data stored in the buffer, S2 is the second data and so on and Sn is the last data stored in the buffer and SamplesPerRead property is set to 3 during sensor object creation.

  

Data Types: character vector | string

SamplesRead — Samples read

double

This property is read-only.

Samplesread property outputs the values of samples read so far by executing read function. Samplesread is set to 0, when the object is created or when you release the object.

Data Types: double

OutputFormat — Set output format

'timetable' (default) | 'matrix'

Set the output format of the data returned by executing the read function.

When the OutputFormat is set to timetable, the data returned has the following fields:

• Time — Time stamps in datetime or duration format

• Humidity — N-by-1 array in units of %

• Temperature — N-by-1 array in units of degree Celsius

When the OutputFormat is set to matrix, the data is returned as matrices of humidity, temperature, and time stamps. The units for the sensor readings are the same as the timetable format.

N is the number of samples per read specified by SamplesPerRead.

Data Types: character vector | string

TimeFormat — Set time format

'datetime' (default) | 'duration'

Set the format of the time displayed when the sensor data is read.

• datetime — Displays the date and time at which the data is read.

• duration — Displays the time elapsed in seconds after the sensor object is locked. The sensor object gets locked at the first call of the read function either after the object creation or after the execution of the release function.

Data Types: character vector | string

Object Functions

readHumidity	Read one sample of relative humidity data from the sensor
readTemperature	Read one sample of temperature from sensor
read	Read real-time sensor data at a specified rate
release	Release the sensor object
flush	Flush the host buffer
info	Read information related to sensor

Examples

Create Connection to HTS221 Sensor

Create an arduino object with the I2C library.

a = arduino('COM4', 'Uno', 'Libraries', 'I2C');

Create the sensor object.

humiditySensor = hts221(a)

humiditySensor =
 
  hts221 with properties:
 
                         I2CAddress: 95  ("0x5F")
                                Bus: 0
                             SCLPin: "A5"
                             SDAPin: "A4"

                         SampleRate: 100  (Samples/s)
                     SamplesPerRead: 10  
                           ReadMode: 'latest'            
                        SamplesRead: 0      
                   SamplesAvailable: 0 
Show all properties all functions

Create HTS221 Sensor Connection with Additional Name-Value Pair Arguments

Create a sensor object with additional properties specified as name-value pair arguments.

clear humiditySensor;
humiditySensor = hts221(a,'SampleRate',50,'SamplesPerRead',5,'ReadMode','oldest')

humiditySensor = 

  hts221 with properties: 

                 I2CAddress: 95  ("0x5F") 
                        Bus: 0
                     SCLPin: "A5" 
                     SDAPin: "A4" 

                 SampleRate: 50  (Samples/s)
             SamplesPerRead: 5  
                   ReadMode: 'oldest'            
                SamplesRead: 0      
           SamplesAvailable: 0 

Show all properties, functions

More About

Code Generation Using MATLAB Function Block

• Use hts221 in a MATLAB Function block with the Simulink^® Support Package for Arduino Hardware to generate code that can be deployed on Arduino Hardware.

• The property ReadMode cannot be changed and is always set to latest.

• The property SamplesPerRead cannot be changed and is always set to 1. So, no framing is provided.

• The property OutputFormat is always set to matrix.

• The property TimeFormat is always set to duration.

• The property SamplesAvailable is not accessible from sensor object.

Version History

Introduced in R2021a