go-and-stop.py

   1 # -*- coding: utf-8 -*-
   2 """Run the car and stop if distance to obstacle is < 40cm."""
   3 from _thread import start_new_thread
   4 from machine import Pin, PWM
   5 from utime import sleep_us, ticks_us
   6
   7 TRIG = Pin(5, Pin.OUT)
   8 ECHO = Pin(4, Pin.IN)
   9 SPEED = PWM(Pin(12), freq=1000)
  10
  11 dist = 4
  12
  13 def get_dist():
  14     """Read data from ultrasonic sensor."""
  15     global dist
  16     nc = ticks_us()
  17     while True:
  18         TRIG.off()
  19         sleep_us(2)
  20         TRIG.on()
  21         sleep_us(10)
  22         TRIG.off()
  23         while ECHO.value() == 0:
  24             pass
  25         t1 = ticks_us()
  26         while ECHO.value() == 1:
  27             pass
  28         t2 = ticks_us()
  29         dist = (t2 - t1) / 58.0
  30         nc += 20000
  31         sleep_us(nc - ticks_us())
  32     return
  33
  34 def set_speed():
  35     """Set PWM to control car speed."""
  36     nc = ticks_us()
  37     while True:
  38         if dist < 20:
  39             SPEED.duty(1023)
  40         else:
  41             SPEED.duty(0)
  42         nc += 200000
  43         sleep_us(nc - ticks_us())
  44     return
  45
  46 if __name__ == "__main__":
  47     start_new_thread(get_dist, ())
  48     start_new_thread(set_speed, ())
  49     while True:
  50         pass