7-Segment Display With 74HC595 Shift Register | Arduino Projects

Adding a serial-in parallel-out shift register such as the popular one 74HC595 to a 7-segment display will reduce number of pins required to drive it display. Basically the 7-segment display requires 9 pins: 8 segment pins (A, B, C, D, E, F, G and DP) + common pin. By connecting all the segment pins to a shift register, the required number of pins becomes just 3: clock pin and data pin (for the shift register) + common pin. So for a 4-digit 7-segment display we need just 6 pins: clock, data and 4 common pins (each digit has its individual common pin).

This post shows how to build a simple digital counter using Arduino, common anode 7-segment display with 4 digits, and 74HC595 shift register.

To see how to interface the Arduino with 7-segment display without shift register visit the following post: Interfacing Arduino with 7-segment display | 4-Digit counter example

Hardware Required:

• Arduino UNO board   —> ATMEGA328P datasheet
• 4-Digit common anode 7-segment display
• 74HC595 shift register   —->   datasheet
• 4 x PNP transistor (2SA1015, 2S9015, 2N3906 …)
• 8 x 100 ohm resistor
• 4 x 4.7k ohm resistor
• Push button
• Breadboard
• Jumper wires

Arduino 7-Segment display with 74HC595 shift register circuit: The image below shows our example circuit schematic diagram. Most wire connection is between the 4-digit 7-segment display module and the serial-in parallel-out shift register 74HC595.

As shown in the circuit diagram above, all segment pins are connected to the 74HC595 output pins, each one through 100 ohm resistor, where: Segment A … G are connected to 74HC595 pin Q7 … Q1 respectively and segment DP is connected to pin Q0. The data pin of the 74HC595 shift register is named DS (#14) and it is connected to Arduino pin 6. ST_CP (or RCLK) and SH_CP (or SRCLK) are connected together which then connected to Arduino pin 7. This is the clock pin.

Since the display has 4 digits there’re 4 common pins: 1 (most left), 2, 3 and 4. Each common pin is connected to collector terminal of one transistor. Emitter terminals of the 4 transistors are connected to +5V which comes from the Arduino board. Base terminals of the four transistors are connected to Arduino through 4.7k resistors.

The 4 transistors are of the same type (PNP).

The push button which is connected to Arduino analog pin 0 (A0) is used to increment the displayed number.

7-Segment display with 74HC595 shift register code: The Arduino code below doesn’t use any library for the 7-segment display.

The button connection is defined in the code as:

// counter button definition #define button A0

12	// counter button definition#define button A0

Shift register clock pin and data pin are defined as:

// shift register pin definitions #define clockPin 7 // clock pin #define dataPin 6 // data pin

123	// shift register pin definitions#define clockPin 7 // clock pin#define dataPin 6 // data pin

The display needs to be refreshed periodically, for that I used Timer1 module interrupt with the following configuration:

// Timer1 module overflow interrupt configuration TCCR1A = 0; TCCR1B = 1; // enable Timer1 with prescaler = 1 ( 16 ticks each 1 µs) TCNT1 = 0; // set Timer1 preload value to 0 (reset) TIMSK1 = 1; // enable Timer1 overflow interrupt

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// Timer1 module overflow interrupt configurationTCCR1A=0;TCCR1B=1;// enable Timer1 with prescaler = 1 ( 16 ticks each 1 µs)TCNT1=0;// set Timer1 preload value to 0 (reset)TIMSK1=1;// enable Timer1 overflow interrupt

With Timer1 prescaler = 1, we’ve an interrupt every 4096 microseconds. That means every digit is displayed for 4096 us. { 4096 us = 65536 / (16 * prescaler) } Note that Timer1 module is 16-bit timer and Arduino clock frequency is 16MHz.

Functions used in the code: ISR(TIMER1_OVF_vect) : is Timer1 interrupt function, when the microcontroller interrupted by Timer1 it will directly execute this ‘function’.

void disp(byte number, bool dec_point = 0) : this function is for printing data on the 7-segment display, it prints the variable number which may vary between 0 and 9. The variable dec_point decides whether the DP will be printed or not, the default value is 0 (don’t print), if dec_point = 1 the DP segment will be ON.

void disp_off() : this function turns off the whole display.

I used Arduino shiftOut function (built-in) to send data serially to the 74HC595 shift register.

Full Arduino code:

