4. speed.py Module

Similarly, in order to keep the code simple and organized when using the speed module with other modules, we have encapsulated all its related code into a library.

When you use it, you just need to import this library, and you can call the functions inside directly.

get_speed()
get_mileage()

Note

The encapsulated library speed.py has been saved in pico_4wd_car-v2.0\libs, which may differ from the ones shown in the course, so please refer to the file under libs path when using it.

from machine import Timer, Pin
import math

class Speed():

    WP = 2 * math.pi * 3.3 # wheel_perimeter(cm): 2 * pi * r
    duration = 200 # ms, Timer interval

    def __init__(self, pin1, pin2):
        # value for return
        self.total_count = 0
        self.speed = 0

        # Interrupter, used to count
        self.left_count = 0
        self.right_count = 0
        self.left_pin = Pin(pin1, Pin.IN, Pin.PULL_UP)
        self.left_pin.irq(trigger=Pin.IRQ_FALLING, handler=self.on_left)
        self.right_pin = Pin(pin2, Pin.IN, Pin.PULL_UP)
        self.right_pin.irq(trigger=Pin.IRQ_FALLING, handler=self.on_right)

        # Timer, print speed
        self.tim = Timer()
        self.tim.init(period=self.duration, mode=Timer.PERIODIC, callback=self.on_timer)

    def on_left(self,ch):
        self.left_count += 1

    def on_right(self,ch):
        self.right_count += 1

    def on_timer(self,ch):
        # mileage
        self.total_count += self.left_count + self.right_count
        # revolutions per second
        rps = (self.left_count + self.right_count) * 1000 /self.duration /20.0 /2
        # speed
        self.speed = rps * self.WP
        # clear count
        self.left_count = 0
        self.right_count = 0

    def get_speed(self): # Unit: cm/s
        return self.speed

    def get_mileage(self): # Unit: m
        return self.total_count /20.0/2 * self.WP /100

    def reset_mileage(self):
        self.total_count = 0

# init
sp = Speed(8, 9)

# detect
try:
    import motors
    import time
    while True:
        for i in range(20,100):
            power = round(i / 10) * 10
            motors.move("forward",power)
            print(f'Power(%%):{power}  Speed(cm/s):{sp.get_speed():.2f} Mileage(m):{sp.get_mileage():.2f}')
            time.sleep(0.2)
finally:
    motors.stop()
    time.sleep(0.2)