74HC595 Chips Counting In Binary

Forum 2005-2010 (read only) Hardware Interfacing
1

I wired up two 74HC595 chips with 16 LEDs, and wrote some simple code. They are counting in binary... How do I change this?

int dataPin = 13;
int latchPin = 12;
int clockPin = 11;

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

void loop()
{
 digitalWrite(latchPin, LOW);
 shiftOut(dataPin, clockPin, MSBFIRST, 4);
 shiftOut(dataPin, clockPin, MSBFIRST, 3);
 delay(10);
 digitalWrite(latchPin, HIGH);  
}
2

Use this instead:

 shiftOut(dataPin, clockPin, MSBFIRST, 1<<3);
 shiftOut(dataPin, clockPin, MSBFIRST, 1<<2);

1<<0 = 00000001
1<<1 = 00000010
1<<2 = 00000100

etc.

3

Ok, it works. I realised that I have to add that 1 to my other number. As in 1<<5 is light 6, ect. Thanks! :slight_smile:

4

Well... in the code you posted you sent the numbers 4 and 3 to the shift registers. As you said they 'counted in binary' I assume you wanted to light up the 4th and 3rd LED on the chips, which should work for 4, but not for 3.

Just replace 4 with 1<<3 and so on. '<<' is a bit shift operator which shifts the content of a byte n-bits to the left. In this example 1 is shifted 3 times to the left, resulting in the 4th LED lighting up.

Edit: seems you've found that one out already.

5

So how would I do no lights on?

6

You'll have to zero in on that one yourself :wink:

7

We'll give you ZERO help on that one whatsoever.

Sorry I can't resist a punny reponse.

8

LOL! I guess I would do a 9? As in 1<<8???

9

Well, I'm not 100% positive on that, but 1<<8 might be automatically promoted to a 16bit variable. What ShiftOut does with that one I don't know.

10

What ShiftOut does with that one I don't know.

It shifts out only a byte so if you do this you get nothing.
http://www.arduino.cc/en/Reference/ShiftOut

11

So it's a good thing I don't use ShiftOut :wink:

Apart from me not knowing about its endian-ness, it is too slow for any serious PWM jobs anyway.