.. _arduino_adc:

=======================
1.2 ADC Battery Monitor
=======================

Read the battery voltage with the ESP32-S3's built-in ADC.

Overview
========

This example shows how to read the battery voltage with the ESP32-S3's built-in ADC. On this board, the battery voltage is routed to ``GPIO 19`` through a ``1:4`` voltage divider, so the ADC pin sees one quarter of the actual battery voltage.

What You'll Learn
=================

* Using ``analogRead()`` on the ESP32-S3
* Configuring ADC attenuation with ``analogSetAttenuation()``
* Converting a raw ADC reading into an estimated battery voltage

Before You Begin
================

Complete the setup steps in :ref:`preparation` before continuing.

.. note::
   Use the recommended Arduino IDE settings in :ref:`arduino_board_settings` unless this lesson says otherwise.

Open the example sketch from the code package:

``LAFVIN-ESP32-S3-Multimedia-Kit-main/1.Arduino/2.ADC_Battery/2.ADC_Battery.ino``

This example reads the board's built-in battery measurement circuit. No external wiring is required.

============ ========
Signal       ESP32-S3
============ ========
V_BAT (1/4)  GPIO 19
============ ========

.. tip:: 
   The ADC pin does not receive the full battery voltage directly. The board uses a resistor divider, and the sketch multiplies the measured pin voltage by ``4.0`` to estimate the battery voltage.

Upload and Test
===============

#. Connect the board with a USB Type-C data cable.
#. Open ``2.ADC_Battery.ino`` in Arduino IDE.
#. In the **Tools** menu, select ``ESP32S3 Dev Module`` as the board and choose the correct serial port.
#. Click **Upload**.
#. Open **Serial Monitor**, set the baud rate to ``115200``, and watch the raw ADC value, the divided voltage, and the estimated battery voltage update every 200 ms.

Open the Serial Monitor at ``115200`` baud. You should see readings similar to::

   ADC Val: 2450,   Voltage: 1.97V,   Battery: 7.88V
   ADC Val: 2448,   Voltage: 1.97V,   Battery: 7.88V

.. note::
   The actual reading depends on your power source and battery charge level. A fully charged 2-cell Li-ion battery is typically close to ``8.4V``.

How the Code Works
==================

.. code-block:: cpp

   analogSetAttenuation(ADC_11db);  // Full range: about 0-3.3V

   int raw = analogRead(19);
   float voltage_at_pin = (raw / 4095.0) * 3.3;    // ESP32-S3 ADC is 12-bit
   float battery_voltage = voltage_at_pin * 4.0;   // Compensate for the divider

In the provided sketch:

* ``analogSetAttenuation(ADC_11db)`` expands the measurable input range
* ``analogRead(19)`` gets a 12-bit ADC value from ``0`` to ``4095``
* The raw value is converted to the voltage seen at ``GPIO 19``
* The result is multiplied by ``4.0`` to estimate the real battery voltage
* The sketch prints the readings to the Serial Monitor every 200 ms