Pressure

Pressure

Javascript Example

Device Compatibility

Overview

The Pressure driver reports values for:

  • Pressure
  • Altitude
  • Temperature

Based on component location, the temperature values from the Humidity driver are recommended over the Pressure driver

Available ZeroMQ Ports

  • Base port: 20025
  • Keep-alive port: 20026
  • Error port: 20027
  • Data Update port: 20028
Initial Variables

Before we go into connecting to each port, the variables defined below are needed in order to access the ZeroMQ and MATRIX Protocol Buffer libraries for Javascript. We also define a few helpful variables for easy references. 

var zmq = require('zeromq');// Asynchronous Messaging Framework
var matrix_io = require('matrix-protos').matrix_io;// Protocol Buffers for MATRIX function
var matrix_ip = '127.0.0.1';// Local IP
var matrix_pressure_base_port = 20025;// Port for Pressure driver

Base Port

Here is where the configuration for our Pressure example goes. Once we connect to the Base Port, we will pass a configuration to the pressure driver. With this we can set the update rate and timeout configuration. 

// Create a Pusher socket
var configSocket = zmq.socket('push');
// Connect Pusher to Base port
configSocket.connect('tcp://' + matrix_ip + ':' + matrix_pressure_base_port);
// Create driver configuration
var config = matrix_io.malos.v1.driver.DriverConfig.create({
// Update rate configuration
delayBetweenUpdates: 2.0,// 2 seconds between updates
timeoutAfterLastPing: 6.0,// Stop sending updates 6 seconds after pings.
});
// Send driver configuration
configSocket.send(matrix_io.malos.v1.driver.DriverConfig.encode(config).finish());

Keep-alive Port

The next step is to connect and send a message to the Keep-alive Port. That message, an empty string, will grant us a response from the Data Update Port for the current pressure value. An interval for pinging is then set to continuously obtain that data. 

// Create a Pusher socket
var pingSocket = zmq.socket('push');
// Connect Pusher to Keep-alive port
pingSocket.connect('tcp://' + matrix_ip + ':' + (matrix_pressure_base_port + 1));
// Send initial ping
pingSocket.send('');
// Send ping every 5 seconds
setInterval(function(){
pingSocket.send('');
}, 5000);

Error Port

Connecting to the Error Port is optional, but highly recommended if you want to log any errors that occur within MATRIX CORE. 

// Create a Subscriber socket
var errorSocket = zmq.socket('sub');
// Connect Subscriber to Error port
errorSocket.connect('tcp://' + matrix_ip + ':' + (matrix_pressure_base_port + 2));
// Connect Subscriber to Error port
errorSocket.subscribe('');
// On Message
errorSocket.on('message', function(error_message){
console.log('Error received: ' + error_message.toString('utf8'));// Log error
});

Data Update Port

A connection to the Data Update Port will allow us to receive the current pressure data we want.

// Create a Subscriber socket
var updateSocket = zmq.socket('sub');
// Connect Subscriber to Data Update port
updateSocket.connect('tcp://' + matrix_ip + ':' + (matrix_pressure_base_port + 3));
// Subscribe to messages
updateSocket.subscribe('');
// On Message
updateSocket.on('message', function(buffer){
var data = matrix_io.malos.v1.sense.Pressure.decode(buffer);// Extract message
    console.log(data);// Log new pressure data
});

Data Output

The javascript object below is an example output you'll receive from the Data Update Port. 
{
pressure: 101173.75,
altitude: 12.812000274658203,
temperature: 37.3120002746582 
}

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