Using 7 segments displays with Arduino and 74HC595 shift registers


Here’s my first take at using this now “famous” 7 segments displays…

I got an old interesting display, composed of 2 7 segments + 1 of 2 segments… I don’t remember where I got it from, but I’m pretty sure it comes from a 486 PC like those that used to display their frequency in MHz, and had a turbo button to go from 80 to 130MHz or something like this… I remember I had a similar one in 1997 !

So here’s the final result:

7 Segments Display with 74HC595 shift registers

And the arduino code  (do notice th “logical NOT” in “~LED_CHAR_SET[data]”, as this is a Common Anode (positive) display, rather than Common Cathode as most of them are):


#include <LED7Segment.h>

const int latchPin = 4; //Pin connected to ST_CP of 74HC595
const int clockPin = 3; //Pin connected to SH_CP of 74HC595
const int dataPin = 2; //Pin connected to DS of 74HC595

void setup() {
 //set pins to output because they are addressed in the main loop
 pinMode(latchPin, OUTPUT);
 pinMode(clockPin, OUTPUT);
 pinMode(dataPin, OUTPUT);
}

void loop() {
 //count up routine
 for (int j = 0; j < 128; j++) {
 display(j/10, j - (j/10) * 10);
 delay(300);
 }
}

void display(byte seg1, byte seg2){
 send(seg1);
 send(seg2);
}

void send(byte data){
 //ground latchPin and hold low for as long as you are transmitting
 digitalWrite(latchPin, LOW);
 shiftOut(dataPin, clockPin, LSBFIRST, ~LED_CHAR_SET[data]);
 //return the latch pin high to signal chip that it no longer needs to listen for information
 digitalWrite(latchPin, HIGH);
}

And the LED7Segment.h, mostly copied after this guy (thanks !) :

// Character set data for 7-segment display

// The first 16 characters are hex digits 0-F, to simplify the display of numerals.
// Characters 16-23 and 24-31 provide an animated "figure-8" cycle with one and two
// segments lit at a time, respectively.
//
// For obvious reasons, some letters and punctuation are rather hard to decipher.
// Rather than duplicate shapes, alternative versions of some characters are offered
// (e.g. 6 7 9, upper/lowercase letters).

// Bit order: DP A B C D E F G
// Segments A-F run clockwise from the top; G is the middle bar; DP = decimal point.
//
// Pins to connect to common-cathode LED display via a 74HC595:
// DP-15, A-1, B-2, C-3, D-4, E-5, F-6, G-7 (shiftOut using LSBFIRST)
// Or:
// DP-7, A-6, B-5, C-4, D-3, E-2, F-1, G-15 (shiftOut using MSBFIRST)

#include "WProgram.h"

const byte LED_CHAR_SET[128] = {
 // 00-0F: Hex digits
 B01111110, B00110000, B01101101, B01111001,    // 0123
 B00110011, B01011011, B01011111, B01110000,    // 4567
 B01111111, B01111011, B01110111, B00011111,    // 89AB
 B01001110, B00111101, B01001111, B01000111,    // CDEF

 // 10-1F: Figure-8 drawing (8-character cycle)
 B01000000, B00100000, B00000001, B00000100,    // 1-segment
 B00001000, B00010000, B00000001, B00000010,

 B01100000, B00100001, B00000101, B00001100,    // 2-segment
 B00011000, B00010001, B00000011, B01000010,

 // 20-2F: Punctuation (barely recognizable!)
 B00000000, B10100000, B00100010, B00111111,    //  !"#
 B01011010, B01001001, B00000111, B00000010,    // $%&'
 B01001110, B01111000, B01100011, B00110001,    // ()*+
 B00010000, B00000001, B10000000, B00100101,    // ,-./

 // 30-3F: Decimal digits (alternate) and more punctuation
 B01111110, B00110000, B01101101, B01111001,    // 0123
 B00110011, B01011011, B00011111, B01110010,    // 4567
 B01111111, B01110011, B01001000, B01010000,    // 89:;
 B00001101, B00001001, B00011001, B11100000,    // <=>?

 // 40-5F: Capital letters and punctuation
 B01101110, B01110111, B00011111, B01001110,    // @ABC
 B01111100, B01001111, B01000111, B01011110,    // DEFG
 B00110111, B00000110, B00111100, B01010111,    // HIJK
 B00001110, B01110110, B00010101, B01111110,    // LMNO

 B01100111, B01110011, B01000110, B01011011,    // PQRS
 B01110000, B00111110, B00111110, B00101011,    // TUVW
 B01110101, B00111011, B01101101, B01001110,    // XYZ[
 B00010011, B01111000, B01100010, B00001000,    // \]^_

 // 60-7F: Lowercase letters and punctuation
 B01100000, B01111101, B00011111, B00001101,    // `abc
 B00111101, B01101111, B01000111, B01111011,    // defg
 B00010111, B00010000, B00011000, B00101111,    // hijk
 B00001100, B01010101, B01101010, B00011101,    // lmno

 B01100111, B01110011, B00000101, B00010011,    // pqrs
 B00001111, B00011100, B00100011, B01011101,    // tuvw
 B01101100, B00111011, B00100101, B01000011,    // xyz{
 B00110110, B01100001, B01000000, B11111111    // |}~
};
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