82 lines
3.3 KiB
Python
82 lines
3.3 KiB
Python
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from machine import Pin, time_pulse_us
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from utime import sleep_us
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__version__ = '0.2.1'
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__author__ = 'Roberto Sánchez'
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__license__ = "Apache License 2.0. https://www.apache.org/licenses/LICENSE-2.0"
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class HCSR04:
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"""
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Driver to use the untrasonic sensor HC-SR04.
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The sensor range is between 2cm and 4m.
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The timeouts received listening to echo pin are converted to OSError('Out of range')
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"""
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# echo_timeout_us is based in chip range limit (400cm)
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def __init__(self, trigger_pin, echo_pin, echo_timeout_us=500*2*30):
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"""
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trigger_pin: Output pin to send pulses
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echo_pin: Readonly pin to measure the distance. The pin should be protected with 1k resistor
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echo_timeout_us: Timeout in microseconds to listen to echo pin.
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By default is based in sensor limit range (4m)
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"""
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self.echo_timeout_us = echo_timeout_us
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# Init trigger pin (out)
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self.trigger = Pin(trigger_pin, mode=Pin.OUT, pull=None)
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self.trigger.value(0)
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# Init echo pin (in)
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self.echo = Pin(echo_pin, mode=Pin.IN, pull=None)
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def _send_pulse_and_wait(self):
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"""
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Send the pulse to trigger and listen on echo pin.
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We use the method `machine.time_pulse_us()` to get the microseconds until the echo is received.
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"""
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self.trigger.value(0) # Stabilize the sensor
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sleep_us(5)
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self.trigger.value(1)
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# Send a 10us pulse.
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sleep_us(10)
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self.trigger.value(0)
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try:
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pulse_time = time_pulse_us(self.echo, 1, self.echo_timeout_us)
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# time_pulse_us returns -2 if there was timeout waiting for condition; and -1 if there was timeout during the main measurement. It DOES NOT raise an exception
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# ...as of MicroPython 1.17: http://docs.micropython.org/en/v1.17/library/machine.html#machine.time_pulse_us
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if pulse_time < 0:
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MAX_RANGE_IN_CM = const(500) # it's really ~400 but I've read people say they see it working up to ~460
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pulse_time = int(MAX_RANGE_IN_CM * 29.1) # 1cm each 29.1us
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return pulse_time
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except OSError as ex:
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if ex.args[0] == 110: # 110 = ETIMEDOUT
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raise OSError('Out of range')
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raise ex
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def distance_mm(self):
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"""
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Get the distance in milimeters without floating point operations.
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"""
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pulse_time = self._send_pulse_and_wait()
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# To calculate the distance we get the pulse_time and divide it by 2
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# (the pulse walk the distance twice) and by 29.1 becasue
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# the sound speed on air (343.2 m/s), that It's equivalent to
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# 0.34320 mm/us that is 1mm each 2.91us
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# pulse_time // 2 // 2.91 -> pulse_time // 5.82 -> pulse_time * 100 // 582
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mm = pulse_time * 100 // 582
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return mm
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def distance_cm(self):
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"""
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Get the distance in centimeters with floating point operations.
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It returns a float
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"""
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pulse_time = self._send_pulse_and_wait()
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# To calculate the distance we get the pulse_time and divide it by 2
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# (the pulse walk the distance twice) and by 29.1 becasue
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# the sound speed on air (343.2 m/s), that It's equivalent to
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# 0.034320 cm/us that is 1cm each 29.1us
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cms = (pulse_time / 2) / 29.1
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return cms
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