/* * 7-segment display with 74HC595 shift register * 4-Digit counter example. * Common anode 7-segment display is used. * This is a free software with NO WARRANTY. * https://simple-circuit.com/ */ // counter button definition #define button A0 // shift register pin definitions #define clockPin 7 // clock pin #define dataPin 6 // data pin // common pins of the four digits definitions #define Dig1 5 #define Dig2 4 #define Dig3 3 #define Dig4 2 // variable declarations byte current_digit; int count = 0; void disp(byte number, bool dec_point = 0); void setup() { pinMode(button, INPUT_PULLUP); pinMode(Dig1, OUTPUT); pinMode(Dig2, OUTPUT); pinMode(Dig3, OUTPUT); pinMode(Dig4, OUTPUT); pinMode(clockPin, OUTPUT); pinMode(dataPin, OUTPUT); disp_off(); // turn off the display // Timer1 module overflow interrupt configuration TCCR1A = 0; TCCR1B = 1; // enable Timer1 with prescaler = 1 ( 16 ticks each 1 µs) TCNT1 = 0; // set Timer1 preload value to 0 (reset) TIMSK1 = 1; // enable Timer1 overflow interrupt } ISR(TIMER1_OVF_vect) // Timer1 interrupt service routine (ISR) { disp_off(); // turn off the display switch (current_digit) { case 1: disp(count / 1000); // prepare to display digit 1 (most left) digitalWrite(Dig1, LOW); // turn on digit 1 break; case 2: disp( (count / 100) % 10 ); // prepare to display digit 2 digitalWrite(Dig2, LOW); // turn on digit 2 break; case 3: disp( (count / 10) % 10 ); // prepare to display digit 3 digitalWrite(Dig3, LOW); // turn on digit 3 break; case 4: disp(count % 10); // prepare to display digit 4 (most right) digitalWrite(Dig4, LOW); // turn on digit 4 } current_digit = (current_digit % 4) + 1; } // main loop void loop() { if(digitalRead(button) == 0) { count++; // increment 'count' by 1 if(count > 9999) count = 0; delay(200); // wait 200 milliseconds } } void disp(byte number, bool dec_point) { switch (number) { case 0: // print 0 shiftOut(dataPin, clockPin, MSBFIRST, 0x02 | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 1: // print 1 shiftOut(dataPin, clockPin, MSBFIRST, 0x9E | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 2: // print 2 shiftOut(dataPin, clockPin, MSBFIRST, 0x24 | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 3: // print 3 shiftOut(dataPin, clockPin, MSBFIRST, 0x0C | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 4: // print 4 shiftOut(dataPin, clockPin, MSBFIRST, 0x98 | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 5: // print 5 shiftOut(dataPin, clockPin, MSBFIRST, 0x48 | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 6: // print 6 shiftOut(dataPin, clockPin, MSBFIRST, 0x40 | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 7: // print 7 shiftOut(dataPin, clockPin, MSBFIRST, 0x1E | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 8: // print 8 shiftOut(dataPin, clockPin, MSBFIRST, !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); break; case 9: // print 9 shiftOut(dataPin, clockPin, MSBFIRST, 0x08 | !dec_point); digitalWrite(clockPin, HIGH); digitalWrite(clockPin, LOW); } } void disp_off() { digitalWrite(Dig1, HIGH); digitalWrite(Dig2, HIGH); digitalWrite(Dig3, HIGH); digitalWrite(Dig4, HIGH); } // end of code.

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/* * 7-segment display with 74HC595 shift register * 4-Digit counter example. * Common anode 7-segment display is used. * This is a free software with NO WARRANTY. * https://simple-circuit.com/ */ // counter button definition#define button A0 // shift register pin definitions#define clockPin 7 // clock pin#define dataPin 6 // data pin // common pins of the four digits definitions#define Dig1 5#define Dig2 4#define Dig3 3#define Dig4 2 // variable declarationsbytecurrent_digit;intcount=0;voiddisp(bytenumber,booldec_point=0); voidsetup(){pinMode(button,INPUT_PULLUP);pinMode(Dig1,OUTPUT);pinMode(Dig2,OUTPUT);pinMode(Dig3,OUTPUT);pinMode(Dig4,OUTPUT);pinMode(clockPin,OUTPUT);pinMode(dataPin,OUTPUT); disp_off();// turn off the display // Timer1 module overflow interrupt configurationTCCR1A=0;TCCR1B=1;// enable Timer1 with prescaler = 1 ( 16 ticks each 1 µs)TCNT1=0;// set Timer1 preload value to 0 (reset)TIMSK1=1;// enable Timer1 overflow interrupt} ISR(TIMER1_OVF_vect)// Timer1 interrupt service routine (ISR){disp_off();// turn off the display switch(current_digit){case1:disp(count/1000);// prepare to display digit 1 (most left)digitalWrite(Dig1,LOW);// turn on digit 1break; case2:disp((count/100)%10);// prepare to display digit 2digitalWrite(Dig2,LOW);// turn on digit 2break; case3:disp((count/10)%10);// prepare to display digit 3digitalWrite(Dig3,LOW);// turn on digit 3break; case4:disp(count%10);// prepare to display digit 4 (most right)digitalWrite(Dig4,LOW);// turn on digit 4} current_digit=(current_digit%4)+1;} // main loopvoidloop(){if(digitalRead(button)==0){count++;// increment 'count' by 1if(count>9999)count=0;delay(200);// wait 200 milliseconds}} voiddisp(bytenumber,booldec_point){switch(number){case0:// print 0shiftOut(dataPin,clockPin,MSBFIRST,0x02|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case1:// print 1shiftOut(dataPin,clockPin,MSBFIRST,0x9E|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case2:// print 2shiftOut(dataPin,clockPin,MSBFIRST,0x24|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case3:// print 3shiftOut(dataPin,clockPin,MSBFIRST,0x0C|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case4:// print 4shiftOut(dataPin,clockPin,MSBFIRST,0x98|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case5:// print 5shiftOut(dataPin,clockPin,MSBFIRST,0x48|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case6:// print 6shiftOut(dataPin,clockPin,MSBFIRST,0x40|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break;case7:// print 7shiftOut(dataPin,clockPin,MSBFIRST,0x1E|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case8:// print 8shiftOut(dataPin,clockPin,MSBFIRST,!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);break; case9:// print 9shiftOut(dataPin,clockPin,MSBFIRST,0x08|!dec_point);digitalWrite(clockPin,HIGH);digitalWrite(clockPin,LOW);}} voiddisp_off(){digitalWrite(Dig1,HIGH);digitalWrite(Dig2,HIGH);digitalWrite(Dig3,HIGH);digitalWrite(Dig4,HIGH);} // end of code.

The result of this example should be the same as the one shown in the following video (4-digit counter without shift register):

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