PIR motion detection code

[luarit]

Hello,

I ma trying to do something simple, I want to test the PIR motion sensor (PIR HC-SR501) I have.

I connected to GND, Vc5 and GPIO4. I tried to run below code, but it alwasy detect motion, I dont understand why! I disconnected the sensor and I ran it again and It also detect motion event if it is not plugged any more... any idea?

Code: Select all

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.IN)
#Read output from PIR motion sensor
#GPIO.setup(3, GPIO.OUT)
#LED output pin
print "Ready"

while True:
        if GPIO.input(7):
                print "Motion Detection"
        time.sleep(1)

[joan]

GPIO4 (pin 7) has the internal pull-up enabled at power-up. It will read high unless a stronger external force sets it low. Perhaps set the internal pull-down in software?

[luarit]

Thanks Joan. Raspberry is new. What does it mean to set the internal pull down in software? And how I can do it?

[joan]

The RPi.GPIO documentation is at https://sourceforge.net/p/raspberry-gpi ... /Examples/

Basically change

Code: Select all

GPIO.setup(7, GPIO.IN)

to

Code: Select all

GPIO.setup(7, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

[boyoh]

You are given the option of setting the GPIO In/ Put impedance ( resistance ) level that the processor can respond too

In its high impedance state Floating, it will not sink or source a working level signal this being a logic level

0 low or 1 high, So you MUST set it to a working impedance ( resistance ) level by setting the internal resistance 50k

or using external resistance of 10k. If you want it to respond to a logic 1 high you connect it to the 0v rail

If you want it respond to a logic 0 low you connect it to the 3.3v rail.

One point is if you have the pull up resister to low a value this will this will set the IN/PUT impedance to low

Ok for noise suppression, but will degrade a low input signal

Regards BoyOh

[pcmanbob]

You should not need a pull down on an input if it's connected to a PIR sensor as it provides both a low output and a high output.

Have you got the 1-wire interface enabled as gpio4 ( physical pin 7 ) as that is the default pin for the 1-wire interface.

[luarit]

I also tried other GPIO as 17, 27, etc,...

[luarit]

This is how I set up everything.

Image

WhatsApp Image 2020-01-24 at 23.50.18.jpeg (73.86 KiB) Viewed 536 times

[DougieLawson]

You're very likely to burnout all of your GPIOs (one each time you experiment until your RPi dies) with a 5V PIR connected to a GPIO without a 1.8K/3.3K voltage divider.

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   PIR
   |
   |
  +-+
  | |
  | | 1.8KOhm
  +-+
   |
   +---- GPIO
   |
  +-+
  | |
  | | 3.3KOhm
  +-+
   |
   GND

[rpiMike]

That PIR has a 3.3V output:

https://thepihut.com/products/pir-infra ... r-hc-sr501

[luarit]

It doesnt look to have a problem here
https://www.freva.com/2019/05/21/hc-sr5 ... pberry-pi/

[pcmanbob]

So did you set the PIR up before you connected it to your pi ?

set the time delay pot fully anticlockwise, set the sensitivity pot to the mid position , and put the jumper on the H position for the repeated trigger mode ( see details in the link you posted ).

also check the pin layout matches your PIR as some I have seen have the +power and ground pins reversed, the +power pin should be next to the diode, highlighted yellow in the image below



Then connect your PIR like this.



and run the code in the linked site

Code: Select all

import RPi.GPIO as GPIO
import time
 
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
PIR_PIN = 23
GPIO.setup(PIR_PIN, GPIO.IN)

print('Starting up the PIR Module ')
time.sleep(1)
print ('Ready')

while True:
  if GPIO.input(PIR_PIN):
    print('Motion Detected')
  time.sleep(1)
  

once the PIR is triggered you have to leave it for a few seconds before it will stop triggering and be ready to trigger again.

[luarit]

thanks pcmanbob. It is working now. I am not sure why. I only change the Output pin GPIO23 as you said. Not sure why I cannot use the other PIN

[pcmanbob]

thanks pcmanbob. It is working now. I am not sure why. I only change the Output pin GPIO23 as you said. Not sure why I cannot use the other PIN

As I said gpio4 is the default pin for the 1-wire interface , if this is enabled it will interfere with the operation of the pin if you try to use it as a normal gpio pin.