The Pymata4 Class

To use the Pymata4 class, you must first import it:

from pymata4 import pymata4

and then instantiate it:

board = pymata4.Pymata4()

The board variable contains a reference to the Pymata4 instance. You use this reference to access the Pymata4 methods of the instance.

For example, to cleanly shutdown your Pymata4 application, you might call the shutdown method:

board.shutdown()

Of course, you can name the instance variable, anything that is meaningful to you. There is nothing magic about the name board.

Understanding The Pymata4 init Parameters

 def __init__(self, com_port=None, baud_rate=115200,
                 arduino_instance_id=1, arduino_wait=4,
                 sleep_tune=0.000001,
                 shutdown_on_exception=True, ip_address=None,
                 ip_port=None):

There are many optional parameters available when you instantiate Pymata4.

If you are using FiramataExpress with a single Arduino, then in most cases, you can accept all of the default parameters provided in the __init__ method.

But there are times when you may wish to take advantage of the flexibility provided by the __init__ method parameters, so let's explore the definition and purpose of each parameter:

The Auto-Discovery Parameters - com_port, baud_rate, and arduino_instance

By accepting the default values for these parameters, pymata4 assumes you have flashed your Arduino with FirmataExpress.

com_port

The com_port parameter specifies a serial com_port, such as COM4 or '/dev/ttyACM0' used for PC to Arduino communication. If the default value of None is accepted, pymata4 will attempt to find the connected Arduino automatically.

baud_rate

The default for this parameter is 115200, matching the speed set in the FirmataExpress sketch. If you wish to use StandardFirmata instead of FirmataExpress, you will set the baud_rate to 57600. If you specify the baud_rate and accept the default com_port value, pymata4 attempts to find a connected Arduino.

arduino_instance_id

This parameter is only valid when using FirmataExpress. This parameter allows pymata4 to connect to an Arduino with a matching ID.

This is useful if you have multiple Arduino's plugged into your computer, and you wish to have a specific Arduino selected for connection.

StandardFirmata does not have this capability, and auto-discovery connects to the first Arduino it finds. This is not always the desired result.

The default value for the arduino_instance_id for both pymata4 and FirmataExpress is 1.

Instructions for changing the FirmataExpress value may be found in the Installing FirmataExpress section of this document.

arduino_wait

This parameter specifies the amount of time that pymata4 assumes it takes for an Arduino to reboot the FirmataExpress (or StandardFirmata) sketch from a power-up or reset.

The default is 4 seconds. If the Arduino is not fully booted when com_port auto-discovery begins, auto-discovery will fail.

sleep_tune

This is the sleep value expressed in seconds, that is used at several strategic points in pymata4. For example, the serial receiver continuously checks the serial port receive buffer for an available character to process. If there is no character in the buffer, pymata4 sleeps for the sleep_tune period before checking again.

The default value is 0.000001 seconds.

shutdown_on_exception

When this parameter is set to True, the shutdown method is automatically called when an exception is detected. This disables reporting for both digital and analog pins, in addition to closing the serial port.

By setting this parameter to False, the Arduino may continue to send data to your application even after restarting it.

The default is True and recommended to be used.

ip_address

If you are using StandardFirmataWiFi, set this parameter to the IP address of your WiFi connected device.

ip_port

If you are using StandardFirmataWiFi, set this parameter to the IP port of your WiFi connected device.

Examples

Each example on GitHub demonstrates instantiating the Pymata4 class.

A blink demo is provided for StandardFirmata WiFi connections.