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Among all the 40 GPIO pins, how many of them are available to connect a switch for on-off information?

I counted more than 24 GPIO_* connections here, but are they all available via Python?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN, pull_up_down=GPIO.PUD_UP)
if GPIO.input(17):
    ...

enter image description here

3

The 40 pin expansion header connects to 28 GPIO. They are Broadcom GPIO 0 through 27.

You are recommended not to use GPIO 0/1 as they are intended to be used by HATs.

Any recent GPIO library will give access to all the GPIO connected to the expansion header.

  • Thanks. Can GPIO 2/3 be used for an open/closed switch? it seems that no, because of the pull-up resistor (?). Is there a way to use these 2 GPIO anyway? – Basj Mar 2 '17 at 23:23
  • 1
    You can use 2 and 3 for a button switch. You could connect the other end to ground when closed. The downside is just the waste of 3V3 through 1k8, or 2mA when the switch is operated. – joan Mar 2 '17 at 23:51

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