Arduino Nano, ICSP header and 595 Shift register

Question

I'm trying to control a 4-digit 7 segment display with an Arduino Nano, but I'm getting something wrong. I'm using the ICSP header to interface with a 74HC595 Shift Register which is then connected to the display. I've tested and retested the connections and everything seems to be alright, however the shift register doesn't have the desired output, and I notice it only shifs one single bit when I press the reset button on the arduino board.

74HC595 | A. Nano
DS <-----> MOSI (ICSP)
SH_CP <-----> SCK (ICSP)
ST_CP <-----> D6
MR <-----> 5V (ICSP)
OE <-----> GND (ICSP)
VDD <-----> 5V (ICSP)
GND <-----> GND (ICSP)

My code:

//pin connected to STCP
const int latchPin = 6;
//pin connected to SHCP
const int clockPin = 17;
//pin connected to DS (MOSI)
const int dataPin = 11;
byte val=0;
void setup() {
 // put your setup code here, to run once:
 //SPI pins are output
 pinMode(latchPin,OUTPUT);
 pinMode(clockPin,OUTPUT);
 pinMode(dataPin,OUTPUT);
 pinMode(3,OUTPUT);
 updateRegister(0);
}
void loop() {
 // put your main code here, to run repeatedly:
 digitalWrite(3,HIGH); 
 for (int i=0; i<8; i++) {
 updateRegister();
 delay(500);
 } 
}
void updateRegister() {
 //pull latch low to write new bits to the register
 digitalWrite(latchPin,LOW);
 //shift out the data
 shiftOut(dataPin,clockPin,LSBFIRST,val);
 //pull latch pin high so that the leds light up
 digitalWrite(latchPin,HIGH);
}

• Nick Gammon: This site has a question and answer format. What is your question, exactly? (Note that questions generally end with a question mark). Please read How do I ask a good question?
• Nick Gammon: Please post a schematic of your wiring. You say in the question that you are using the ICSP header, but then the code uses pins 6 and 17 which are not ICSP (or SPI) pins.

Answer 1

const int clockPin = 17;

I'm pretty sure that should be 13, not 17.

• joaocandre: Yup, this was my mistake. christianto.tjahyadi.com/wp-content/uploads/2014/11/nano.jpg this image mislead me to believe SPI clock was at pin 17. With pin 13, the display is operating as it should.

Answer 2

It is extremely confusing to have a variable val and then use _val in your function but then:

 shiftOut(dataPin,clockPin,LSBFIRST,val);

As James pointed out, you are not sending the value passed to the function, to the shift register.

Also this is just going to give you a boolean:

 updateRegister(!i);

Why take "not i" there?

---

I suggest you use SPI and not muck around with shiftOut. I have a page about the 595 chip including example code. eg.

#include <SPI.h>
const byte LATCH = 10;
void setup ()
{
 SPI.begin ();
} // end of setup
byte c;
void loop ()
{
 c++;
 digitalWrite (LATCH, LOW);
 SPI.transfer (c);
 digitalWrite (LATCH, HIGH);
 delay (20);
} // end of loop

• joaocandre: I posted the code with some errors (I was paying with the varaibles trying to solve the problem). As it was it was bovisously not going to work, but that was not the cause of the problem. I tried that snippet with the SPI library, but the display/leds do not light up at all. Also, it just crossed my mind - could the problem be caused by calling shiftOut() on SPI pins?
• Nick Gammon: What LEDs exactly?
• Nick Gammon: could the problem be caused by calling shiftOut() on SPI pins? - No. If you don't call SPI.begin() then SPI is inactive.
• joaocandre: The leds on the 7-segment display

Answer 3

Do you need to add the _ to the shiftOut(dataPin,clockPin,LSBFIRST,val); ?

• Nick Gammon: James, you were right about the underscore, but the Stack Exchange system automatically flags very short answers. If you expand it out a bit more you are protected from this automated flagging. Welcome to Arduino Stack Exchange. :)
• joaocandre: It was a mistake, I was tinkering with the code. I've updated the question, but I can say that was not the source of the problem.
• Nick Gammon: Your updated code sends 0 to the shift register, so I'm not too surprised nothing lights up.
• joaocandre: The 7-segment display has a common anode, sending a '0' to the shift register should light up all the segments (an '8'), since I'm pulling the anode up with 'digitalWrite(3,HIGH); '