HC-SR04 Sensor driver in micropython

Micropython driver for the well-known untrasonic sensor HC-SR04

The driver has been tested on Wemos D1 mini PRO and ESP8266 12e, but It should work on whatever other micropython board, if anyone find problems in other boards, please open an issue and we'll see.

Motivation

Using the more accurate method machine.time_pulse_us() that is compliant with "standard" micropython, there is no code for specific boards.

The distance_mm() don't use floating point operations, for environments where there is no floating point capabilities.

Breaking changes:

This fork is an extension of the original driver which now take into account the room temperature, check the author's work. The new constructor is:

from hcsr04 import HCSR04

sensor = HCSR04(trigger_pin=16, echo_pin=0, echo_timeout_us=500*2*30, air_temp=20)

This is a patch for micropython version 1.9.x and 1.10 for the method machine.time_pulse_us() which doesn't raise an OSError with ETIMEDOUT anymore, but it has a few more return conditions. In this patch no timeouts exceptions are raised, a mathematical inf approach is preferred, so error management is left to the user.

Examples of use:

How to get the distance

The distance_cm() method returns a float with the distance measured by the sensor.

from hcsr04 import HCSR04

sensor = HCSR04(trigger_pin=16, echo_pin=0)

distance = sensor.distance_cm()

print('Distance:', distance, 'cm')

There is another method, distance_mm(), that returns the distance in milimeters (int type) and no floating point is used, designed for environments that doesn't support floating point operations.

distance = sensor.distance_mm()

print('Distance:', distance, 'mm')

The default timeout is based on the sensor limit (4m), but we can also define a different timeout, passing the new value in microseconds to the constructor.

from hcsr04 import HCSR04

sensor = HCSR04(trigger_pin=16, echo_pin=0, echo_timeout_us=1000000)

distance = sensor.distance_cm()

print('Distance:', distance, 'cm')

Error management

When the driver reaches the timeout while is listening the echo pin, a inf value is returned. The error management is handled by the user, for example:

from hcsr04 import HCSR04
from math import isinf

sensor = HCSR04(trigger_pin=16, echo_pin=0)

distance = sensor.distance_cm()
if isinf(distance):
	print("Too far...")
else:
	print('Distance:', distance, 'cm')