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node-red-nodes/hardware/PiSrf/nrsrf.py

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#!/usr/bin/python
# Python driver for SRF04 and SRO05 Ultrasonic sensors
# Modified to use PINS not BCM : Dave Conway-Jones
#import
import RPi.GPIO as GPIO
import time
import sys
import os, select
# Turn off warnings if you run it a second time...
GPIO.setwarnings(False)
ECHO = 0
TRIGGER = 0
OLD = 0
SLEEP = 0.5
MAX_DIST = 400
def Measure():
realstart = time.time()
GPIO.output(TRIGGER, True)
time.sleep(0.00001)
GPIO.output(TRIGGER, False)
while GPIO.input(ECHO)==0:
start = time.time()
Dif = time.time() - realstart
if Dif > 0.2:
print("Ultrasonic Sensor Timed out, Restart.")
time.sleep(0.4)
return 400
while GPIO.input(ECHO)==1:
stop = time.time()
Dif = time.time() - realstart
if Dif > 0.4:
print("Ultrasonic Sensor Timed out, Restarting.")
time.sleep(0.2)
return 400
elapsed = stop - start
distance = (elapsed * 36000)/2
return distance
# Main program loop
if len(sys.argv) > 1:
pins = sys.argv[1].lower().split(',')
if len(pins) != 3:
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print("Bad parameters supplied")
print(pins)
sys.exit(0)
TRIGGER = int(pins[0])
ECHO = int(pins[1])
SLEEP = float(pins[2])
GPIO.setmode(GPIO.BOARD) # Use GPIO BOARD numbers
GPIO.setup(TRIGGER, GPIO.OUT) # Trigger
GPIO.output(TRIGGER, False)
GPIO.setup(ECHO, GPIO.OUT) # Echo
GPIO.output(ECHO, False)
GPIO.setup(ECHO,GPIO.IN)
# Flush stdin so we start clean
while len(select.select([sys.stdin.fileno()], [], [], 0.0)[0])>0:
os.read(sys.stdin.fileno(), 4096)
while True:
try:
distance = int( Measure() + 0.5 )
if distance != OLD and distance > 2 and distance < 400:
print(distance)
OLD = distance
time.sleep(SLEEP)
except: # try to clean up on exit
print("0.0")
GPIO.cleanup()
sys.exit(0)
else:
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print("Bad params")
print(" nrsrf.py trigger_pin, echo_pin, rate_in_seconds")
sys.exit(0)