Show Number

In this project, we use processing to drive a 7-segment display to show a figure from 0 to 9 and A to F.

Wiring

• GPIO Extension Board

• Breadboard

• Resistor

• 7-segment Display

• 74HC595

Sketch

import processing.io.*;

int SDI=17;   //serial data input
int RCLK=18;  //memory clock input(STCP)
int SRCLK =27;   //shift register clock input(SHCP)


int[] SegCode= {0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71};

void hc595_shift(int dat){
  int i;

  for(i=0;i<8;i++){
        int n=(0x80 & (dat << i));
        if ( n==0){
          GPIO.digitalWrite(SDI, 0);
        } else {
          GPIO.digitalWrite(SDI, 1);
        }
        GPIO.digitalWrite(SRCLK, 1);
        delay(1);
        GPIO.digitalWrite(SRCLK, 0);
  }

        GPIO.digitalWrite(RCLK, 1);
        delay(1);
        GPIO.digitalWrite(RCLK, 0);
}

void setup() {
        size(400, 200);
        frameRate(10);

        GPIO.pinMode(SDI, GPIO.OUTPUT);
        GPIO.pinMode(RCLK, GPIO.OUTPUT);
        GPIO.pinMode(SRCLK, GPIO.OUTPUT);

        GPIO.digitalWrite(SDI, 0);
        GPIO.digitalWrite(RCLK, 0);
        GPIO.digitalWrite(SRCLK, 0);

        fill(0,25,88);
        textAlign(CENTER,CENTER);
        textSize(height*0.8);
}

void draw() {

        background(255);
        int number = (frameCount%100)/10;
        text(number, width/2, height/2);
        hc595_shift(SegCode[number]);
}

How it works?

Import processing.io.* and use the GPIO function library to control the digital tube pins.

Define array SegCode = {0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71} which represents a segment code array from 0 to F in Hexadecimal (Common cathode).

setup() function sets the three pins SDI,RCLK and SRCLK as output, and the initial data as 0.

hc595_shift(int dat) function is used to shift the SegCode to 74HC595.

void hc595_shift(int dat){
  int i;

  for(i=0;i<8;i++){
        int n=(0x80 & (dat << i));
        if ( n==0){
          GPIO.digitalWrite(SDI, 0);
        } else {
          GPIO.digitalWrite(SDI, 1);
        }
        GPIO.digitalWrite(SRCLK, 1);
        delay(1);
        GPIO.digitalWrite(SRCLK, 0);
  }

        GPIO.digitalWrite(RCLK, 1);
        delay(1);
        GPIO.digitalWrite(RCLK, 0);
}

n=(0x80 & (dat << i)) means to shift dat to the left by i bits and then do the & operation with 0x80.

The rule of & operation is that when both sides of & are 1, the result is 1, otherwise the result is 0.

For example, we assume dat=0x3f,i=2(0011 1111 << 2 shift to 1111 1100), then 1111 1100 & 1000 0000 (0x80)) = 1000 0000.

At last assign the dat data to SDI(DS) by bits.

digitalWrite(SRCLK, 1) when SRCLK generates a rising edge pulse from 0 to 1, the data will be transferred from the DS register to the shift register;

digitalWrite(RCLK, 1) when RCLK generates a rising edge pulse from 0 to 1, the data will be transferred from the shift register to the storage register.

fill(0,25,88);
textAlign(CENTER,CENTER);
textSize(height*0.8);

The fill() function used in setup() can fill the text color, textAlign(CENTER,CENTER) is used to center the text, textSize(height*0.8) change the text height to 0.8 times the original. These functions can customize the text style displayed on the processing

void draw() {

        background(255);
        int number = (frameCount%100)/10;
        text(number, width/2, height/2);
        hc595_shift(SegCode[number]);
}

The frameCount is a seed, which is related to frameRate. By default frameRate is 60, which means that frameCount will accumulate 60 times per second.

Then we can let processing and 7-segment display to show the figure from 0 to 9 and A to F simultaneously.