Raspberry-pi gpio input not stable

1
votes

I have a strange problem with raspberry (3B) ang GPIO as Input. I'm actually just experimenting and trying to get a pushbutton press without side effects.

setup

Hardware

  • PIN 16 (GPIO 26) as IN
  • PIN 6 as GND
  • 2 open Jumper wires on the pins for better debugging. Later there will be pushbutton behind

Software

  • Raspbian 9.4 stretch
  • Kernel 4.9.80-v7+ (newest over normal apt-get)
  • RPi.GPIO version 0.63

code

#!/usr/bin/python
import RPi.GPIO as GPIO
from time import sleep

red_channel = 23

GPIO.setmode(GPIO.BCM)
GPIO.setup(red_channel, GPIO.IN, pull_up_down=GPIO.PUD_UP) # pin is up to 3.3V

try:
    while True:
        state = GPIO.input(red_channel)
        if state == 0: # when pin pulled down
            print 'red pressed', state
        sleep(0.3)
except KeyboardInterrupt:
    GPIO.cleanup()

Problem

When I run the code and only come with my hand in the near of the jumper wires or even move them, button pressure will be detected. And at this point I don't get why! Did I get something wrong?

Solutions already tried

  • new wires
  • other ports
  • other raspberry (same version)!
  • OS new installed and GPIO Libs fresh installed
  • Breadboard between (same effect)

Thanks for your help!

1
pythonbuttonraspberry-pigpiobounce
Your if state == 0: print 'red pressed' is going to print it is pressed when the button is not pressed since GPIO.input(red_channel) will return False only then, was this a typo in the code? – nj2237
With this code, you will be getting output red pressed every 0.3 seconds without pressing the button – nj2237
Because the pin is set up to be up when the button will be pressed it will be pulled down (to GND). In this case GPIO.input(red_channel) will offer a 1 as long pin is up. When button pressed, pin will get pulled down and 0 will be returned. an example: razzpisampler.oreilly.com/ch07.html – Marios
oh yeah, you are right. my bad! then, this is a very weird behavior indeed. is there any pattern in the output? in the frequency of printing state True or False? – nj2237
The script will return 0 as long I move the wire. Fun fact: I inverted the wiring so that the pin is down and will be shorten to 3.3V when button pressed. Same issue. Strange – Marios

1 Answers

0
votes

I can't help thinking that you've got a short or dodgy link in this somewhere.

I'd take off the PI, and test the board with a multi-meter in continuity mode. Check what happens when you wiggle the cables etc.

Any short or wrong link should then show up as long as you test logically