3

It's my understanding that if a switch is wired to ground and the other to a GPIO pin you need a pull-up on the GPIO. Then the GPIO will usually read high and will usually read low when the switch is closed.

GPIO.setmode(GPIO.BCM)
GPIO.setup(16, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.input(16)

However, this appears to be the opposite for me. Using the code above my button, (connected to ground and GPIO 16) reads True/1 when pushed/pressed, why?

This is the button I'm using:

push to release button

  • Is it a latching button? – joan Dec 13 '17 at 21:18
  • Do you mean it reads false when released and true when pressed? BTW a picture of a button is useless. If you have the part number or datasheet we can see if its a Normally-Open (NO) or Normally Closed (NC) Switch. No way to tell from a picture – crasic Dec 13 '17 at 21:27
  • @crasic sorry my question is a little dumb and I realise that a picture does not help. Indeed, it reads 1 when pressed down and 0 when released. Should I assume that this is an always closed switch then (in release state)? would that be why? – MrKnotts Dec 13 '17 at 22:06
  • @MrKnotts it's just a common option/variety of switch that is for sale. I have added an answer that will hopefully clear stuff up. – crasic Dec 13 '17 at 23:23
3

Switches, relays, etc. come in Normally Closed (NC) or Normally Open (NO) varieties,

enter image description here

You can easily check which one you have with a multimeter.

Many Switches come in both varieties and you choses when you order, its just a matter of electrical need, sometimes you need NO sometimes NC, if you want to know why this would matter I suggest asking another question here or on electronics.stackexchange.com .

However, all is not lost. You have the flexibility of inverting your logic, you may do this in code

read_value = !read_value

or you can do this in hardware

PU -> PD
Switch to 0V -> Switch to 3V3

And from your software POV it would be what you expect the value (1 when released 0 when pressed)

  • 1
    Both of those switch actions are described as momentary in that the change in connections that result in holding your mitt on the button is undone when you remove it - as well as the NO and NC descriptions they can also be described as OFF-(ON) and ON-(OFF) with the bracketed state being the momentary one... – SlySven Dec 14 '17 at 1:02

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