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Completely new in the Raspberry Pi community, so please excuse me if this is a total noob question.

Model: Raspberry Pi 4 Model B

Component: Adafruit PIR motion sensor

I am currently following the following a simplified tutorial to hook up a PIR sensor using a 40 pin cobbler plus and breadboard: https://learn.adafruit.com/adafruits-raspberry-pi-lesson-12-sensing-movement/hardware

I have simplified it to exclude the verify the PIR sensor value and then print out "PIR ALARM!" What ends up happening when I run the code is, even when no motion is detected, the pir_sensor value in the code below is returning true.

I have adjusted both the time and sensitivity switches on the PIR sensor, but to no avail. What could I be getting wrong here?

Here is the code:

import time
import board
import digitalio

# set up motion sensor
pir_sensor = digitalio.DigitalInOut(board.D18)
pir_sensor.direction = digitalio.Direction.INPUT


while True:

    if pir_sensor.value:
        print("PIR ALARM!")

    time.sleep(0.5)

And here is my setup with the PIR sensor to my breadboard: board layout PIR sensor

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    Ah I had the same problem the first time I played PIR stuff, a couple of years ago. I found the problem very interesting and so I started my PBL (Problem Based Learning), googling wildly. I have read over ten tutorials, including Lady Ada in 2013, and the Shanghai scientists and engineers who developed the first generation of PIR. I was very impressed by the very detailed explanation of the physics principles and the engineering design and practice in making the product. I spent perhaps 20 hours experimenting the couple of different versions of PIR and finally solved the problem, to cont.
    – tlfong01
    Commented Apr 30, 2020 at 3:19
  • 1
    I am very slow in using broken English to tell my long PIR story. But I did spend another couple of hours explaining in this and other forums what I found was the cause causing fake alarm and how I verify my hypothesis, using a rice bowl. You might like to search this forum for my rice bowl post. Happy learning. Cheers.
    – tlfong01
    Commented Apr 30, 2020 at 3:25

1 Answer 1

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There are too many potential problems with the set up.

First of all you need to confirm your cobbler is correctly attached to the Pi and the breadboard.

Using a volt meter do you read 3V3 between a 3V3 column and a ground column on the breadboard?

Do you read 5V between a 5V column and a ground column on the breadboard?

If so try connecting the pin 18 column to a 3V3 column and then a ground column.

Does your software report the change?

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  • It sounds a bit like I need to take a step back and dig a bit more into the fundamentals first. I will perform the suggested testing and report back!
    – KPM
    Commented Apr 30, 2020 at 13:35

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