#181 wait_for_edge() not working when running program second time.

[Ivo]

I might have come accross an issue with the wait_for_edge function. I used the following project as basis, but changed it to use the wait_for_edge() function: https://tutorials-raspberrypi.com/raspberry-pi-ultrasonic-sensor-hc-sr04/

It seem to work, but only the first time. If I run the code the second time, it always fails. If I run it a third time, it works again. The funny part is, when I remove the GPIO.cleanup(), it always works! Am I doing somehting wrong or could this be an issue with RPi.GPIO? Below my code and the output from 2 runs in a row:

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#! /usr/bin/python3 import RPi.GPIO as GPIO import time GPIO.setmode(GPIO.BCM) GPIO.setwarnings(True) TRIG = 23 ECHO = 24 GPIO.setup(TRIG,GPIO.OUT) GPIO.setup(ECHO,GPIO.IN) GPIO.output(TRIG, False) print(‘Waiting a few seconds for the sensor to settle’) time.sleep(2) GPIO.output(TRIG, True) time.sleep(0.00001) GPIO.output(TRIG, False) channel = GPIO.wait_for_edge(ECHO, GPIO.RISING, timeout=5000) if channel is None: print(‘Timeout occured, echo never started’) else: pulse_start = time.time() channel = GPIO.wait_for_edge(ECHO, GPIO.FALLING, timeout=5000) if channel is None: print(‘Timeout occured, echo never stopped’) else: pulse_end = time.time() pulse_duration = pulse_end – pulse_start distance = pulse_duration * 17165 distance = round(distance, 1) print (‘Distance first time: ‘, distance, ‘in cm’) GPIO.cleanup()

Output from running the code:
>>> %Run Measure_Distance_Using_Ultra_Sound_HC-SR04_version2.py
Waiting a few seconds for the sensor to settle
Distance first time: 12.1 in cm
>>> %Run Measure_Distance_Using_Ultra_Sound_HC-SR04_version2.py
Waiting a few seconds for the sensor to settle
Timeout occured, echo never started
Timeout occured, echo never stopped
Traceback (most recent call last):
File “/home/pi/Measure_Distance_Using_Ultra_Sound_HC-SR04_version2.py”, line 35, in
pulse_duration = pulse_end – pulse_start
NameError: name ‘pulse_end’ is not defined