go_and_stop.py

   1 # -*- coding: utf-8 -*-
   2 """Run the car and stop if distance to obstacle is < 40cm."""
   3 from machine import Pin, PWM
   4 from utime import sleep_us, ticks_us
   5
   6 TRIG = Pin(5, Pin.OUT)
   7 ECHO = Pin(4, Pin.IN)
   8 SPEED = PWM(Pin(14), freq=1000)
   9 BACK = PWM(Pin(15), freq=1000)
  10
  11 dist = 40
  12
  13 def go():
  14     """Read data from ultrasonic sensor and drive car if no obstacle."""
  15     global dist
  16     BACK.duty(0)
  17     nc = ticks_us()
  18     while True:
  19         # read sensor data
  20         TRIG.off()
  21         sleep_us(2)
  22         TRIG.on()
  23         sleep_us(10)
  24         TRIG.off()
  25         while ECHO.value() == 0:
  26             pass
  27         t1 = ticks_us()
  28         while ECHO.value() == 1:
  29             pass
  30         t2 = ticks_us()
  31         dist = (t2 - t1) / 58.0
  32         # drive if obstacle-free
  33         if dist > 10:
  34             SPEED.duty(1023)
  35         else:
  36             SPEED.duty(0)
  37         nc += 20000
  38         sleep_us(nc - ticks_us())
  39     return
  40
  41 if __name__ == "__main__":
  42     go()