1. Writing Plugins

Plugins are currently an experimental feature, and only support for reading sensors has been implemented.

A plugin is a Python module that expands the ESDK ecosystem to support additional sensors.

1.1. Requirements

At the bare minimum, a plugin contains a class with a function called readSensors that returns a dictionary containing the sensor data. Should no data be available, a value of -1 should be returned in place of the dictionary.

The sensor data dictionary should contain certain data:

{
        "sensorname": {
                "sensor": "sensorversion"
        }
}

The sensorname key should be a descriptive, short name for the sensor. For example, the ESDK sensor boards are thv, co2 and pm2.

The sensorversion value should be a string containing a revision of the sensor board or plugin module. For example, the ESDK sensor boards are THV0.2, CO20.2 and PM20.2 (board name plus a hardware version number).

Sensor data can be inserted into the innermost object, alongside the sensor key. For example, the sensor data structure for a PIR sensor plugged into the ESDK-EEA board would look like the following:

{
        "pir": {
                "motion": "1",
                "sensor": "pirplugin0.1"
        }
}

1.2. Example

A simple example that reads a GPIO pin is provided below:

import RPi.GPIO as GPIO
GPIO1 = 20

class PIR:
def __init__(self):
        GPIO.setmode(GPIO.BCM)
        GPIO.setup(GPIO1, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

def readSensors(self):
        pirState = GPIO.input(GPIO1)
        return {"pir": {"motion": str(pirState), "sensor": "pirplugin0.1"}}

1.3. Usage

By default, ModMAIN looks for a plugins directory in the current working directory of the Python script that has instantiated the class, but this can be overridden by providing the pluginDir argument when instantiating the class.

mb = MAIN.ModMAIN(config=config, debug=True, loggingLevel='off', pluginDir="/home/pi/plugins")

Plugins are loaded using the loadPlugins function, which attempts to import each module found in the specified directory.

Calling the function readAllModules attempts to read all the default sensor modules (i.e. THV, CO2 and PM2), and then attempts to read the plugin sensors. The function then returns a dictionary containing all the available sensor data.

1.4. Exceptions

Exceptions are handled internally within the ModMAIN class, and errors are logged where necessary. If a plugin isn’t working, check for errors in the logs to pinpoint where the issue lies.