shifter register

[juniorhowell]

i am attempting to get 8 leds to do a sweep with my arduino mega and an 74hc595n shifter regester after folling many tutorials and sample codes i get nothing.

Code: [Select]

int dataPin = 2;        //Define which pins will be used for the Shift Register control
int latchPin = 3;
int clockPin = 4;

int seq[14] = {1,2,4,8,16,32,64,128,64,32,16,8,4,2};       //The byte sequence

void setup()
{
    pinMode(dataPin, OUTPUT);       //Configure each IO Pin
    pinMode(latchPin, OUTPUT);
    pinMode(clockPin, OUTPUT);
}

void loop()
{
    for (int n = 0; n < 14; n++)
    {
        digitalWrite(latchPin, LOW);             //Pull latch LOW to start sending data
        shiftOut(dataPin, clockPin, MSBFIRST, seq[n]);          //Send the data
        digitalWrite(latchPin, HIGH);            //Pull latch HIGH to stop sending data
        delay(75);
    }
}

and i have the shift register connected to pins 2,3,4, but i get nothing out of it the code compiles to the board fine

[juniorhowell]

that is my wiring set up

[billroy]

Nothing jumps out as a problem.

Does it help if you set latchpin HIGH in setup()?

It might be worth operating the hardware side without the arduino attached -- jumper the latch pin low and the data pin high and wiggle the clock line by jumpering it to ground and +5 alternately…

-br
http://bitlash.net

[juniorhowell]

ok that makes sense and i think i have bad shift registers out of the ten i have none of them do the same thing when i run that test on just the hardware

[juniorhowell]

when i direct drive the matrix i have no problems my 595's must be duds

[MarkT]

You need decoupling on the 595, could easily be the problem.

[juniorhowell]

what do you mean by that?

[MarkT]

You are switching lots of current to the LEDs at fantastic speeds, if there's no decoupling capacitor close to the shift register the transients could reset the chip as it latches and make it look like its broken.  Every logic chip should have decoupling close-by (within a cm or so), 0.1uF as a minimum, for higher current loads 1uF or more could be wise.

You don't show decoupling in your diagram so I assumed you'd omitted it...

[ assume 8 times 20mA, thats upto 0.16A switching in 3ns or so, over 50 million amps/second -
  it doesn't take much stray inductance to induce several volts at those rates ]

[juniorhowell]

so a capicotor between the latch pin and ground?

[nickgammon]

Power and Gnd (VCC and Gnd).

[dhenry]

my 595's must be duds

One can go bad - I have yet to see a bad ic in my life, however. However, it is unlikely all of them have gone back.

Maybe the issue is your wiring?

If you have a logic analyzer / scope you can put it on the sck/mosi pins to see if the right sequency is actually piped to the chip.

[juniorhowell]

hmm i dont know i was just following a tutorial and its wiring diagram just to get a start on how the shift registers work and when i set it up it didnt work. So basically i am lost.

[juniorhowell]

my goal was to grasp the understanding of the shift register then move on to an 8x8 matrix with shift register.

[nickgammon]

See my page here:

http://www.gammon.com.au/forum/?id=11518

Also one about the 8x8 matrix:

http://www.gammon.com.au/forum/?id=11516

The decoupling capacitors (between Vcc and Gnd) will probably help. I found my shift registers behaved a bit strangely without them.

[MarkT]

hmm i dont know i was just following a tutorial and its wiring diagram just to get a start on how the shift registers work and when i set it up it didnt work. So basically i am lost.

Go and complain to the author of the tutorial!  Decoupling capacitors are essential...