I still do not understand exactly what you are talking about.
Is this the script where you are seeing “false positives”/incorrect output?
more /home/pi/Dexter/GrovePi/Projects/Ultrasonic_And_Relay/Ultrasonic_And_Relay.py
# GrovePi + Grove Ultrasonic Ranger
# http://www.seeedstudio.com/wiki/Grove_-_Ultrasonic_Ranger
# This is an project using the Grove Ultrasonic Ranger and Relay from GrovePi start kit
#
# In this project, the ultrasonic can figure out the distance of object in front,
# when object close to it within 10cm, the relay will turn on
'''
## License
The MIT License (MIT)
GrovePi for the Raspberry Pi: an open source platform for connecting Grove Sensors to the Rasp
berry Pi.
Copyright (C) 2017 Dexter Industries
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
'''
from grovepi import *
# Connect the Grove Ultrasonic Ranger to digital port D4
# SIG,NC,VCC,GND
ultrasonic_ranger = 4
Relay_pin = 2
pinMode(Relay_pin,"OUTPUT")
while True:
try:
# Read distance value from Ultrasonic
distant = ultrasonicRead(ultrasonic_ranger)
print(distant,'cm')
if distant <= 10:
digitalWrite(Relay_pin,1)
else:
digitalWrite(Relay_pin,0)
except TypeError:
print("Error")
except IOError:
print("Error")
By “false positives” do you mean the relay is triggered when the distance reading is not less than 10cm or the distance readings are less than 10cm when the actual distance is not less than 10cm?
That script contains no sleep to limit driving the ultrasonic ranger too fast, (perhaps the print statement is supposed to be limiting the cycle - not a good strategy, IMO)
The example in the Grove Ultrasonic Ranger datasheet shows a 0.250 second delay between readings.
You could try your script adding:
from time import sleep
...
while True:
sleep(0.250) # limit loop to allow ultrasonic sensor recovery
try:
In one of my Ultrasonic ranger test scripts (from two years ago), I see a sleep(0.100) statement, so it would appear I determined the sensor could be used to take 10 readings per second.
Personally, I think that any use of the ultrasonic ranger needs to take three readings and use the average.
The readings have a tendency to bounce around a bit, so an average over three readings, with a “sensor recovery time delay” in between each reading is a more reliable way to use a ranging sensor.