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3.1.5 Battery Indicator
============================


.. note::

   .. image:: ../img/mcp3008_and_adc0834.jpg
      :width: 25%
      :align: left
    

   Depending on your kit version, please identify whether you have **ADC0834** or **MCP3008** and proceed with the matching section.


Introduction
--------------

In this course, we will make a battery indicator device that can
visually display the battery level on the LED Bargraph.

Components
------------

.. image:: img/list_Battery_Indicator.png
    :align: center

Schematic Diagram
-------------------

============ ======== ======== ===
T-Board Name physical wiringPi BCM
GPIO17       Pin 11   0        17
GPIO18       Pin 12   1        18
GPIO27       Pin 13   2        27
GPIO25       Pin 22   6        25
GPIO12       Pin 32   26       12
GPIO16       Pin 36   27       16
GPIO20       Pin 38   28       20
GPIO21       Pin 40   29       21
GPIO5        Pin 29   21       5
GPIO6        Pin 31   22       6
GPIO13       Pin 33   23       13
GPIO19       Pin 35   24       19
GPIO26       Pin 37   25       26
============ ======== ======== ===

.. image:: img/Schematic_three_one5.png
   :align: center

Experimental Procedures
-------------------------

**Step 1:** Build the circuit.

.. image:: img/image248.png
   :width: 800
   :align: center


**Step 2:** Go to the folder of the code.

.. raw:: html

   <run></run>

.. code-block:: 

    cd ~/davinci-kit-for-raspberry-pi/c/3.1.5/

**Step 3:** Compile the code.

.. raw:: html

   <run></run>

.. code-block:: 

    gcc 3.1.5_BatteryIndicator.c -lwiringPi

**Step 4:** Run the executable file.

.. raw:: html

   <run></run>

.. code-block:: 

    sudo ./a.out

After the program runs, give the 3rd pin of ADC0834 and the GND a
lead-out wire separately and then lead them to the two poles of a
battery separately. You can see the corresponding LED on the LED
Bargraph is lit up to display the power level (measuring range: 0-5V).

.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`install_wiringpi_pi5`.


**Code Explanation**

.. code-block:: c

    void LedBarGraph(int value){
        for(int i=0;i<10;i++){
            digitalWrite(pins[i],HIGH);
        }
        for(int i=0;i<value;i++){
            digitalWrite(pins[i],LOW);
        }
    }

This function works for controlling the turning on or off of the 10 LEDs
on the LED Bargraph. We give these 10 LEDs high levels to let they are
off at first, then decide how many LEDs are lit up by changing the
received analog value.

.. code-block:: c

    int main(void)
    {
        uchar analogVal;
        if(wiringPiSetup() == -1){ //when initialize wiring failed,print messageto screen
            printf("setup wiringPi failed !");
            return 1;
        }
        pinMode(ADC_CS,  OUTPUT);
        pinMode(ADC_CLK, OUTPUT);
        for(int i=0;i<10;i++){       //make led pins' mode is output
            pinMode(pins[i], OUTPUT);
            digitalWrite(pins[i],HIGH);
        }
        while(1){
            analogVal = get_ADC_Result(0);
            LedBarGraph(analogVal/25);
            delay(100);
        }
        return 0;
    }

analogVal produces values (**0-255**) with varying voltage values
(**0-5V**), ex., if a 3V is detected on a battery, the corresponding
value **152** is displayed on the voltmeter.

The **10** LEDs on the LED Bargraph are used to display the
**analogVal** readings. 255/10=25, so every **25** the analog value
increases, one more LED turns on, ex., if “analogVal=150 (about 3V),
there are 6 LEDs turning on.”