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.. _per_water_tank:

2.6 Smart Water Tank
=============================

In this project, we use a water level sensor module and a servo to simulate a smart water tank. The water level sensor is fixed inside the tank to measure the water level, and when the water level is below a threshold, the valve controlled by the servo is allowed to open to let water in.

* :ref:`cpn_bb`
* :ref:`cpn_water`
* :ref:`cpn_servo`



**Wiring**

|pin_adc|

Pico has three GPIO pins that can use analog input, GP26, GP27, GP28. That is, analog channels 0, 1, and 2.
In addition, there is a fourth analog channel, which is connected to the built-in temperature sensor and will not be introduced here.


|water_tank0|

* S of water level sensor is connected to GP26(A0), + to VBUS, - pin to GND.
* The orange wire (signal) of the servo is connected to GP15, the red wire (power) is connected to VBUS, and the brown wire (ground) is connected to GND. 

**Code**

.. note::

    * You can refer to the image below to write code by dragging and dropping. 
    * Import ``2.6_water_tank.png`` from the path of ``euler-kit\piper``. For detailed tutorials, please refer to :ref:`import_code_piper`.

|water_tank|



After connecting Pico, click the **Start** button and the code starts to run. When the water level is lower than 1/3 of the water level sensor, the servo rotates to 180 degrees to simulate the inlet opening; when the water level is higher than 1/3 of the water level sensor, the servo rotates to 0 degrees to imitate the inlet closing.

**How it Works?**

|water_tank1|

Set the rotation speed of pin15 (servo) to 15%.

* [servo pin() set speed to ()%]：Used to set the rotation speed of the servo pin, the range is 0%~100%.

|water_tank2|

Reads the value of pin A0 and stores it in the variable [water_level].

* [set (water_level) to]: Used to set the value of the variable, you need to create the variable from the **Variables** palette.
* [read voltage from pin ()]: Used to read the voltage of the analog pins (A0~A2), the range is 0 ~ 3.3V.

|water_tank3|

Set the voltage threshold to 1. When the voltage of water level sensor is less than 1, let the servo rotate to 180° position, otherwise rotate to 0° position.

* [servo pin () set angle to ()]: Set the angle of servo pin to, the range is 0 ~ 180°.