"""
Python Code for Digital Weight Scale

* Typical EECS "project": circuit + computer + program code

* IMPORTANT: though a representative example, not part of EECS 16A.
* Microcontrollers and programming are not part of EECS 16A.
* It's NOT on the exam ...

* [Description](https://people.eecs.berkeley.edu/~boser/courses/49_sp_2019/L3_1_scale.html)
* Parts:
** [M4 ARM microcontroller](https://learn.adafruit.com/adafruit-feather-m4-express-atsamd51)
** [CircuitPython](https://learn.adafruit.com/welcome-to-circuitpython)
** [OLED display](https://learn.adafruit.com/adafruit-oled-featherwing)
** [Load Cell](https://en.wikipedia.org/wiki/Load_cell)
** [Instrumentation Amplifier](http://www.ti.com/product/INA126)
"""

# helper class: detect button press/release events

from digitalio import DigitalInOut, Pull
from time import monotonic, sleep

class Button:

    def __init__(self, pin, *, debounce=0.1, press=None, release=None):
        self.io = DigitalInOut(pin)
        self.io.pull = Pull.UP
        self.debounce = debounce
        self.press = press
        self.release = release
        self.last_state = self.io.value
        self.last_time = monotonic()

    def poll(self):
        if self.last_state == self.io.value:
            return
        if (monotonic()-self.last_time) < self.debounce:
            return
        self.last_time = monotonic()
        self.last_state = self.io.value
        if self.last_state:
            if self.press:
                self.press()
        else:
            if self.release:
                self.release()


# helper class: read load cell voltage (i.e. weight)

from analogio import AnalogIn

class Scale:

    def __init__(self, vin_pin):
        self.vin = AnalogIn(vin_pin)
        self.tare_weight = self.vin.value

    def tare(self):
        print("tare!")
        self.tare_weight = self.vin.value

    def weight(self):
        # average N few ADC readings to reduce "noise"
        N = 5
        w = 0
        for i in range(N):
            w += self.vin.value
            sleep(0.05)
        w /= N
        # subtract tare weight
        w = w - self.tare_weight
        # convert to grams
        w *= 500/14150
        return w


# helper class: display text on OLED display

import board
import displayio
import terminalio
from adafruit_display_text import label
import adafruit_displayio_ssd1306


class TextDisplay:

    def __init__(self):
        displayio.release_displays()
        i2c = board.I2C()
        display_bus = displayio.I2CDisplay(i2c, device_address=0x3c)
        self.display = adafruit_displayio_ssd1306.SSD1306(display_bus, width=128, height=32)

    def text(self, str):
        # display string s
        text_area = label.Label(terminalio.FONT, text=str, color=0x00FF00)
        text_area.x = 0
        text_area.y = 10
        self.display.show(text_area)


# main program: read and display weight in infinite loop

from board import A3, D5

scale = Scale(A3)
tare_button = Button(D5, press=scale.tare)
text_display = TextDisplay()

while True:
    tare_button.poll()
    text_display.text("Weight: {:9.0f} g".format(scale.weight()))