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All my projects (ongoing & finished) are listed here.

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In event driven programming events are crucial. My requirements was Micropython platform on ESP32 micro-controller, so i could not use any other events library out-there. I've stumbled one very basic, very simple library and gave it a try… and it worked out-of-the-box for my case. When testing various event management libs out there I've stumbled on something similar, but it did not worked within classes. Python is nothing but classes everywhere :)

I was testing and extended this very simple python script, that perfectly works as main element in event driven development.

Strengths of library:

  • Observer can be declared before event type is created
  • Events can be fired even if there is no observers.
  • Works as pure python script
  • Works on micropython platform
  • Event name can be any string

I'm using this solution for event for timer, that fires each second and observe “ticker” where i need to update clock. I use clock in multiple places in my micropython script and i can get away with just one hardware timer used.

Honorable mentions goes to Pithikos from StackOverflow this answer

I have extended this library with possibility to forget event.

EventObserver.py
class Observer():
    _observers = []
 
    def __init__(self):
        self._observers.append(self)
        self._observed_events = []
 
    def observe(self, event_name, callback_fn):
        self._observed_events.append({'event_name': event_name, 'callback_fn': callback_fn})
 
    def forget(self, event_name):
        for dict_item in self._observed_events:
            for key, val in dict_item.items():
                if val == event_name:
                    self._observed_events.remove(dict_item)
 
 
class Event():
    def __init__(self, event_name, *callback_args):
        for observer in Observer._observers:
            for observable in observer._observed_events:
                if observable['event_name'] == event_name:
                    observable['callback_fn'](*callback_args)

Here is example of how to use this library

example.py
import EventObserver
 
# class object MUST inherit Observer object if you use it within class
class Room(Observer):
    def __init__(self):
        print("Room is ready.")
        Observer.__init__(self)  # DON'T FORGET THIS
        # observer can be declared already in class init method with following line
        # this.observe('someone sneezed', this.someone_sneezed)
 
    def someone_arrived(self, who):
        print("{} has arrived!".format(who))
 
    def someone_sneezed(self, who):
        print("{} has just sneezed!".format(who))
 
 
# Observe for specific event
room = Room()
room.observe('arrived', room.someone_arrived)
room.observe('sneezed', room.someone_arrived)
 
# Fire some events
Event('left', 'John')       # no events are attached to event "someone left" 
Event('arrived', 'Lenard')  # will output "Lenard has arrived!"
Event('sneezed', 'Jenny')   # will output "Jenny has just sneezed!"
 
# Remove known event
room.forget('arrived')
 
# no events based on 'someone arrived' will be fired
'''

I never forgot my old dream- to have my own DIY telemetry system

And here after like 7 years, when technology advanced (my knowledge, also)- I have finished building my project. And my main problems are solved with two unit of ESP32 microcontrolers and Android phone. Hardware is two ESP32 units with integrated SX1278 interface and one Beitian BN-220 GPS and GLONAS receiver.

I dont realy like C programming, so my choise of microcontroller was based on availability to use other languages for programming. Initial idea was to use Espruino firmware and use Javascript language for programming. But the issue at the time of research was BLE interface was not available (Harware supports it). Other options was Micropython and LUA. I have burned Micropython firmware into ESP32

So, here is how everything works: microcontroler ESP32 read GPS receiver data, extract required informaation and… taaadaaaa… =)

LoRa is used to transfer data to ground unit. Once i've tested range of my LoRa equiped ESP32's units- I've received over 2.2 km LOS at 433mhz. As i'm flying my plane in line of sight- it's plenty for me.

Ground unit listend for air unit frequincy, extract data and via BLE interfaace share this information with my Android device. Device application is created using Droidscript.

Each time i'm testing something new, like programming language, i choose to build solution that would help in my life. This way I can learn more about tool, test is it suitable for me and solve my issue if I succeed.

  • start.txt
  • Last modified: 2021/04/02 23:23
  • by Ignas