A serial-in parallel-out shift register (74HC164, 74HC595, CD4094…..) can be added to a 7-segment display. The adding of the shift register minimizes the number of pins used by the 7-segment display. This topic shows how to make a 4-digit digital counter with multiplexing and 74HC164 shift register using PIC16F877A and CCS PIC C compiler.
Digital up/down counter using PIC16F877A:
Here is an example shows how to make a digital up and down counter where the number is displayed on a 7 segment display uses multiplexing technique with shift register.
Example circuit schematic is shown below where a common anode 7-segment display and 74HC164N shift register are used.
Other shift registers such as 74HC595 or CD4094 can be used in this project.
Two buttons are used to increment and decrement the displayed number.
The PIC16F877A microcontroller must be supplied with 5V between pins VDD (#11) and VSS (#12).
Hardware Required:
- PIC16F877A microcontroller —> datasheet
- Common anode 4-digit seven-segment display
- 74HC164 shift register —> datasheet
- 4 x 2N3906 PNP transistor —> datasheet
- 2 x Push button
- 5 x 10k ohm resistor
- 4 x 1k ohm resistor
- 7 x 100 ohm resistor
- 8 MHz crystal oscillator
- 2 x 22 pF ceramic capacitor
- 5V Power source
- Bread board and some jumper wires
- PIC microcontroller programmer (PICkit 2, PICkit 3…)
Digital up/down counter using PIC16F877A CCS C code:
The C code below is for CCS C compiler, it was tested with version 5.051.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 | // 4-Digit digital counter using PIC16F877A // Common anode 7-segment display with shift register #include <16F877A.h> #use delay(crystal=8000000) short s; // Used to know buttons position unsigned int j, digit, digit1, digit10, digit100,digit1000; unsigned long i = 0; unsigned int seg(unsigned int num) { switch (num) { case 0 : return 0xC0; case 1 : return 0xF9; case 2 : return 0xA4; case 3 : return 0xB0; case 4 : return 0x99; case 5 : return 0x92; case 6 : return 0x82; case 7 : return 0xF8; case 8 : return 0x80; case 9 : return 0x90; } } void main(){ while(TRUE){ if(input(PIN_D0) && input(PIN_D1)) s = 1; if(s == 1) { if(input(PIN_D0) == 0) { s = 0; i++; if(i > 9999) i = 0; } if(input(PIN_D1) == 0) { s = 0; if(i < 1) i = 1; i--; } } digit = i % 10; digit1 = seg(digit); output_c(0x0F); // Turn off all displays for(j = 0x40; j > 0; j = j >> 1) { if(digit1 & j) output_high(PIN_B0); else output_low(PIN_B0); delay_us(10); output_high(PIN_B1); delay_us(10); output_low(PIN_B1);} output_c(0x07); // Turn on display for ones delay_ms(2); digit = (i / 10) % 10; digit10 = seg(digit); output_c(0x0F); // Turn off all displays for(j = 0x40; j > 0; j = j >> 1) { if(digit10 & j) output_high(PIN_B0); else output_low(PIN_B0); delay_us(10); output_high(PIN_B1); delay_us(10); output_low(PIN_B1);} output_c(0x0B); // Turn on display for tens delay_ms(2); digit = (i / 100) % 10; digit100 = seg(digit); output_c(0x0F); // Turn off all displays for(j = 0x40; j > 0; j = j >> 1) { if(digit100 & j) output_high(PIN_B0); else output_low(PIN_B0); delay_us(10); output_high(PIN_B1); delay_us(10); output_low(PIN_B1);} output_c(0x0D); // Turn on display for hundreds delay_ms(2); digit = (i / 1000) % 10; digit1000 = seg(digit); output_c(0x0F); // Turn off all displays for(j = 0x40; j > 0; j = j >> 1) { if(digit1000 & j) output_high(PIN_B0); else output_low(PIN_B0); delay_us(10); output_high(PIN_B1); delay_us(10); output_low(PIN_B1);} output_c(0x0E); // Turn on display for thousands delay_ms(2); } } |
Digital up/down counter using PIC16F877A video:
The following video from a real hardware circuit for the digital counter.
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