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1.1.5 4-Digit 7-Segment Display¶

Introduction¶

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

Required Components¶

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
4-Digit 7-Segment Display	-
74HC595	BUY

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¶

Experimental Procedures¶

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/nodejs/

Step 3: Run the code.

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

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

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.

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).

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

Write 0xff to turn off the digital tube.

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.

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.

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

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

1.1.5 4-Digit 7-Segment Display¶

Introduction¶

Required Components¶

Schematic Diagram¶

Experimental Procedures¶

Phenomenon Picture¶