How to use 74HC595 Shift Register and interface with Arduino? [FAQ]

The 74HC595 is a shift register that uses the Serial IN Parallel OUT protocol to operate. It receives serial data from the microcontroller before sending it out through parallel pins. Using a single chip, we may expand our output pins by eight.

The 74HC595 shift register has two main registers  :

• The shift register

• The output register  (or data latch or sometimes called a register latch  ).

The following is the internal structure of IC 74HC595  :

74HC595 Structurer

The 74HC595 shift register is designed in such a way that when the shift register data is updated using the serial clock (SRCLK) and serial data (SER) inputs, the chip's outputs remain unchanged. In other words, you can send data into the shift register and it will ripple through without changing the state of the output pins. The data is sent from the shift register to the output pins only when the output data clock (latch clock or register clock - RCLK) is strobed.

When a large number of devices must be interfaced with a microcontroller, the shift register is primarily utilized to overcome the microcontroller's pin shortage. The shift register changes data from one bit to the next in response to the register's clock pulses, and the data it shifts is stored in the register. The shift register has three major pins: one for the clock, another for the latch, and a third for the data.

74HC595 Pinout

In the table below, the pin configuration of a single shift register (74HC595) is shown:

Because every microcontroller has a limited number of  I/O  pins.  Shift registers are frequently utilized to save pins on the microcontroller  (GPIO).

If you want to control 16 individual LEDs with your project, you'll need an Arduino with 16  pins,  This is where the shift register comes in handy if you don't have 16 I/O pins accessible. We can control 16 LEDs with only three I/O pins by connecting two shift registers in series. Not only that, but the more shift registers you chain together, the more pins you save.

The 74HC595 Shift Register IC or any similar shift register for that matter can be used in the following applications:

• LED Control

• Network Switches

• Servers

• Power Infrastructure

•  Industrial Control

• Electronic Appliances

• Simple Serial-to-Parallel Data Conversion

• Capture and Hold Logic

Pins 11 (clock input), 12 (storage register clock input or just the latch input  ) and 14 (shift register clock input or simply the latch input  ) are the three pins of the shift register that must be connected to Arduino  (the data input).

The shift register IC will be connected to all 8 LEDs. (See the circuit design section for further information.)

Components Required:

• Arduino UNO

• 74HC595 Shift Register IC 

• Breadboard

• 8 X LEDs

• 8 X 1KΩ Resistors

• 5V Power Supply

• Connecting Wires

Circuit Diagram

We can begin connecting the 74HC595  to our Arduino now that we have a good idea of how it works!

Begin by inserting the shift register on your breadboard, making sure that each side of the IC is on its own side. The pins are 1-8 along the left-hand side from top to bottom with the little U-shaped notch facing upwards, and 16–9 down the right-hand side from top to bottom with the little U-shaped notch facing upwards.

Let's start by connecting pins 16 (VCC) and 10 (SRCLR) to the Arduino's 5v pin, and pins 8 (GND) and 13 (OE) to the Arduino's GND pin. This should keep the IC in its normal state of operation.

The three pins that will control the shift register must then be connected:

Pin 11 (SRCLK) of the shift register to pin 6 on the Arduino  

Pin 12 (RCLK) of the shift register to pin 5 on the Arduino

Pin 14 (SER) of the shift register to pin 4 on the Arduino

Now, all we have to do is connect all of the output pins to our LEDs, making sure that a 220 resistor is placed in front of the LEDs to limit current and that the LEDs' cathodes are connected to the ground.

Make sure the LEDs are wired in the correct order when installing them, with QA linked to the first LED and QH connected to the last, else our code will not light up the LEDs in the correct order!

The following is the circuit diagram of the 74HC595 shift register with Arduino:

 74HC595 shift register circuit

The shift register 74HC595 features two registers (sometimes known as "memory containers"), each of which holds just 8 bits of data. The first is referred to as the Shift Register,  Deep within the IC circuitry, the Shift Register discreetly accepts input.

When we give a 595 a clock pulse, two things happen:

The bits in the Shift Register shift to the left one step. For example, Bit 7 accepts the value from Bit 6, Bit 6 accepts the value from Bit 5, and so on.

The current value on the DATA pin is accepted by Bit 0 in the  Shift Register. If the data pin is high on the rising edge of the pulse, a 1 is pushed into the shift register. Otherwise, it's a 0 score.

The contents of the Shift Register are copied into the second register, the Storage/Latch Register, when the Latch pin is enabled. Because each bit of the Storage Register is connected to one of the IC's output pins QA–QH, the outputs change as the value in the Storage Register changes.