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Content import machine, time from machine import Pin __version__ = '0.2.0' __author__ = 'Roberto Sánchez' __license__ = "Apache License 2.0. https://www.apache.org/licenses/LICENSE-2.0" class HCSR04: """ Driver to use the untrasonic sensor HC-SR04. The sensor range is between 2cm and 4m. The timeouts received listening to echo pin are converted to OSError('Out of range') """ # echo_timeout_us is based in chip range limit (400cm) def __init__(self, trigger_pin, echo_pin, echo_timeout_us=500*2*30): """ trigger_pin: Output pin to send pulses echo_pin: Readonly pin to measure the distance. The pin should be protected with 1k resistor echo_timeout_us: Timeout in microseconds to listen to echo pin. By default is based in sensor limit range (4m) """ self.echo_timeout_us = echo_timeout_us # Init trigger pin (out) self.trigger = Pin(trigger_pin, mode=Pin.OUT, pull=None) self.trigger.value(0) # Init echo pin (in) self.echo = Pin(echo_pin, mode=Pin.IN, pull=None) def _send_pulse_and_wait(self): """ Send the pulse to trigger and listen on echo pin. We use the method `machine.time_pulse_us()` to get the microseconds until the echo is received. """ self.trigger.value(0) # Stabilize the sensor time.sleep_us(5) self.trigger.value(1) # Send a 10us pulse. time.sleep_us(10) self.trigger.value(0) try: pulse_time = machine.time_pulse_us(self.echo, 1, self.echo_timeout_us) return pulse_time except OSError as ex: if ex.args[0] == 110: # 110 = ETIMEDOUT raise OSError('Out of range') raise ex def distance_mm(self): """ Get the distance in milimeters without floating point operations. """ pulse_time = self._send_pulse_and_wait() # To calculate the distance we get the pulse_time and divide it by 2 # (the pulse walk the distance twice) and by 29.1 becasue # the sound speed on air (343.2 m/s), that It's equivalent to # 0.34320 mm/us that is 1mm each 2.91us # pulse_time // 2 // 2.91 -> pulse_time // 5.82 -> pulse_time * 100 // 582 mm = pulse_time * 100 // 582 return mm def distance_cm(self): """ Get the distance in centimeters with floating point operations. It returns a float """ pulse_time = self._send_pulse_and_wait() # To calculate the distance we get the pulse_time and divide it by 2 # (the pulse walk the distance twice) and by 29.1 becasue # the sound speed on air (343.2 m/s), that It's equivalent to # 0.034320 cm/us that is 1cm each 29.1us cms = (pulse_time / 2) / 29.1 return cms