SPI and TPIC6c595

Using Arduino LEDs and Multiplexing
#1

Trying to test/learn SPI and shift registers via a simple “knight rider” LED sweep, but instead of sweeping, the LEDs light either one or two at a time from 0 to 7 in a loop.
8 LEDs driven by a TPIC6c595 / Uno.
Is my byte output correct?

#include <SPI.h>


const byte scanArray[] = {
0b00000001,
0b00000010,
0b00000100,
0b00001000,
0b00010000,
0b00100000,
0b01000000,
0b10000000,
0b01000000,
0b00100000,
0b00010000,
0b00001000,
0b00000100,
0b00000010,
0b00000001
};

const int dataPin = 11;
const int latchPin = 13;
const int slaveSelectPin = 10; 

int index = 0;

void setup() {
  pinMode(dataPin, OUTPUT);  
  pinMode(latchPin, OUTPUT);
  pinMode (slaveSelectPin, OUTPUT);
  Serial.begin(9600);
  SPI.begin();
  digitalWrite(slaveSelectPin,LOW);
  
}

void loop() {
if (index<10){
    delay(200);
    digitalWrite (slaveSelectPin, LOW);
    SPI.transfer (scanArray[index]); 
    digitalWrite (slaveSelectPin, HIGH);
    index++;
  }
index=0;
}
#2

You have a logic error. Index will always be 0 when tested by your if statement. You need a for or while statement instead of an if statement to cycle through all the values of that index should take on (0 to 14).

#3

Agreed with Mrs. Cross Roads. Also, you could do this, which is closer I think to your intent:

oracledude:

void loop() {

if (index<15){
    delay(200);
    digitalWrite (slaveSelectPin, LOW);
    SPI.transfer (scanArray[index]);
    digitalWrite (slaveSelectPin, HIGH);
    index++;
  }
  else
    index=0;
}

I changed the top count to 14 here. You have 15 indices - 0 to 15 in your array.

#4

Take these out - they interfere with SPI library.

const int dataPin = 11;
const int latchPin = 13;
pinMode(dataPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
#5

Well, that's a pain in the butt! Darn forum stuck in a bunch of codes on me, and won't let me edit them?

#6

And wiped out my simple for loop! Arrgh.
Which JoeN has, just not written as a for loop.

#7

No dice. Updated the code and the LEDs still go one way only. Each iteration is different from the last though. one time through it lights 0,1/2,3/4,5/6,7. Next cycle its 0,1/2,2/3,3/4,5/6,6/7.

#include <SPI.h>


const byte scanArray[] = {
0b00000001,
0b00000010,
0b00000100,
0b00001000,
0b00010000,
0b00100000,
0b01000000,
0b10000000,
0b01000000,
0b00100000,
0b00010000,
0b00001000,
0b00000100,
0b00000010,
0b00000001
};

//const int dataPin = 11;
//const int latchPin = 13;
const int slaveSelectPin = 10; 

int index = 0;

void setup() {
  // set the Pins as output:
//  pinMode(dataPin, OUTPUT);  
//  pinMode(latchPin, OUTPUT);
  pinMode (slaveSelectPin, OUTPUT);
  Serial.begin(9600);
  // initialize SPI:
  SPI.begin();
  // take the SS pin low to select the chip:
  digitalWrite(slaveSelectPin,LOW);
  
}

void loop() {
//for (int i=0; i <= 10; i++){
  if (index<15){
    delay(200);
    digitalWrite (slaveSelectPin, LOW);
    SPI.transfer (scanArray[index]); 
    digitalWrite (slaveSelectPin, HIGH);
    index++;
  }
  else
    index=0;
}
#8

Switched Data and Latch pins and it works. Thanks for the help!

Now onto ShiftPWM. :slight_smile:

#9

oracledude:
Switched Data and Latch pins and it works. Thanks for the help!

Now onto ShiftPWM. :slight_smile:

Good, ya scared me there for a second. :slight_smile:

#10