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  • rasberry_pi_3_b_plus
  • raspberry_pi
Related

Crosstalk between raspberry Pi GPIO inputs

colporteur
colporteur over 6 years ago

Are there any known issues of crosstalk between GPIO inputs?

 

I am using Python module RPi.GPIO to event detect on GPIO pins. One program monitors GPIO 2 pin 3 and the second program monitors GPIO 3 pin 5. I am using GPIO.event_detected to detect events within the programs. In the GPIO 2 monitor program, when  GPIO 2 is pulled low, I get a trigger event for GPIO 2 and GPIO 3. In the GPIO 3 monitor program, when  GPIO 3 is pulled low, I get a trigger event for GPIO 3 and GPIO 2.

 

I have seen this pattern of across three different Pi's. On two of Pi's the crosstalk is across GPIO 2, 3 & 4. After obtaining the same results across a Pi 2 & Pi 3, I opened a new Pi 3B+ never used and got similar results.

 

I am using the python script below substituting the pin 3 & pin 5.

 

# setup GPIO
GPIO.setwarnings(False)

GPIO.setmode(GPIO.BOARD)  # set option to reference physical pins
# Set GPIO function
GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_UP)  # set GPIO input
GPIO.add_event_detect(5, GPIO.BOTH)

try:

   while True:

   if GPIO.event_detected(5):

   print("5 Triggered")

 

except KeyboardInterrupt:  # if ctrl+c pressed exit cleanly
   GPIO.cleanup()

except:  # this catches ALL other exceptions including errors.
   GPIO.cleanup()

finally:  # cleanup GPIO on normal exit
   GPIO.cleanup()

 

My test cases target the suggestion, I have a bad Pi(s). I have extended this same test to three new Pi 3B+ just removed from the package and get the same results. All show crosstalk between GPIO 2,3  with some being GPIO 2, 3 & 4. This suggests I am at fault and not the Pi's.

 

Can anyone share their insight?

 

Sean

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  • DAB
    DAB over 6 years ago

    Hi Sean,

     

    I too have seen some interesting behavior with Rpi I/O lines.

    I found that the tristate outputs can vary all over the place unless you either pull them up or pull them down to make sure of where they begin.

    Clearly I suggest that you always use some sort of termination on the pins you use. Do not assume they are at a stable voltage, they will not be what you expect.

     

    DAB

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  • DAB
    DAB over 6 years ago

    Hi Sean,

     

    I too have seen some interesting behavior with Rpi I/O lines.

    I found that the tristate outputs can vary all over the place unless you either pull them up or pull them down to make sure of where they begin.

    Clearly I suggest that you always use some sort of termination on the pins you use. Do not assume they are at a stable voltage, they will not be what you expect.

     

    DAB

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