49 lines
1.9 KiB
Python
49 lines
1.9 KiB
Python
import machine, time
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from machine import Pin
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# From https://github.com/udacity/cd13765-deci-emb-sys-l4-term2-project.git
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class HCSR04:
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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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time.sleep_us(5)
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self.trigger.value(1)
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# Send a 10us pulse.
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time.sleep_us(10)
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self.trigger.value(0)
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try:
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pulse_time = machine.time_pulse_us(self.echo, 1, self.echo_timeout_us)
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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_cm(self):
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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 = int((pulse_time / 2) // 29.1)
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return cms
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