Help controlling a 595 shift register

Using Arduino LEDs and Multiplexing
1

Hi, i am trying to control a pair of 74hc595n's. I did this successfully using python and the RPi, and having set the hardware up the same way i cannot work out how to output how i desire.

int dataPin = 2;
int latchPin = 3;
int clockPin = 4;
int data_out[] = {0,1,0,1, 0,1,0,1, 0,1,0,1, 0,1,0,1};

void setup() {
  // put your setup code here, to run once:

pinMode(dataPin, OUTPUT);
pinMode(latchPin, OUTPUT);
pinMode(clockPin, OUTPUT);

}

void loop() {
  
  // put your main code here, to run repeatedly: 
  digitalWrite(latchPin, LOW);
  for (int thisLed = 0; thisLed < 16; thisLed++) 
  
    if (data_out[thisLed] != 0)
      digitalWrite(dataPin, HIGH);
    else 
      digitalWrite(dataPin, LOW);
    
    digitalWrite(clockPin, HIGH);
    digitalWrite(clockPin, LOW);
  digitalWrite(latchPin, HIGH);
  delay(500);
}

when this is uploaded to my nano all the outputs are high! can anyone see what i have done wrong?

2

Hi, I think you would be better off using the shiftOut() function. Also, pack your data bits into bytes with "B00010011" instead of "{0,0,0,1,0,0,1,1}".

I think the reason your code doesn't work is that there are some missing {}, so the compiler doesn't know which commands are inside the for loop. In Python, the line indentation tells the compiler what's in the loop, but C needs those brackets!

Paul

3

thanks for the reply

i knew there was a shift function, but i wanted to try and do it by hand to get used to arduino and C

i'll search out those curly brackets now :slight_smile:

EDIT:
curly brackets fixed it. thank you

4

zomzilla:
Hi, i am trying to control a pair of 74hc595n's. I did this successfully using python and the RPi, and having set the hardware up the same way i cannot work out how to output how i desire.

int dataPin = 2;

int latchPin = 3;
int clockPin = 4;
int data_out[] = {0,1,0,1, 0,1,0,1, 0,1,0,1, 0,1,0,1};

void setup() {
  // put your setup code here, to run once:

pinMode(dataPin, OUTPUT);
pinMode(latchPin, OUTPUT);
pinMode(clockPin, OUTPUT);

}

void loop() {
 
  // put your main code here, to run repeatedly:
  digitalWrite(latchPin, LOW);
  for (int thisLed = 0; thisLed < 16; thisLed++)
 
    if (data_out[thisLed] != 0)
      digitalWrite(dataPin, HIGH);
    else
      digitalWrite(dataPin, LOW);
   
    digitalWrite(clockPin, HIGH);
    digitalWrite(clockPin, LOW);
  digitalWrite(latchPin, HIGH);
  delay(500);
}




when this is uploaded to my nano all the outputs are high! can anyone see what i have done wrong?

This isn't Python, you need to put in some { and } to show which statements are inside the loop.

5

By the looks of it all you're doing is setting the data pin to high and then sending your data..

But the clock is not toggled back to low/high until your loop finishes

6

Yes, use shiftOut. It's easiest for most shift register needs. IF you want to really do it manually.... go find the shiftOut function in the "wiring_shift.c" library (somewhere in your Arduino folder) and dissect the code it uses.

7

Use SPI, way faster:

digitalWrite(ssPin, LOW);
SPI.transfer(your_data_byte);
digitalWrite (ssPin, HIGH);

and then replace the digitalWrite's with direct port manipulation, such as:

PORTB = PORTB & B11111011; // clear PB2 (SS pin, D10)
SPI.transfer(your_data_byte);
PORTB = PORTB | B00000100; // set PB2 (SS pin, D10)

Got fast hardware for shifting out data, learn to use it.