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.. _per_button:

2.2 Button
=================

In this project, we will learn how to turn on or off the LED by using a button.

* :ref:`cpn_bb`
* :ref:`cpn_led`
* :ref:`cpn_res`
* :ref:`cpn_button`

**Wiring**


|button0|


* One side of the button pin is connected to 3.3v, and the other side pin is connected to GP14, so when the button is pressed, GP14 will be high. 
* However, when the button is not pressed, GP14 is in a suspended state and may be high or low. In order to get a stable low level when the button is not pressed, GP14 needs to be reconnected to GND through a 10K pull-down resistor.


**Code**

.. note::

    * You can refer to the image below to write code by dragging and dropping. 
    * Import ``2.2_button.png`` from the path of ``euler-kit\piper``. For detailed tutorials, please refer to :ref:`import_code_piper`.


|2.2_button|

After connecting Pico, click the **Start** button and the code starts to run. When the button is pressed, the LED will be lit. When the button is released, the LED will go out.


**How it Works?**

When the button is pressed, pin14 is high. So if the read pin14 is high, turn the pin15 on (LED is lit); else, turn off the pin15 (LED is off).

* [if () do () else ()]: This is a judgment block, depending on the condition after the [if] block to determine whether to run the blocks inside the [do] block, or the blocks inside the [else] block.
* [is pin () HIGH]: This is used to read the level of a specific pin, if the level read is the same as the set HIGH/LOW, then execute the blocks inside [do] block, otherwise execute the blocks inside [else].