Raspberry Pi GPIO input help

Question

I have this rocker switch.

I have it connected on the GND pin to GPIO pin 11 (BCM 17) and a 1 kohm resistor to GND on the Raspberry Pi, the 3.3 V pin from the Raspberry Pi to positive:

Switch '+' -> 3.3 V
Switch '-' -> GPIO ALSO to resistor and then GND of the Raspberry Pi.

I have this code:

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BOARD)
GPIO.setup(11, GPIO.IN)

while True:
    if(GPIO.input(11) == True):
            print("switch ON")
    else:
            print("switch OFF")

But it only ever says that it's off. Why is this?

Answer 1

I don't know why your switch doesn't appear to work. The usual reason is it's not connected to the gpio you are using in software.

I think setting up BOARD numbering will use the P1 pin numbers. So when you refer to 11 you are referring to P1-11 (which is attached to Broadcom gpio 17).

http://elinux.org/RPi_Low-level_peripherals

Personally I'd wire the switch as follows

Pi ground - resistor - switch - gpio

and set the internal pull-up on the gpio to 3.3V.

The resistor acts as a safety device in case the gpio is accidentally set as a high output. Without a resistor there would be a short to ground and the gpio might be damaged.

Any resistor in the range 300-10,000 ohm should be fine.

With the above set-up the gpio will read 1 if the switch is open and 0 if closed.

Answer 2

In the schematic (borrowed) you can see GND is connected to the GPIO. This provides a LOW state which means the switch is OPEN. When you close the switch the GPIO will read high. The resistor is 10 kohm, but 1 kohm is also OK. That value only matters if you are trying to save battery power.

Make sure to use 3.3 volt and not 5 volt.

Answer 3

Thanks for all the help!

In the end, I tried this which works.

 Black is gnd of Pi
 Green is GPIO input pin
 Red is 3v3 pin of Pi

Is this safe?