Shift registers

Using Arduino LEDs and Multiplexing
1

Hi my project is based on http://www.arduino.cc/en/Tutorial/ShiftOut and Overview | Arduino Lesson 4. Eight LEDs and a Shift Register | Adafruit Learning System.

What I have is the board set up like in the Shift Out tutorial just with 7 led's per shift register instead of 8 that is shown in the tutorial.

As for code what I have for now is:

int latchPin = 8;
int clockPin = 12;
int dataPin = 11;
 
byte leds = 0;
 
 
int firstSet = 1;

int secondSet = 2;
 
void setup() 
{
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);  
  pinMode(clockPin, OUTPUT);
}
 
void loop() 
{
  leds = 0;  
//For first set of (red) leds / first shift register
if(firstSet==1)
{
disleds0();
}
else if(firstSet==2)
{
  disleds1();
}
else if(firstSet==3)
{
  disleds2();
}

//For second set of (green) leds / second shift register
if(secondSet==1)
{
disleds0SS();
}
else if(secondSet==2)
{
  disleds1SS();
}
else if(secondSet==3)
{
  disleds2SS();
}

}
 
void updateShiftRegister()
{
   digitalWrite(latchPin, LOW);
   shiftOut(dataPin, clockPin, LSBFIRST, leds);
   digitalWrite(latchPin, HIGH);
}



void disleds0()
{
  bitSet(leds, 0);  //if firstSet == 1 light up the first led
    updateShiftRegister();
}
void disleds1()
{
  bitSet(leds, 1); //if firstSet == 2 light up the second led
    updateShiftRegister();
}
void disleds2()
{
  bitSet(leds, 2); //if firstSet == 3 light up the third led
    updateShiftRegister();
}



void disleds0SS()
{
  bitSet(leds, 0); //if secondSet == 1 light up the first led on the second shift register
    updateShiftRegister();
}
void disleds1SS()
{
  bitSet(leds, 1); //if secondSet == 2 light up the second led on the second shift register
    updateShiftRegister();
}
void disleds2SS()
{
  bitSet(leds, 2); //if secondSet == 3 light up the third led on the second shift register
    updateShiftRegister();
}

(I left out some of the repeating code to make the code easier to read.)

So the problem is that when I run the code with firstSet = 1 and secondSet = 2 the first two led's for both sets of led's are lighting up when in this case I would only want the first led to light on the first set of led's / shift register and for only the second led on the second set of led's / second shift register.

In more straight forward way how do I send specific data to each shift register.
(as far as I know i have to send a second shift out, I think, I just don't know how to do it. )

Thanks in advance.

2
  1. Get rid of the cap.
  2. Put a 0.1uF cap from each device's Vcc pin to Gnd.
  3. Fix your code to output 2 bytes every time you want the output updated.
void updateShiftRegister()
{
   digitalWrite(latchPin, LOW);
   shiftOut(dataPin, clockPin, LSBFIRST, leds1);
   shiftOut(dataPin, clockPin, LSBFIRST, leds2);
   digitalWrite(latchPin, HIGH);
}

and keep the data you are sending out in leds1 and leds2

3

Thanks a lot I still have to test all the details but as far as I can tell this is working as planed.
Thank you so much.

4