# Notes

1. **BCM pin numbering**

    This library uses Broadcom (BCM) pin numbering for the GPIO pins, as
    opposed to BOARD. Unlike the `RPi.GPIO` library, this is not configurable.

    Any pin marked `GPIO` can be used for generic components.

    The BCM pin layout is as follows:

    |            |            |
    |-----------:|:-----------|
    |    3V3     | 5V         |
    |  **GPIO2** | 5V         |
    |  **GPIO3** | GND        |
    |  **GPIO4** | **GPIO14** |
    |        GND | **GPIO15** |
    | **GPIO17** | **GPIO18** |
    | **GPIO27** | GND        |
    | **GPIO22** | **GPIO23** |
    |        3V3 | **GPIO24** |
    | **GPIO10** | GND        |
    |  **GPIO9** | **GPIO25** |
    | **GPIO11** | **GPIO8**  |
    |        GND | **GPIO7**  |
    |        DNC | DNC        |
    |  **GPIO5** | GND        |
    |  **GPIO6** | **GPIO12** |
    | **GPIO13** | GND        |
    | **GPIO19** | **GPIO16** |
    | **GPIO26** | **GPIO20** |
    |        GND | **GPIO21** |

    - *GND = Ground*
    - *3V3 = 3.3 Volts*
    - *5V = 5 Volts*
    - *DNC = Do not connect (special use pins)*

2.  **Wiring**

    All components must be wired up correctly before using with this library.

3.  **Keep your program alive with `signal.pause`**

    The following program looks like it should turn an LED on:

        from gpiozero import led

        led = LED(2)
        led.on()

    And it does, if you're using the Python shell, IPython shell or IDLE shell,
    but if you saved this program as a Python file and ran it, it would flash
    on for a moment then the program would end and it would turn off.

    The following file includes an intentional `pause` to keep the program
    alive:

        from gpiozero import LED
        from signal import pause

        led = LED(2)
        led.on()
        pause()

    Now running the program will stay running, leaving the LED on, until it is
    forced to quit.

    Similarly, when setting up callbacks on button presses or other input
    devices, the program needs to be running for the events to be detected:

        from gpiozero import Button
        from signal import pause

        button = Button(2)
        button.when_pressed = lambda: print("Button was pressed!")
        pause()