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.. _3.1.5_c_mcp3008:

3.1.5 Battery Indicator(MCP3008)
==================================

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

.. warning::

    Do not use battery components that exceed 3.3V to avoid overloading, which may damage the chip or Raspberry Pi.

Required Components
------------------------------

In this project, we need the following components.

.. image:: img/list2_Battery_Indicator.png
    :align: center


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

============ ======== ======== ===
T-Board Name physical wiringPi BCM
SPICE0       Pin 24   10       8
SPIMOSI      Pin 19   12       10
SPIMISO      Pin 21   13       9
SPISCLK      Pin 23   14       11
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_battery_indicator_mcp3008.png
   :align: center

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

**Step 1:** Build the circuit.

.. image:: img/july24_3.1.5_battery_indicator_mcp3008.png

**For C Language Users**
^^^^^^^^^^^^^^^^^^^^^^^^^


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

.. raw:: html

   <run></run>

.. code-block:: 

    cd ~/davinci-kit-for-raspberry-pi/c/3.1.5-2/

**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 MCP3008 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`.

Code
--------

.. code-block:: c

    #include <wiringPi.h>
    #include <wiringPiSPI.h>
    #include <stdio.h>

    #define SPI_CHANNEL 0
    #define SPI_SPEED   1000000  // 1MHz
    #define VREF        3.3      

    int pins[10] = {6, 26, 27, 28, 29, 21, 22, 23, 24, 25};

    int read_ADC(int channel)
    {
        if (channel < 0 || channel > 7) return -1;

        unsigned char buffer[3];
        buffer[0] = 1;  // Start bit
        buffer[1] = (8 + channel) << 4;  // Single-ended mode
        buffer[2] = 0;

        wiringPiSPIDataRW(SPI_CHANNEL, buffer, 3);

        int value = ((buffer[1] & 3) << 8) | buffer[2];
        return value;
    }

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

    int main(void)
    {
        if (wiringPiSetup() == -1) {
            printf("setup wiringPi failed!\n");
            return 1;
        }

        if (wiringPiSPISetup(SPI_CHANNEL, SPI_SPEED) == -1) {
            printf("SPI setup failed!\n");
            return 1;
        }

        for (int i = 0; i < 10; i++) {
            pinMode(pins[i], OUTPUT);
            digitalWrite(pins[i], HIGH);
        }

        while (1) {
            int analogVal = read_ADC(0);  // MCP3008 CH0
            if (analogVal < 0) continue;


            float voltage = analogVal * VREF / 1023.0;
            int level = analogVal * 10 / 1024;  
            if (level > 10) level = 10;  

            LedBarGraph(level);

            printf("ADC Value: %d\tVoltage: %.2f V\tLevel: %d\n", analogVal, voltage, level);

            delay(200);
        }

        return 0;
    }


Code Explanation
----------------------
.. code-block:: c

    int read_ADC(int channel)
    {
        if (channel < 0 || channel > 7) return -1;

        unsigned char buffer[3];
        buffer[0] = 1;  // Start bit
        buffer[1] = (8 + channel) << 4;  // Single-ended mode, CH0~CH7
        buffer[2] = 0;

        wiringPiSPIDataRW(SPI_CHANNEL, buffer, 3);

        int value = ((buffer[1] & 3) << 8) | buffer[2];  // Combine 10-bit result
        return value;
    }

This function reads analog values from the MCP3008 ADC chip using SPI.
The ``channel`` parameter selects one of the 8 analog inputs (CH0–CH7).
The MCP3008 returns a 10-bit digital value between 0 and 1023 representing the analog voltage.

.. code-block:: c

    void LedBarGraph(int value) {
        for (int i = 0; i < 10; i++) {
            if (i < value)
                digitalWrite(pins[i], HIGH);  // Turn on LED (assumes active HIGH wiring)
            else
                digitalWrite(pins[i], LOW);   // Turn off LED
        }
    }

This function controls a 10-LED bar graph display.
Each LED represents 1/10th of the voltage range.
LEDs are turned on in order up to the specified level.

Note: This version assumes LED anodes are connected to GPIOs and cathodes to GND (i.e. active HIGH).

.. code-block:: c

    int main(void)
    {
        if (wiringPiSetup() == -1) {
            printf("setup wiringPi failed!\n");
            return 1;
        }

        if (wiringPiSPISetup(SPI_CHANNEL, SPI_SPEED) == -1) {
            printf("SPI setup failed!\n");
            return 1;
        }

        for (int i = 0; i < 10; i++) {
            pinMode(pins[i], OUTPUT);
            digitalWrite(pins[i], HIGH);  // Initialize all LEDs to ON
        }

        while (1) {
            int analogVal = read_ADC(0);  // Read voltage on CH0
            if (analogVal < 0) continue;

            float voltage = analogVal * VREF / 1023.0;
            int level = analogVal * 10 / 1024;  // Map to 0–10 levels
            if (level > 10) level = 10;

            LedBarGraph(level);  // Display level on LEDs

            printf("ADC Value: %d\tVoltage: %.2f V\tLevel: %d\n", analogVal, voltage, level);

            delay(200);  // Update rate: 5 Hz
        }

        return 0;
    }

Main program logic:

- Initializes wiringPi and SPI communication.
- Sets GPIO pins as outputs for controlling the 10-LED bar.
- Continuously reads analog voltage via MCP3008 (CH0).
- Converts the reading to a voltage using ``VREF = 3.3V``.
- Scales voltage to a 0–10 level bar graph and lights up LEDs.
- Displays the raw ADC value, voltage (in volts), and LED level via serial console.

