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Pressure

The Pressure driver reports values for:

  • Pressure
  • Altitude
  • Temperature

The driver follows the MALOS protocol.

0MQ Port

20025

Protocol buffers

message Pressure {
  float pressure = 1;
  float altitude = 2;
  float temperature = 3;
}

The message is defined in driver.proto.

Keep-alives

This driver needs keep-alive messages as specified in the MALOS protocol. If you start sending keep-alive messages it will start returning data every second so you can omit the configuration for this device.

Errors

This driver report errors when an invalid configuration is sent.

Read

The driver will send a serialized message of type Pressure.

message Pressure {
  float pressure = 1;
  float altitude = 2;
  float temperature = 3;
}

This is a sample output given by the example described below.

$ node test_pressure.js 
Sending pings every 5 seconds
{ pressure: 74773.5, altitude: 2490.375, temperature: 35.9375 }
{ pressure: 74776, altitude: 2490.3125, temperature: 35.9375 }

JavaScript example

Enhanced description of the sample source code.

First, define the address of the MATRIX Creator. In this case we make it be 127.0.0.1 because we are connecting from the local host but it needs to be different if we connect from another computer. There is also the base port reserved by MALOS for the Pressure driver.

var creator_ip = '127.0.0.1'
var creator_pressure_base_port = 20013 + (4 * 3)

Load the protocol buffers used in the example.

var protoBuf = require("protobufjs")

// Parse proto file
var protoBuilder = protoBuf.loadProtoFile('../../protocol-buffers/malos/driver.proto')
// Parse matrix_malos package (namespace).
var matrixMalosBuilder = protoBuilder.build("matrix_malos")

Subscribe to the errors reported by the driver.

var zmq = require('zmq')

var errorSocket = zmq.socket('sub')
errorSocket.connect('tcp://' + creator_ip + ':' + (creator_pressure_base_port + 2))
errorSocket.subscribe('')
errorSocket.on('message', function(error_message) {
  process.stdout.write('Message received: Pressure error: ' + error_message.toString('utf8') + "\n")
});

All the drivers are configured using the message DriverConfig (see driver.proto). This is what the message looks like if we omit the fields that are not used in this example.

message DriverConfig {
  float delay_between_updates = 1;
  float timeout_after_last_ping = 2;
}

The following snippet is telling the driver to send an update each 2 seconds and stop sending updates if it doesn't receive a keep-alive message for 6 seconds.

var configSocket = zmq.socket('push')
configSocket.connect('tcp://' + creator_ip + ':' + creator_pressure_base_port)

var driverConfigProto = new matrixMalosBuilder.DriverConfig

driverConfigProto.delay_between_updates = 2.0
driverConfigProto.timeout_after_last_ping = 6.0

configSocket.send(driverConfigProto.encode().toBuffer())

Where is where the updates are received by subscribing to the data update port of the driver. The subscription is initiated by the line updateSocket.subscribe('').

var updateSocket = zmq.socket('sub')
updateSocket.connect('tcp://' + creator_ip + ':' + (creator_pressure_base_port + 3))
updateSocket.subscribe('')
updateSocket.on('message', function(buffer) {
  var data = new matrixMalosBuilder.Pressure.decode(buffer)
  console.log(data)
});

An empty keep-alive message is sent to the driver every 5 seconds to make sure it keeps sending data updates.

var pingSocket = zmq.socket('push')
pingSocket.connect('tcp://' + creator_ip + ':' + (creator_pressure_base_port + 1))
process.stdout.write("Sending pings every 5 seconds");
pingSocket.send(''); // Ping the first time.
setInterval(function(){
  pingSocket.send('');
}, 5000);