Arduino Tutorial Bundle .:Arduino Experimentation Kit:. (ARDX)

Step 7: .:8 More Leds:. (74HC595 Shift Register) - CIRC05

What We're Doing:
Time to start playing with chips. Or integrated circuits (ICs) as they like to be called. The external packaging of a chip can be very deceptive for example the chip on the Arduino board (a micro controller) and the one we will use in this circuit (a shift register) look very similar but are in fact rather different, for example the price of the Atmega chip on the arduino board is a few dollars while the 74hc595 is a couple dozen cents. It's a good introductory chip, and once your comfortable playing around with it and its datasheet (available online http://tinyurl.com/pr42xe ) the world of chips will be your oyster. The shift register (also called a serial to parallel converter), will give you an additional 8 outputs (to control LEDs and the like) using only three arduino pins. They can also be linked together to give you a nearly unlimited number of outputs using the same four pins. To use it you clock in the data and then latch lock it in (latch it). To do this you set the data pin to either HIGH or LOW, pulse the clock, then set the data pin again and pulse the clock repeating until you have shifted out 8 bits of data. Then you pulse the latch and the 8 bits are transferred to the shift registers pins. It sounds complicated but is really simple once you get the hang of it.
(for a more in depth look at how a shift register works visit: http://tinyurl.com/56uvv7 )

(you can also download the breadboard layout sheet from the bottom of this step)


The Parts:

• CIRC-05 Breadboard sheet
• 2 Pin Header (x40
• Shift Register (74HC595) (x1)
• 560 ohm Resistor (green-blue-brown) (x8)
• 5mm Red LED (x8)
• Wire

The Circuit and Plugging Everything In:
A Small Video of Everything Being Plugged in

The Code: - http://tinyurl.com/cv4fjt

/*     ---------------------------------------------------------  *     |  Arduino Experimentation Kit Example Code             |  *     |  CIRC-05 .: 8 More LEDs :. (74HC595 Shift Register)   |  *     ---------------------------------------------------------  * * We have already controlled 8 LEDs however this does it in a slightly * different manner. Rather than using 8 pins we will use just three * and an additional chip. * * For more information on this circuit http://tinyurl.com/111111/ * *///Pin Definitions//The 74HC595 using a protocol called SPI (for more details http://www.arduino.cc/en/Tutorial/ShiftOut)//Which has three pinsint data = 2; int clock = 3;int latch = 4;//Used for single LED manipulationint ledState = 0;const int ON = HIGH;const int OFF = LOW;                        /* * setup() - this function runs once when you turn your Arduino on * We set the three control pins to outputs */void setup(){  pinMode(data, OUTPUT);  pinMode(clock, OUTPUT);    pinMode(latch, OUTPUT);  }/* * loop() - this function will start after setup finishes and then repeat * we set which LEDs we want on then call a routine which sends the states to the 74HC595 */void loop()                     // run over and over again{  int delayTime = 100; //the number of milliseconds to delay between LED updates  for(int i = 0; i < 256; i++){   updateLEDs(i);   delay(delayTime);   }}/* * updateLEDs() - sends the LED states set in ledStates to the 74HC595 * sequence */void updateLEDs(int value){  digitalWrite(latch, LOW);     //Pulls the chips latch low  shiftOut(data, clock, MSBFIRST, value); //Shifts out the 8 bits to the shift register  digitalWrite(latch, HIGH);   //Pulls the latch high displaying the data}/* * updateLEDsLong() - sends the LED states set in ledStates to the 74HC595 * sequence. Same as updateLEDs except the shifting out is done in software * so you can see what is happening. */ void updateLEDsLong(int value){  digitalWrite(latch, LOW);    //Pulls the chips latch low  for(int i = 0; i < 8; i++){  //Will repeat 8 times (once for each bit)  int bit = value & B10000000; //We use a "bitmask" to select only the eighth                                //bit in our number (the one we are addressing this time through  value = value << 1;          //we move our number up one bit value so next time bit 7 will be                               //bit 8 and we will do our math on it  if(bit == 128){digitalWrite(data, HIGH);} //if bit 8 is set then set our data pin high  else{digitalWrite(data, LOW);}            //if bit 8 is unset then set the data pin low  digitalWrite(clock, HIGH);                //the next three lines pulse the clock pin  delay(1);  digitalWrite(clock, LOW);  }  digitalWrite(latch, HIGH);  //pulls the latch high shifting our data into being displayed}//These are used in the bitwise math that we use to change individual LEDs//For more details http://en.wikipedia.org/wiki/Bitwise_operationint bits[] = {B00000001, B00000010, B00000100, B00001000, B00010000, B00100000, B01000000, B10000000};int masks[] = {B11111110, B11111101, B11111011, B11110111, B11101111, B11011111, B10111111, B01111111};/* * changeLED(int led, int state) - changes an individual LED  * LEDs are 0 to 7 and state is either 0 - OFF or 1 - ON */ void changeLED(int led, int state){   ledState = ledState & masks[led];  //clears ledState of the bit we are addressing   if(state == ON){ledState = ledState | bits[led];} //if the bit is on we will add it to ledState   updateLEDs(ledState);              //send the new LED state to the shift register }  

And upload this will cause the lights to light up one after another and then off in a similar manner. Check the code and wikipedia to see how it works, or shoot us an e-mail if you have questions.

More Animations:
Now things get more interesting. If you look back to the code from CIRC02 (8 LED Fun) you see we change the LEDs using digitalWrite(led, state), this is the same format as the routine we wrote changeLED(led, state). You can use the animations you wrote for CIRC02 by copying the code into this sketch and changing all the digitalWrite()'s to changeLED()'s. Powerful? Very. (you'll also need to change a few other things but follow the compile errors and it works itself out)

Comments

[mwagner5]

Hello,

I was reading the datasheet of the 74HC595 and I came across with some values...

It is written that the max Icc/Ignd is 70mA, and each output pin supports 35mA.
If I want, for example, lit 8 leds at the same time, each at 20mA, the total would be 160mA.

So, wouldnt it damage the 74HC595?


Thanks a lot

[DrJoMaVa]

Hello,
This step mentions linking multiple shift registers together to control a larger number of LEDs with just 4 Arduino pins. How is this accomplished? Thanks for your help.

[md81544]

http://www.arduino.cc/en/Tutorial/ShiftOut

[Rencio7]

 LEDs are around the wrong way on the left side of the diagram - I think -Im new to this stuff -I. :(  it was a bit annoying testing each part of the circuit - and matching it up to a wrong diagram..

[Rencio7]

 *make that both sides :P yay it works !

[Splooshiba]

 i just got my arduino and have been playing with the code, but with no luck. What is the output from this code with NO changes made what so ever. 

Where do changes need to be made to change the LEDs which light. Advice would be much appreciated, many thanks.

[pben]

On LEDs the long lead (metal leg) is the Anode (+) and the flat side of package at the base of the dome is the cathode (-).  The diagram for CIRC-01 has that reversed. 

The Anode and Cathode names are a hold over from the old days when diodes were vacuum tubes (valves for you Europeans out there).   Good news no damage will be done if they are put in backwards on this circuit.  It will jest not light the LED but the on-board LED will still flash.