4 digit 7 segment display with 74HC595 IC on Elegoo Arduino UNO R3 project #20

[dcerner]

Hello All, any insight/ shared experience on this is welcome. This is from an Elegoo Super Starter Kit. There isn't any readout after entering code. All components independently verified, and work on other projects. It appears from manual that it might readout: 'HALO' or 'FFFF'. If I flip 5 V and GND on R3 board I get all segments light up??Use code tags to format code for the forum

Code used:

 int latch=9;  //74HC595  pin 9 STCP
int clock=10; //74HC595  pin 10 SHCP
int data=8;   //74HC595  pin 8 DS

unsigned char table[]=
{0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c
,0x39,0x5e,0x79,0x71,0x00};

void setup() {
  pinMode(latch,OUTPUT);
  pinMode(clock,OUTPUT);
  pinMode(data,OUTPUT);
}
void Display(unsigned char num)
{

  digitalWrite(latch,LOW);
  shiftOut(data,clock,MSBFIRST,table[num]);
  digitalWrite(latch,HIGH);
  
}
void loop() {
  Display(1);
  delay(500);
  Display(2);
  delay(500);
  Display(3);
  delay(500);
  Display(4);
  delay(500);
  Display(5);
  delay(500);
  Display(6);
  delay(500);
  Display(7);
  delay(500);
  Display(8);
  delay(500);
  Display(9);
  delay(500);
  Display(10);
  delay(500);
  Display(11);
  delay(500);
  Display(12);
  delay(500);
  Display(13);
  delay(500);
  Display(14);
  delay(500);
  Display(15);
  delay(500);
}

[ruilviana]

Post your project schematic.
How HC595 is wired to 7 segment?
Your 7 segment is common cathode or common anode.

[Railroader]

@dcerner

If I flip 5 V and GND

Randomly connecting circuits is the way to burn things down.

[alto777]

Welcome to the forum.

@dcerner

It appears from manual that it might readout: 'HALO' or 'FFFF'

It appears from the code that it shoukd diplay four identical characters at a time and cycle 0, 1, 2 and so forth alla way to F, the hex digits.

This code looks like you've copied and pasted it or typed it accurately. There are lotsa wires, so at this point we can't really help,you find the ones that are wrong or missing.

Welcome to the hobby.

And

@dcerner

If I flip 5 V and GND on R3 board

Yeah, don't get creative like that. At this point you should be duplicating precisely every line of code and every wire. Uninformed experiments may damage things… it's hard enough when you are sure you have good parts.

Have you had any trouble with projects 1 to 19? What kind of mistakes did you make typically? Did earlier projects use the '595 IC?

a7

[dcerner]

Good question..I want to say common cathode.

[dcerner]

Thanks for question.. No problems like this one in previous 19 projects. Yes, the 1 digit 7 segment used the 595 IC. Typically, simple errors like Port #, etc.

[TwirlyWhirly555]

You have

int latch=9; //74HC595 pin 9 STCP
int clock=10; //74HC595 pin 10 SHCP
int data=8; //74HC595 pin 8 DS

Pin 10 on the 595 is the reset pin and needs to be held high to allow the 595 to operate, The Clock pin should be connected to pin 11 of the 595.

Pin 13 is OE and need to be low for the outputs to work

Pin 14 on the 595 is Data in and Pin 12 is Latch

Like this ;

int latch=9; //74HC595 pin 12 STCP
int clock=10; //74HC595 pin 11 SHCP
int data=8; //74HC595 pin 14 DS

The diagram looks to have these setup correctly but wanted to mention it, You are missing 5V on pin 10 to enable the 595 so this may also factor in to why its not working, So I would check this first and see.

With all 4 cathodes tied to ground you will get all four 7 segment displays showing the same thing ; as I understand that's your current intended goal so that should be fine.

Also to note, the 4 digit 7 segment is multiplexed ; You cannot just connect all 4 cathodes ( assuming common cathode ) to ground if you want to display different things on each 7 segment as the ABC ect segments are common to each other so trying to display something on one 7 segment will show on the other three displays.

With the multiplexed 7 segments you need to switch each cathode to ground one after the other displaying the numbers one after the other ; do this very fast and they all look to be on.

[alto777]

@TwirlyWhirly555 nice catching on wiring errors and/or omissions.

@TwirlyWhirly555

Also to note, the 4 digit 7 segment is multiplexed

True. Presumably to be done in Project 21 or later.

a7

[dcerner]

Twirly, Thank you for sharing your technical support.. very good insight. One jumper BTW 10 & 16 restores correct function. Next, I'll ponder your thoughts on multiplexing.

[TwirlyWhirly555]

No problem, Glad you found the issue.