[Solved] 74HC595N all outputs high no matter what I do

Other Hardware LEDs and Multiplexing
1

Hi, I’m dealing with the 74HC595N shift register to control 8 LEDs.
The connections are done exactly as it’s shown in the image

imagen
imagen1920×2198 654 KB

The code is really simple, and it’s read as follows:


int SER =8;
int LATCH =9;
int CLK =10;

void setup()
{
   pinMode(SER, OUTPUT);
   pinMode(LATCH, OUTPUT); 
   pinMode(CLK, OUTPUT);
   digitalWrite(LATCH, LOW);
   shiftOut(SER, CLK, MSBFIRST, B10101010);
   digitalWrite(LATCH, HIGH);
}
void loop(){}

The problem is that no matter what Number I send to the shift register, either integer or binary, the 8 LEDs glow constantly when arduino is connected. Even if there’s no code, just plugging-in the arduino is sufficient to glow every single LED. This seems quite weird to me, I’ve already checked all my connections, and it looks everything is fine.

2

Let’s see your actual wiring.

Change the series resistors to a higher value, try about 1k

Add de-coupling to to the Vcc pin 16.

3

Thank you so much for your answer, I’m not sure I understand “de-coupling to the VCC”, I’m afraid I’m not so good in electronics.

4

Place a 100nF capacitor close to pin 16 (between GND and 16 which is 5V).

image

The load is the chip, pins 16 and 8

5

Oh I see, thank you, I’ll try it tomorrow after buying one because unfortunately I don’t have any capacitor.
Anyway, in what sense the 1k resistor changes could be a good idea? I thought a 220Ω resistor was quite enough to current-limit the 2-3 V LEDs.
Actually, I have a 470 μF capacitor, would it work?

6

Make sure to buy a ceramic 0.1uF capacitor. Any other type of capacitor will not work.
See:- http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

1 Like
7

I you are serious in learning this stuff and you want to properly communicate with people about your project, you need to learn to post a proper schematic of the circuit you are referring to.

2022-11-06_11-17-27
2022-11-06_11-17-271444×940 195 KB

Also, make your test sketches a bit more dynamic.

Example:

int SER              = 8;
int LATCH            = 9;
int CLK              = 10;

unsigned int counter = 0;


//*********************************************************************************
void setup()
{
  pinMode(SER, OUTPUT);
  pinMode(CLK, OUTPUT);
  pinMode(LATCH, OUTPUT);

  //digitalWrite(LATCH, LOW);
  //shiftOut(SER, CLK, LSBFIRST, B10101010);
  //digitalWrite(LATCH, HIGH);

} //END of   setup()


//*********************************************************************************
void loop()
{
  digitalWrite(LATCH, LOW);
  shiftOut(SER, CLK, LSBFIRST, counter++);
  digitalWrite(LATCH, HIGH);
  delay(200);

} //END of   loop()
1 Like
8

Hi,
this is your code.
I made a small change to it just to give it "movement".

It works correctly.
I see some possibilities:
Or, as already mentioned, the lack of capacitors is proving failures;
or you connected something wrong in your assembly;
or your 74HC595 is faulty.

1 Like
9

Please post clear, complete images of your actual wiring.

10

Thank you so much guys.
LarryD thank you, I supposed it wasn’t the best option but I though it was better than posting a photo of my actual wiring. What software would you recommend me for making my own schematics?
Also, I know there are several programs that help you simulating the behaviour of your circuits, do you know some I could start with?

11

EasyEDA or KiCAD are good options for drawing schematics, a pencil and paper works too.

1 Like
12

I started drawing schematics with pencil and paper (and a big eraser)!

13

See reply #8

1 Like
14

Updating:
I replaced 220Ω resistors by 1K, also added the 0.1μF de-coupling capacitor (ceramic) as you told me.
It’s acting the same way. Just a lower bright of the LEDs.

15

See post #9. Something is wrong with your setup.

16

The schematic and sketch in post #7 works perfectly here.

You must have a bad component or miswiring.

Note:
You might have bad wires too. :thinking:

17

Finally. The chip was the problem, I just bought another and replaced it. It works perfect. Thank you!!!!🫶🏿

18

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19

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