Module `urest.examples.pwmled`

An example of a 'noun' class, able to serve as the basis for PWM control of an LED attached to a suitable GPIO pin

Overview

This is a reasonably minimal example of a 'noun' class, which inherits from APIBase. It also requires the Pin library from MicroPython: but should be able to be adapted to other GPIO libraries which provide a similar interface.

In contrast to the SimpleLED class, the PWMLED class shows the use of the ayncio create_tasks() hook within a APIBase 'noun' to set off slow running tasks. This allows the state update to be returned to the network client via the API 'immediately' (at least subject to the other tasks outstanding and network conditions); without waiting for the actual internal state to complete. This is a much more realistic scenario for use in the control of external devices: especially devices such as motors which may take seconds (or longer) to obtain the correct state.

Api

The 'noun' will return two objects in the JSON state, in response to get_state requests

actual : The current state of the output, which will be 0 for fully off and 1 for fully on
desired: The next state, if any, that the output is currently transitioning to; either 0 for fully off and 1 for fully on

This gives a full state table as follows

Actual State	Desired State	Description
0	0	Output fully `off`
0	1	Output commanded `on`; currently turning from `off` to `on`
1	0	Output commanded `off`; currently turning from `on` to `off`
1	1	Output fully `on`

Tested Implementations

This version is written for MicroPython 3.4, and has been tested on:

Raspberry Pi Pico W

Licence

This class, and all included code, is made available under the terms of the MIT Licence

Copyright (c) 2023 David Love

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Expand source code

"""
An example of a 'noun' class, able to serve as the basis for PWM control of an
LED attached to a suitable GPIO pin

Overview
--------

This is a reasonably minimal example of a 'noun' class, which inherits from
`urest.api.base.APIBase`. It also requires the `Pin` library from MicroPython:
but should be able to be adapted to other GPIO libraries which provide a similar
interface.

In contrast to the `urest.examples.simpleled.SimpleLED` class, the
`urest.examples.pwmled.PWMLED` class shows the use of the `ayncio`
`create_tasks()` hook within a `urest.api.base.APIBase` 'noun' to set off slow
running tasks. This allows the state update to be returned to the network client
via the API 'immediately' (at least subject to the other tasks outstanding and
network conditions); without waiting for the _actual_ internal state to
complete. This is a much more realistic scenario for use in the control of
external devices: especially devices such as motors which may take seconds (or
longer) to obtain the correct state.

API
---

The 'noun' will return two objects in the JSON state, in response to `get_state`
requests

  * `actual` : The _current_ state of the output, which will be `0` for fully off
and `1` for fully on
  * `desired`: The _next_ state, if any, that the output is
currently transitioning to; either `0` for fully off and `1` for fully on

This gives a full state table as follows

| Actual State | Desired State | Description                                                  |
|--------------|---------------|--------------------------------------------------------------|
| 0            | 0             | Output fully `off`                                           |
| 0            | 1             | Output commanded `on`; currently turning from `off` to `on`  |
| 1            | 0             | Output commanded `off`; currently turning from `on` to `off` |
| 1            | 1             | Output fully `on`                                            |



Tested Implementations
----------------------

This version is written for MicroPython 3.4, and has been tested on:

  * Raspberry Pi Pico W

Licence
-------

This class, and all included code, is made available under the terms of the MIT Licence

> Copyright (c) 2023 David Love

> Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

> The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
"""

# Import the Asynchronous IO Library, preferring the MicroPython library if
# available
try:
    from machine import Pin, PWM
    import uasyncio as asyncio
except ImportError:
    print("Ignoring MicroPython include: machine")

from ..api.base import APIBase

PWM_STEP = 6550
""" Determines the increment (or decrement) for each step in the PWM 'on' or 'off' movement"""


class PWMLED(APIBase):
    def __init__(self, pin: int):
        self._gpio = PWM(Pin(pin))
        self._gpio.duty_u16(0)
        self._gpio.freq(100)
        self._gpio_lock = asyncio.Lock()

        self._duty = 0

        self._state_attributes = dict(desired=0, current=0)

    async def _slow_on(self):
        # Wait for the GPIO lock if we need to
        await self._gpio_lock.acquire()

        # Increase the duty cycle from 0 to near the
        # maximum in steps lasting 1s. We will also
        # allow other co-routines to run whilst we
        # are waiting for the next step to take place

        self._duty = 0

        while self._duty < (65000):
            print(f"duty on: {self._duty}")

            self._duty += PWM_STEP
            self._gpio.duty_u16(self._duty)

            await asyncio.sleep_ms(1000)
        else:
            self._state_attributes["current"] = 1

        # Set the duty cycle to maximum before we leave,
        # and release the GPIO lock
        self._duty = 2 ** 16
        self._gpio.duty_u16(self._duty)

        self._gpio_lock.release()

    async def _slow_off(self):
        # Wait for the GPIO lock if we need to
        await self._gpio_lock.acquire()

        # Decrease the duty cycle from the maximum to
        # near 0 in steps lasting 1s. We will also
        # allow other co-routines to run whilst we
        # are waiting for the next step to take place

        self._duty = 2 ** 16

        while self._duty > 6000:
            print(f"duty off: {self._duty}")

            self._duty -= PWM_STEP
            self._gpio.duty_u16(self._duty)

            await asyncio.sleep_ms(1000)
        else:
            self._state_attributes["current"] = 0

