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.. _1.1.5_4digit_nodejs:

1.1.5 4-Digit 7-Segment Display
====================================

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

Next, follow me to try to control the 4-digit 7-segment display.

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

.. image:: img/list_4_digit.png



.. note::
    In this projiect, for the 4-Digit 7-Segment Display we should use BS model,if you use AS model it may not light up.

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

.. image:: img/schmatic_4_digit.png


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

**Step 1**: Build the circuit.

.. image:: img/image80.png

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

.. raw:: html

    <run></run>

.. code-block::

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

**Step 3**: Run the code.

.. raw:: html

    <run></run>

.. code-block::

    sudo node 4_digit_7_segment_display.js

After the code runs, the program takes a count, increasing by 1 per second, and the 4-digit 7-segment display displays the count.
 
**Code**

.. code-block:: js

    const Gpio = require('pigpio').Gpio;

    var counter = 0;

    const number = [0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90]; //for BS
    
    const SDI = new Gpio(24, { mode: Gpio.OUTPUT });
    const RCLK = new Gpio(23, { mode: Gpio.OUTPUT });
    const SRCLK = new Gpio(18, { mode: Gpio.OUTPUT });

    const pin1 = new Gpio(10, { mode: Gpio.OUTPUT });
    const pin2 = new Gpio(22, { mode: Gpio.OUTPUT });
    const pin3 = new Gpio(27, { mode: Gpio.OUTPUT });
    const pin4 = new Gpio(17, { mode: Gpio.OUTPUT });
    const placePin = [pin1, pin2, pin3, pin4];

    function clearDisplay() {
        hc595_shift(0xff); //for BS
    }

    function hc595_shift(dat) {
        for (let j = 0; j < 8; j++) {
            let code = 0x80 & (dat << j);
            if (code != 0) {
                code = 1;
            }
            SDI.digitalWrite(code);
            SRCLK.trigger(1,1);
        }
        RCLK.trigger(1,1);
    }

    function pickDigit(digit) {
        for(let i=0;i<4;i++){
            placePin[i].digitalWrite(0);
        }
        placePin[digit].digitalWrite(1);
    }


    let digit = -1
    setInterval(() => {
        digit = (digit +1)% 4
        clearDisplay();
        pickDigit(digit);
        switch(digit){
            case 0:
                hc595_shift(number[Math.floor(counter % 10)]);  
                break;
            case 1:
                hc595_shift(number[Math.floor(counter % 100 / 10)]);
                break;        
            case 2:
                hc595_shift(number[Math.floor(counter % 1000 / 100)]);
                break;        
            case 3:
                hc595_shift(number[Math.floor(counter % 10000 / 1000)]);
                break;
        }
    }, 5);

    setInterval(() => {
        counter++;
    }, 1000);

**Code Explanation**

.. code-block:: js

    const pin1 = new Gpio(10, {mode: Gpio.OUTPUT});
    const pin2 = new Gpio(25, {mode: Gpio.OUTPUT});
    const pin3 = new Gpio(27, {mode: Gpio.OUTPUT});
    const pin4 = new Gpio(17, {mode: Gpio.OUTPUT});
    const placePin = [pin1,pin2,pin3,pin4];    

Initialize pins 10, 25, 27, and 17 as output modes and place them in the array ``placePin`` to facilitate control of the common anode of the four-digit 7-segment display.

.. code-block:: js

    const number = [0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90];

Define a constant array ``number`` to represent the hexadecimal segment code from 0 to 9 (common anode).

.. code-block:: js

    function clearDisplay() {
        hc595_shift(0xff); 
    }

Write 0xff to turn off the digital tube.

.. code-block:: js

    function pickDigit(digit) {
        for(let i=0;i<4;i++){
            placePin[i].digitalWrite(0);
        }
        placePin[digit].digitalWrite(1);
    }

Select the place of the value. 
there is only one place that should be enable each time. 
The enabled place will be written high.

.. code-block:: js

    let digit = -1
    setInterval(() => {
        digit = (digit +1)% 4
        clearDisplay();
        pickDigit(digit);
        switch(digit){
            case 0:
                hc595_shift(number[Math.floor(counter % 10)]);  
                break;
            case 1:
                hc595_shift(number[Math.floor(counter % 100 / 10)]);
                break;        
            case 2:
                hc595_shift(number[Math.floor(counter % 1000 / 100)]);
                break;        
            case 3:
                hc595_shift(number[Math.floor(counter % 10000 / 1000)]);
                break;
        }
    }, 5);

this code is used to set the number displayed on the 4-digit 7-segment Dispaly.

First, start the fourth segment display, write the single-digit number. 
Then start the third segment display, and type in the tens digit; 
after that, start the second and the first segment display respectively, 
and write the hundreds and thousands digits respectively. 
Because the refreshing speed is very fast, we see a complete four-digit display.

.. code-block:: js

    setInterval(() => {
        counter++;
    }, 1000);

Add one to the ``counter`` 
(the four-digit digital tube displays the number plus one) 
every second that passes.

Phenomenon Picture
-------------------------

.. image:: img/image81.jpeg