Using forLoop and byte arrays for cycling through 595 shift register outputs

Using Arduino Programming Questions
#1

Hello all,
I’m trying to turn on and off an LED, then go to the next LED in line and do the same, with a for loop going through all outputs. (Using solenoids for finished product but using LEDs here for simplicity) I am currently using 2 595 shift registers to control 16 LEDs.

It gets a bit confusing for me when trying to use bytes in arrays with multiple shift registers and this is what I have scrounged together, I’ve already looked through and kinda derived my code from this tutorial:

Just to clarify, MY CODE WORKS but I am wondering if there is an easier/shorter way to do this (maybe I will want to use more than 2 shift registers one day):

int clockPin = 2;
int latchPin = 3;
int dataPin = 4;

byte firstEightLEDs[] = {1, 2, 4, 8, 16, 32, 64, 128, 0, 0, 0, 0, 0, 0, 0, 0, 0};
byte secondEightLEDs[] = {0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 4, 8, 16, 32, 64, 128, 0};

const int NUM_LED = 16;

void setup() {

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

}

void loop() {
  for (int i = 0; i < NUM_LED; i++) {

    digitalWrite(latchPin, LOW);
    shiftOut(dataPin, clockPin, MSBFIRST, firstEightLEDs[i]);
    shiftOut(dataPin, clockPin, MSBFIRST, secondEightLEDs[i]);
    digitalWrite(latchPin, HIGH);

    delay(500);
    
            //Array value 16 is 0 for both arrays... so it turns both off
    digitalWrite(latchPin, LOW);
    shiftOut(dataPin, clockPin, MSBFIRST, firstEightLEDs[16]);
    shiftOut(dataPin, clockPin, MSBFIRST, secondEightLEDs[16]);
    digitalWrite(latchPin, HIGH);

    delay(500);

  }
}

Just trying to pick your brains to see if I can understand this topic a bit better,
Much Appreciated

#2

For the example presented I'd use a 16-bit integer and just shift a one through using the for() loop. To separately access both bytes of the integer for transmission, create a union containing the 16-bit variable and a two-byte byte array.

You may find it useful to put the shift code into a function.

#3

marcussavery:
Hello all,
I'm trying to turn on and off an LED, then go to the next LED in line and do the same, with a for loop going through all outputs....

just to be clear, is this the pattern you want,
Capture.PNG

or this one?
Capture1.PNG

Capture1.PNG

Capture.PNG

#4

sherzaad:
just to be clear...

Good catch!

#5

There’s bit-bang way of doing it

void shift_out_16(uint16_t bb16)
{
	for(byte i = 0; i < 16; i++)
	{
		digitalWrite(dataPin, (bb16 & 1));
		digitalWrite(clockPin, 1);
		digitalWrite(clockPin, 0);
		bb16 >>= 1;
	}
	digitalWrite(latchPin, 1);
	digitalWrite(latchPin, 0);
}

You can put delays in wherever you want as the 595 is synchronous it won’t do anything prior to the clock/latch pins pulsing.

#6

sherzaad:
or this one?
Capture1.PNG

It would be the second one as there will be a time interval where all leds are off

#7

DKWatson:
There’s bit-bang way of doing it

dougp:
use a 16-bit integer and just shift a one through using the for() loop.

Used both of your advice and help and it ended up bringing down the ‘in loop’ code down to a few lines and makes more sense now, thanks

int clockPin = 2;
int latchPin = 3;
int dataPin = 4;
const int NUM_LED = 16;

int x = 1;

void setup() {
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
}

void loop() {
  for (int i = 0; i < NUM_LED; i++) {
    int result = x << i;

    shift_out_16(result);
    delay(200);
    shift_out_16(0);
    delay(200);
  }
}

void shift_out_16(uint16_t bb16)
{
  for (byte i = 0; i < 16; i++)
  {
    digitalWrite(dataPin, (bb16 & 1));
    digitalWrite(clockPin, 1);
    digitalWrite(clockPin, 0);
    bb16 >>= 1;
  }
  digitalWrite(latchPin, 1);
  digitalWrite(latchPin, 0);
}
#8

Google “C++ bit-shiftiing operator”.

In your code, [nobbc]firstEightLEDs[i][/nobbc] is exactly the same as the expression [nobbc]1 << i[/nobbc]

#9