peter pan peter pan - 1 year ago 145
Python Question

2 PIR motion sensors to detect human presence

I'm having trouble programming the logic of 2 PIR sensors to print a message in console whenever a user place both hands on the PIR sensors.I have managed to successfully attach the PIR sensors to the raspberry pi using GPIO,GND and 5v port. The code that I currently have does print out a message in console whenever someone waves there hand across one but i'm having difficulty modifying the code to print an error message out when someone waves their hand on both the PIR sensors.

We can read input from the sensor using GP4 and GP17

import RPi.GPIO as GPIO
import time

sensor = 4
sensor2 = 17
GPIO.setup(sensor, GPIO.IN, GPIO.PUD_DOWN)

previous_state = False
current_state = False

while True:
previous_state = current_state
current_state = GPIO.input(sensor)
if current_state(TRUE) != previous_state(FALSE):
new_state = "HIGH" if current_state else "LOW"
print("GPIO pin %s is %s" % (sensor, new_state))

The program is pretty simple. 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. The pin continually check for any changes, uses a while True loop for this. This is an infinite loop so the program will run continuously unless we stop it manually with Ctrl + C.

Then use two Boolean variables (True or False) 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.

jDo jDo
Answer Source

I haven't checked the code for syntax errors and don't have access to a Pi at the moment, but it's an example of what I was referring to in this comment:

"Use RPi.GPIO's add_event_detect interrupt driven callbacks instead. Then you can eliminate the infinite loop entirely and let the script do other stuff while still reacting to the sensors. You can use the time difference between rising edges to define what "simultaneously" means to you (a max difference of 1 second between sensor 1 and sensor 2 being triggered, for instance)"

import RPi.GPIO as GPIO
import time


# change GPIO.RISING to GPIO.FALIING if your PIRs are active low 
GPIO.add_event_detect(17, GPIO.RISING, callback=callback_func)
GPIO.add_event_detect(4, GPIO.RISING, callback=callback_func)

pir1_last = pir2_last = time.time()

def callback_func(pin):
    global pir1_last
    global pir2_last

    if GPIO.input(17):
        pir1_last = time.time()
    if GPIO.input(4):
        pir2_last = time.time()

    t_diff = abs(pir1_last - pir2_last)
    if t_diff < 0.5:
        print "it's been less than 0.5 seconds since both PIRs were activated"

def main():
    while True:
        print "Not blocking! You're free to do other stuff here"
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