I want to use a slider button of 3 pins.

Actually I'm using 2 of it, like the schematic below:


simulate this circuit – Schematic created using CircuitLab

My code is:

import RPi.GPIO as GPIO
green_led = 21
GPIO.setup(green_led, GPIO.IN)

while True:
    green_led_state = GPIO.input(green_led)
    print('#### - ',green_led_state, ' - ####')

In my opinion whith this code, if don't touch my slider always have to print the same value (1 or 0) depending of its position. And if I change the position of the slider, print the other value all the time.

But now, without touching nothing is printing 0 and 1 randomly (I think randomly). Why this? Why some times has current and sometimes not?


  • Like your earlier question, you are connecting LEDs without a current limiting resistor. You are lucky not to have blown something up, but excessive current will eventually cause problems. – Milliways May 25 '19 at 23:34
  • Sorry I didn't put in the schematic but it is in my real circuit :) – Lleims May 26 '19 at 9:00

A GPIO set as an input will float (read randomly low/high) until a voltage is applied.

The simplest thing to do is set the internal resistor pulls to the opposite of the value set by the switch. If I read your circuit correctly use

GPIO.setup(green_led, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

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