        # Set the duty cycle to 0 before we leave,
        # and release the GPIO lock
        self._duty = 0
        self._gpio.duty_u16(self._duty)

        self._gpio_lock.release()

    def set_state(self, state_attributes: dict):
        try:
            loop = asyncio.get_event_loop()

            self._state_attributes["desired"] = state_attributes["desired"]

            if self._state_attributes["desired"] == 0:
                self._state_attributes["current"] = 1

                loop.create_task(self._slow_off())
            else:
                self._state_attributes["current"] = 0

                loop.create_task(self._slow_on())

        except KeyError:
            # On exception try to return to a known good
            # state
            self._gpio.duty_u16(0)
            self._duty = 0

            self._state_attributes["desired"] = 0
            self._state_attributes["current"] = 0

    def get_state(self) -> dict:
        return self._state_attributes

    def delete_state(self):
        self._gpio.duty_u16(0)
        self._gpio.freq(100)
        self._duty = 0

        self._state_attributes["desired"] = 0
        self._state_attributes["current"] = 0

    def update_state(self, state_attributes: dict):
        loop = asyncio.get_event_loop()

        if self._state_attributes["desired"] == 0:
            self._state_attributes["desired"] = 1
            self._state_attributes["current"] = 0

            loop.create_task(self._slow_on())
        else:
            self._state_attributes["desired"] = 0
            self._state_attributes["current"] = 1

            loop.create_task(self._slow_off())

Global variables

var PWM_STEP: Determines the increment (or decrement) for each step in the PWM 'on' or 'off' movement

Classes

class PWMLED (pin: int)

The Abstract Base Class for the nouns, used in the response from the server.

This base class defines the minimum interface used in marshalling requests from the clients by the RESTServer class. The API defined by the server consists of 'nouns' representing the resources defined by the sub-classes of this base class, and the methods which act upon those resources (which map to the 'verbs' of the HTTP requests made to the RESTServer class.

Where data is returned to the client by the, e.g by the get_state method, JSON will ultimately be used as the encoding format. Sub-classes do not need to implement the saving of the object state to the client: however to assist they should be aware of the type of the each value returned as part of a key/value pair in the Dictionary.

When returning data to the client, the value of each entry in the Dictionary will attempt to be inferred using the normal Python type library. If the type can be identified, then an appropriate JSON type will be used: otherwise the value of that Dictionary entry will be returned as a string.

Warning: Data will be returned to the client 'as is'

No further checking on the validity (or otherwise) of the content of the Dictionary will be undertaken past this point. Anything that appear to be in a valid Dictionary will be returned to the client. It is the module consumers responsibility to ensure the returned data follows the form expected by those clients.

Expand source code

class PWMLED(APIBase):
    def __init__(self, pin: int):
        self._gpio = PWM(Pin(pin))
        self._gpio.duty_u16(0)
        self._gpio.freq(100)
        self._gpio_lock = asyncio.Lock()

        self._duty = 0

        self._state_attributes = dict(desired=0, current=0)

    async def _slow_on(self):
        # Wait for the GPIO lock if we need to
        await self._gpio_lock.acquire()

        # Increase the duty cycle from 0 to near the
        # maximum in steps lasting 1s. We will also
        # allow other co-routines to run whilst we
        # are waiting for the next step to take place

        self._duty = 0

        while self._duty < (65000):
            print(f"duty on: {self._duty}")

            self._duty += PWM_STEP
            self._gpio.duty_u16(self._duty)

            await asyncio.sleep_ms(1000)
        else:
            self._state_attributes["current"] = 1

        # Set the duty cycle to maximum before we leave,
        # and release the GPIO lock
        self._duty = 2 ** 16
        self._gpio.duty_u16(self._duty)

        self._gpio_lock.release()

    async def _slow_off(self):
        # Wait for the GPIO lock if we need to
        await self._gpio_lock.acquire()

        # Decrease the duty cycle from the maximum to
        # near 0 in steps lasting 1s. We will also
        # allow other co-routines to run whilst we
        # are waiting for the next step to take place

        self._duty = 2 ** 16

        while self._duty > 6000:
            print(f"duty off: {self._duty}")

            self._duty -= PWM_STEP
            self._gpio.duty_u16(self._duty)

            await asyncio.sleep_ms(1000)
        else:
            self._state_attributes["current"] = 0

        # Set the duty cycle to 0 before we leave,
        # and release the GPIO lock
        self._duty = 0
        self._gpio.duty_u16(self._duty)

        self._gpio_lock.release()

    def set_state(self, state_attributes: dict):
        try:
            loop = asyncio.get_event_loop()

            self._state_attributes["desired"] = state_attributes["desired"]

            if self._state_attributes["desired"] == 0:
                self._state_attributes["current"] = 1

                loop.create_task(self._slow_off())
            else:
                self._state_attributes["current"] = 0

                loop.create_task(self._slow_on())

        except KeyError:
            # On exception try to return to a known good
            # state
            self._gpio.duty_u16(0)
            self._duty = 0

            self._state_attributes["desired"] = 0
            self._state_attributes["current"] = 0

    def get_state(self) -> dict:
        return self._state_attributes

    def delete_state(self):
        self._gpio.duty_u16(0)
        self._gpio.freq(100)
        self._duty = 0

        self._state_attributes["desired"] = 0
        self._state_attributes["current"] = 0

    def update_state(self, state_attributes: dict):
        loop = asyncio.get_event_loop()

        if self._state_attributes["desired"] == 0:
            self._state_attributes["desired"] = 1
            self._state_attributes["current"] = 0

            loop.create_task(self._slow_on())
        else:
            self._state_attributes["desired"] = 0
            self._state_attributes["current"] = 1

            loop.create_task(self._slow_off())

Ancestors

APIBase

Inherited members

APIBase:
- delete_state
- get_state
- set_state
- update_state