PIR Motion Sensor

This isn't a project so much as my attempts to remove false positive motion events when trying to use this PIR in a smart doorbell.

There seem to be three things that trigger motion detection:

• High CPU Usage

• High Wi-Fi Traffic

• Motion

I really only want the last to trigger motion.

I had no idea what was causing the false positives. So, I started googling. Many people seem to have issues with PIR sensors. As expected, many of the most promising fixes were from stackoverflow.com or raspberrypi.org.

My approach with each suggested fix was to add it, reboot the RPi, and let it run for 4-12 hours while collecting all motion detection messages.

If the number of false positives decreased, then I would keep the change. If there was no significant decrease, then it goes into the failed category.

Before looking for a fix, I checked for hourly jobs, such as, cron, systemd and so on. There doesn't seem to be anything running that corresponds with the false positive motion detection except perhaps HRNG, which is hardware random number generator.

Worked

Instead of just detecting motion on the rising edge, the code below waits a few seconds and then checks if the motion pin is still high.

• High CPU or Wi-Fi usage still triggers motion detection

Failed

Things that were tried, and failed to make any difference in my system. Failing in my system, doesn't mean it won't work in yours. By failing, I mean running this command every couple of secondsf or about 10 seconds: cat /var/log/syslog

Putting aluminum foil grounded and wrapped in electrical tape around

• PIR

• Wires from PIR to GPIO pins

• I tried grounded and ungrounded. Grounding made false positives more common, which makes no sense

Disable Bluetooth by adding a line to the file:

$ sudo nano /boot/config.txt

dtoverlay=disable-bt

Disable Bluetooth by adding two lines to the file:

$ sudo nano /etc/modprobe.d/raspi-blacklist.conf

blacklist btbcm

blacklist hci_uart

Put 10K Ohm resistor between GND and PIR GPIO pin. I didn't solder this. It seemed to reduce false positives at first and then went back to a false positive once every two hours. It might have slipped loose.

Disabling motion detection after coming out of sleep didn't work

Since the PIR white plastic body extends into the case. I thought the hot glue and PIR body might be picking up heat from either the CPU or the Wi-Fi chip. So, I painted all parts of the hot glue and PIR white case with an opaque black paint. However, this failed.

One suggestion was to put Ferrite beads around or between the PIR wires to the Raspberry Pi

However, on my PIR, the board looks like it has a Ferrite bead (silver horizontal rectangle in photo above, and two on the reverse side)

I could not find small enough snap-on Ferrite beads for AWG 36 gauage wire

I put Ferrite beads in-line, and this prevented all motion from being detected

References

Adafruit PIR Motion Sensor Tutorial

ReadTheDocs 13.1.3 Motion Sensor

SourceForge Raspberry PI GPIO

PIR Motion Sensor issues

Ferrite Beads

Stack Overflow - my question

Best solution found: kapcom01 from stackoverflow and edited by Serge Stroobandt

The following is a simple python script to print a message when motion is detected.

Use the following command to create the script on the Raspberry Pi

$ nano motion.py

and cut-and-paste the following:

#!/usr/bin/env python

# Controls the motion sensor

# run using:

# sudo python motion.py

# modules

import RPi.GPIO as GPIO

import subprocess

import time

# globals

# GPIO Pins

MOTION_PIN = 17

MOTION_WAIT = 1 # 1 minute

lastMotion = datetime.datetime.now()

motionOne = False

# Disable warnings

GPIO.setwarnings(False)

# gpio MOTION pin

GPIO.setmode(GPIO.BCM)

GPIO.setup(MOTION_PIN, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

# this call back occurs when CPU or Wi-Fi usage is high

def motionCallback(self):

# attempting to determine if rising edge is actually a true event

# motion sensor trigger stays high for ~2 seconds

now = datetime.datetime.now()

tn = now.strftime("%H:%M:%S")

logging.debug('motionCallback: now = ('+ tn + ')')

time.sleep(4)

if GPIO.input(MOTION_PIN):

logging.debug('motion detected')

# threading.Timer(MOTION_DELAY, motionTextCallback).start()

sendTextMessage('motion detected')

GPIO.remove_event_detect(MOTION_PIN)

time.sleep(20)

GPIO.add_event_detect(MOTION_PIN, GPIO.RISING, callback=motionCallback, bouncetime=300)

GPIO.add_event_detect(MOTION_PIN, GPIO.RISING, callback=motionCallback, bouncetime=300)

while True:

time.sleep(3600)