Pressure

Pressure

Python 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

Code Example

The following sections show how to implement a connection to each of the Pressure driver's ports. You can download this example here.

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 Python. We also define a few helpful variables for easy references. 

import os # Miscellaneous operating system interface
import zmq # Asynchronous messaging framework
import time # Time access and conversions
import sys # System-specific parameters and functions
from matrix_io.proto.malos.v1 import driver_pb2 # MATRIX Protocol Buffer driver library
from matrix_io.proto.malos.v1 import sense_pb2 # MATRIX Protocol Buffer sensor library
from multiprocessing import Process # Allow for multiple processes at once
from zmq.eventloop import ioloop # Asynchronous events through ZMQ
matrix_ip = '127.0.0.1' # Local device ip
pressure_port = 20025 # Driver Base port
# Handy functions for connecting to the keep-Alive, Data Update, & Error port 
from utils import driver_keep_alive, register_data_callback, register_error_callback

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, timeout, and temperature configuration. 

def config_socket():
    # Define zmq socket
    context = zmq.Context()
    # Create a Pusher socket
    socket = context.socket(zmq.PUSH)
    # Connect Pusher to configuration socket
    socket.connect('tcp://{0}:{1}'.format(matrix_ip, pressure_port))

    # Create a new driver config
    driver_config_proto = driver_pb2.DriverConfig()
    # Delay between updates in seconds
    driver_config_proto.delay_between_updates = 1.0
    # Timeout after last ping
    driver_config_proto.timeout_after_last_ping = 6.0

    # Send driver configuration through ZMQ socket
    socket.send(driver_config_proto.SerializeToString())

Keep-alive Port

The next step is to connect and send a message to the Keep-alive Port. That message will grant us a response from the Data Update Port for the current pressure value. The utils import from the Initial Variables section takes care of this.

Error Port

The Error Port connection is also taken care of by the utils import. Below we define a function to be called and given any error messages that occur within MATRIX CORE. 

def pressure_error_callback(error):
    # Log error
    print('{0}'.format(error))

Data Update Port

A connection to the Data Update Port will allow us to receive the current pressure data we want. The utils import takes care of this as well. We can define a function and expect pressure data to be passed to it.

def pressure_data_callback(data):
    # Extract data
    data = sense_pb2.Pressure().FromString(data[0])
    # Log data 
    print('{0}'.format(data))

Data Output

The Python object below is an example output you'll receive from the Data Update Port. 
pressure: 101268.492188
altitude: 4.81199979782
temperature: 33.625

Start Processes

This is where we begin the asynchronous events for each of the driver ports and where we define the functions we want to use for each port.

if __name__ == '__main__':
    # Initiate asynchronous events
    ioloop.install()
    # Send Base Port configuration 
    config_socket()
    # Start Error Port connection
    Process(target=register_error_callback, args=(pressure_error_callback, matrix_ip, pressure_port)).start()
    # Start Data Update Port connection
    Process(target=register_data_callback, args=(pressure_data_callback, matrix_ip, pressure_port)).start()
    # Start Keep-alive Port connection
    Process(target=driver_keep_alive, args=(matrix_ip, pressure_port)).start()

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