029 - MicroPython TechNotes: HC-SR04 Ultrasonic Sensor

 1# More details can be found in TechToTinker.blogspot.com 
 2# George Bantique | tech.to.tinker@gmail.com
 3
 4from machine import Pin
 5from machine import Timer
 6from hcsr04 import HCSR04
 7
 8ultrasonic = HCSR04(trigger_pin=21, echo_pin=22, echo_timeout_us=1000000)
 9
10def timer0_callback(timer):
11    print('Distance: {}cm'.format(ultrasonic.distance_cm()))
12    #print('Distance: {}mm'.format(ultrasonic.distance_mm()))
13    #print('Distance: {}inch'.format(ultrasonic.distance_cm()/2.54))
14
15timer0 = Timer(0)
16timer0.init(period=500, mode=Timer.PERIODIC, callback=timer0_callback)

 1# More details can be found in TechToTinker.blogspot.com   
 2 # George Bantique | tech.to.tinker@gmail.com  
 3 from machine import Pin  
 4 from hcsr04 import HCSR04  
 5 from time import sleep_ms  
 6 ultrasonic = HCSR04(trigger_pin=21, echo_pin=22, echo_timeout_us=1000000)  
 7 led = Pin(2, Pin.OUT)  
 8 while True:  
 9   distance = ultrasonic.distance_cm()  
10   print('Distance:', distance, 'cm')  
11   if distance <= 10:  
12     print('ALERT! Intruder detected.')  
13     led.value(not led.value())  
14   else:  
15     led.value(0)  
16   sleep_ms(500)  

 1import machine, time
 2from machine import Pin
 3
 4__version__ = '0.2.0'
 5__author__ = 'Roberto Sánchez'
 6__license__ = "Apache License 2.0. https://www.apache.org/licenses/LICENSE-2.0"
 7
 8class HCSR04:
 9    """
10    Driver to use the untrasonic sensor HC-SR04.
11    The sensor range is between 2cm and 4m.
12    The timeouts received listening to echo pin are converted to OSError('Out of range')
13    """
14    # echo_timeout_us is based in chip range limit (400cm)
15    def __init__(self, trigger_pin, echo_pin, echo_timeout_us=500*2*30):
16        """
17        trigger_pin: Output pin to send pulses
18        echo_pin: Readonly pin to measure the distance. The pin should be protected with 1k resistor
19        echo_timeout_us: Timeout in microseconds to listen to echo pin. 
20        By default is based in sensor limit range (4m)
21        """
22        self.echo_timeout_us = echo_timeout_us
23        # Init trigger pin (out)
24        self.trigger = Pin(trigger_pin, mode=Pin.OUT, pull=None)
25        self.trigger.value(0)
26
27        # Init echo pin (in)
28        self.echo = Pin(echo_pin, mode=Pin.IN, pull=None)
29
30    def _send_pulse_and_wait(self):
31        """
32        Send the pulse to trigger and listen on echo pin.
33        We use the method `machine.time_pulse_us()` to get the microseconds until the echo is received.
34        """
35        self.trigger.value(0) # Stabilize the sensor
36        time.sleep_us(5)
37        self.trigger.value(1)
38        # Send a 10us pulse.
39        time.sleep_us(10)
40        self.trigger.value(0)
41        try:
42            pulse_time = machine.time_pulse_us(self.echo, 1, self.echo_timeout_us)
43            return pulse_time
44        except OSError as ex:
45            if ex.args[0] == 110: # 110 = ETIMEDOUT
46                raise OSError('Out of range')
47            raise ex
48
49    def distance_mm(self):
50        """
51        Get the distance in milimeters without floating point operations.
52        """
53        pulse_time = self._send_pulse_and_wait()
54
55        # To calculate the distance we get the pulse_time and divide it by 2 
56        # (the pulse walk the distance twice) and by 29.1 becasue
57        # the sound speed on air (343.2 m/s), that It's equivalent to
58        # 0.34320 mm/us that is 1mm each 2.91us
59        # pulse_time // 2 // 2.91 -> pulse_time // 5.82 -> pulse_time * 100 // 582 
60        mm = pulse_time * 100 // 582
61        return mm
62
63    def distance_cm(self):
64        """
65        Get the distance in centimeters with floating point operations.
66        It returns a float
67        """
68        pulse_time = self._send_pulse_and_wait()
69
70        # To calculate the distance we get the pulse_time and divide it by 2 
71        # (the pulse walk the distance twice) and by 29.1 becasue
72        # the sound speed on air (343.2 m/s), that It's equivalent to
73        # 0.034320 cm/us that is 1cm each 29.1us
74        cms = (pulse_time / 2) / 29.1
75        return cms