3. servo.py Module

Similarly, in order to make the code better readable when the servo is used with other components, the servo-related code is encapsulated into a library as follows.

Note

The encapsulated library servo.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 Pin, PWM
import time

def mapping(x, in_min, in_max, out_min, out_max):
    return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min

class Servo():
    MAX_PW = 2500
    MIN_PW = 500
    PERIOD = 20000

    def __init__(self, pin):
        self.servo = PWM(Pin(pin, Pin.OUT))
        self.servo.freq(50)

    def set_angle(self, angle):
        try:
            angle = int(angle)
        except:
            raise ValueError("Angle value should be int value, not %s"%angle)
        if angle < -90: # most left
            angle = -90
        if angle > 90: #most right
            angle = 90

        pulse_width=mapping(angle, -90, 90, self.MAX_PW, self.MIN_PW)
        duty=int(mapping(pulse_width, 0, self.PERIOD, 0 ,0xffff))
        self.servo.duty_u16(duty)

if __name__ == '__main__':
    servo = Servo(18)
    for i in range(0, -90, -1):
        servo.set_angle(i)
        time.sleep(0.01)
    for i in range(-90, 90, 1):
        servo.set_angle(i)
        time.sleep(0.01)
    for i in range(90, 0, -1):
        servo.set_angle(i)
        time.sleep(0.01)