test-pir-python.md

Test the PIR motion sensor in Python

We're going to use the Python programming language to write some code that will detect movement and print out some text. When movement is detected the PIR motion sensor applies power to its OUT pin, which we have connected to GPIO pin 4 on the Pi. So in our code we just need to continually check pin 4 to see if it has power or not.

If a pin has power we call it HIGH and if not we call it LOW.

The program is pretty simple. We will first set up the Raspberry Pi GPIO pins to allow us to use pin 4 as an input; it can then detect when the PIR module sends power. We need to continually check the pin for any changes, so a while True loop is used for this. This is an infinite loop so the program will run continuously unless we stop it manually with Ctrl + C.

We then use two Boolean (True or False) variables for the previous and current states of the pin, the previous state being what the current state was the preceding time around the loop. Inside the loop we compare the previous state to the current state to detect when they're different. We don't want to keep displaying a message if there has been no change.

1. Open Idle3 from the main menu.

1. Create a new program from the File -> New Window option

2. Enter the code below.

   import RPi.GPIO as GPIO
   import time
   
   sensor = 4
   
   GPIO.setmode(GPIO.BCM)
   GPIO.setup(sensor, GPIO.IN, GPIO.PUD_DOWN)
   
   previous_state = False
   current_state = False
   
   while True:
       time.sleep(0.1)
       previous_state = current_state
       current_state = GPIO.input(sensor)
       if current_state != previous_state:
           new_state = "HIGH" if current_state else "LOW"
           print("GPIO pin %s is %s" % (sensor, new_state))

3. Press Ctrl + S and enter a sensible name for the file.

4. Now run the Python file by pressing the F5 key.

5. If you start moving or waving the sensor pin will go HIGH. Keep on waving and it will stay HIGH, and it will only go back to LOW if you keep still again. If you see the sensor behave like this, then everything is working correctly. If not, something is wrong and you need to go back and troubleshoot.

   GPIO pin 4 is HIGH
   GPIO pin 4 is LOW
   GPIO pin 4 is HIGH
   

6. Press Ctrl + C when you want to exit.

7. On the PIR module, you should see two orange components with sockets that fit a Phillips screwdriver.

   

   These are called potentiometers, and they allow you to adjust the sensitivity of the sensor and the detection time. We would suggest setting the sensitivity to maximum and the time to minimum, but the choice is yours.

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