This acts as a visual battery level indicator or analog voltmeter.



**For Python Language Users**
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


**Step 2:** Set up the SPI interface and install the ``spidev`` library (see :ref:`spi_configuration` for detailed instructions). If you have already completed these steps, you can skip this.

**Step 3:** Go to the folder of the code.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/davinci-kit-for-raspberry-pi/python

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

.. raw:: html

   <run></run>

.. code-block::

    sudo python3 3.1.5-2_BatteryIndicator.py

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).

.. warning::

    If there is an error prompt  ``RuntimeError: Cannot determine SOC peripheral base address``, please refer to :ref:`faq_soc` 

**Code**

.. note::
    You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to  source code path like ``davinci-kit-for-raspberry-pi/python``. After modifying the code, you can run it directly to see the effect.

.. raw:: html

    <run></run>

.. code-block:: python


    #!/usr/bin/env python3

    import RPi.GPIO as GPIO
    import spidev
    import time

    # GPIO pins connected to 10 LEDs, ordered from left to right
    led_pins = [25, 12, 16, 20, 21, 5, 6, 13, 19, 26]  # BCM numbering

    # GPIO setup
    GPIO.setmode(GPIO.BCM)
    for pin in led_pins:
        GPIO.setup(pin, GPIO.OUT)
        GPIO.output(pin, GPIO.LOW)

    # Initialize SPI
    spi = spidev.SpiDev()
    spi.open(0, 0)  # Bus 0, CE0
    spi.max_speed_hz = 1000000  # 1 MHz

    # Read value from MCP3008 channel 
    def read_adc(channel):
        if channel < 0 or channel > 7:
            return -1
        r = spi.xfer2([1, (8 + channel) << 4, 0])
        value = ((r[1] & 0x03) << 8) | r[2]
        return value

    # Light up LED bar graph according to value 
    def led_bar_graph(level):
        for i, pin in enumerate(led_pins):
            if i < level:
                GPIO.output(pin, GPIO.HIGH)
            else:
                GPIO.output(pin, GPIO.LOW)

    # Main loop
    try:
        while True:
            analog_val = read_adc(0)  # Read from MCP3008 channel 0
            level = int(analog_val * 10 / 1023)  
            led_bar_graph(level)
            print(f"ADC: {analog_val}, Level: {level}")
            time.sleep(0.2)

    except KeyboardInterrupt:
        pass

    finally:
        for pin in led_pins:
            GPIO.output(pin, GPIO.LOW)
        GPIO.cleanup()
        spi.close()


Code Explanation
--------------------

This program reads analog voltage from an MCP3008 ADC and displays the result on a 10-LED bar graph using a Raspberry Pi (BCM pin layout).

1. **Import Modules**

   - ``RPi.GPIO`` controls the GPIO pins on Raspberry Pi.
   - ``spidev`` communicates with MCP3008 via SPI.
   - ``time`` provides delay/sleep functionality.

   .. code-block:: python

       #!/usr/bin/env python3

       import RPi.GPIO as GPIO
       import spidev
       import time

2. **GPIO LED Setup**

   A list of 10 GPIO pins is defined for LED control. These pins are configured as output and initialized to LOW (off).

   .. code-block:: python

       # GPIO pins connected to 10 LEDs, ordered from left to right
       led_pins = [25, 12, 16, 20, 21, 5, 6, 13, 19, 26]  # BCM numbering

       GPIO.setmode(GPIO.BCM)
       for pin in led_pins:
           GPIO.setup(pin, GPIO.OUT)
           GPIO.output(pin, GPIO.LOW)

3. **SPI Initialization**

   Initializes SPI bus 0 and chip enable 0 (CE0) to communicate with MCP3008.
   The communication speed is set to 1 MHz.

   .. code-block:: python

       spi = spidev.SpiDev()
       spi.open(0, 0)  # Bus 0, CE0
       spi.max_speed_hz = 1000000  # 1 MHz

4. **ADC Read Function**

   Reads an analog value from a specified MCP3008 channel (0–7). The function sends a 3-byte SPI command and decodes the 10-bit result.

   .. code-block:: python

       def read_adc(channel):
           if channel < 0 or channel > 7:
               return -1
           r = spi.xfer2([1, (8 + channel) << 4, 0])
           value = ((r[1] & 0x03) << 8) | r[2]
           return value

5. **LED Bar Graph Function**

   Lights up LEDs based on the analog level. If the level is 7, the first 7 LEDs will be ON and the rest OFF.

   .. code-block:: python

       def led_bar_graph(level):
           for i, pin in enumerate(led_pins):
               if i < level:
                   GPIO.output(pin, GPIO.HIGH)
               else:
                   GPIO.output(pin, GPIO.LOW)

6. **Main Loop**

   Continuously reads analog input from channel 0, scales the result to a value from 0 to 10, and updates the LED display accordingly. Prints ADC and level values for monitoring.

   .. code-block:: python

       try:
           while True:
               analog_val = read_adc(0)
               level = int(analog_val * 10 / 1023)
               led_bar_graph(level)
               print(f"ADC: {analog_val}, Level: {level}")
               time.sleep(0.2)

7. **Cleanup on Exit**

   When ``Ctrl+C`` is pressed, the program turns off all LEDs, cleans up GPIO state, and closes the SPI interface.

   .. code-block:: python

       except KeyboardInterrupt:
           pass

       finally:
           for pin in led_pins:
               GPIO.output(pin, GPIO.LOW)
           GPIO.cleanup()
           spi.close()