3. Mileage Calculation

With the ability to calculate speed, counting miles is really a piece of cake.

In this case, the mileage is calculated by multiplying the total number of revolutions by the circumference of the wheel.

from machine import Timer, Pin
import math

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

def on_left(ch):
    global left_count
    left_count += 1

def on_right(ch):
    global right_count
    right_count += 1

def on_timer(ch):
    global left_count,right_count, total_count
    # mileage
    total_count += left_count + right_count
    mileage = total_count /20.0/2 *WP
    # revolutions per second
    rps = (left_count + right_count) * 1000 /duration /20.0 /2
    # speed
    speed = rps * WP
    # clear count
    left_count = 0
    right_count = 0
    print("mileage(cm): ",mileage," ; speed(cm/s): ",speed)

# Interrupter, used to count
left_count = 0
right_count = 0
total_count = 0
left_pin = Pin(8, Pin.IN, Pin.PULL_UP)
left_pin.irq(trigger=Pin.IRQ_FALLING, handler=on_left)
right_pin = Pin(9, Pin.IN, Pin.PULL_UP)
right_pin.irq(trigger=Pin.IRQ_FALLING, handler=on_right)

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

# motor run
import motors
import time

try:
    while True:
        for i in range(20,100,10):
            motors.move("forward",i)
            time.sleep(1)
finally:
    motors.stop()
    time.sleep(0.2)

Copy the above code into Thonny or open the speed_3_get_mileage.py under the path of pico_4wd_car-v2.0\examples\learn_modules. Then click the button or press F5 to run it.

After powering up the Pico 4WD car, you can see that the speed keeps cycling between high and low, and Mileage keeps adding up unless you click to stop the script from running.