How to Use SHIFT REGISTER: Examples, Pinouts, and Specs

The 74*595 is an 8-bit serial-in, parallel-out shift register with a storage register and tri-state outputs. It is widely used in digital electronics to expand the number of output pins available on a microcontroller or microprocessor. By cascading multiple shift registers, users can control a large number of outputs using only a few pins.

• Driving LED arrays or 7-segment displays
• Expanding GPIO pins on microcontrollers
• Controlling relays or other digital outputs
• Data storage and transfer in digital circuits
• Multiplexing and demultiplexing signals

The 74*595 shift register is a versatile component with the following key specifications:

The 74*595 has 16 pins, as described in the table below:

The 74*595 shift register is easy to use in digital circuits. Below are the steps and considerations for using it effectively:

1. Power Supply: Connect the Vcc pin to a 5V or 3.3V power source (depending on your system) and the GND pin to ground.
2. Data Input: Connect the DS pin to the microcontroller's data output pin.
3. Clock Pins:
   • Connect the SH_CP pin to a microcontroller pin for the shift clock.
   • Connect the ST_CP pin to another microcontroller pin for the storage clock.
4. Outputs: Connect the Q0-Q7 pins to the desired output devices (e.g., LEDs, relays).
5. Optional: If cascading multiple shift registers, connect the Q7' pin of the first register to the DS pin of the next register.

Below is an example of how to connect and control the 74*595 with an Arduino UNO to drive 8 LEDs:

• Connect the 74*595's Vcc to the Arduino's 5V pin and GND to GND.
• Connect the DS pin to Arduino pin 11.
• Connect the SH_CP pin to Arduino pin 12.
• Connect the ST_CP pin to Arduino pin 8.
• Connect LEDs to Q0-Q7 through 220-ohm resistors.

// Define pins for the 74*595 shift register
const int dataPin = 11;  // DS pin of 74*595
const int clockPin = 12; // SH_CP pin of 74*595
const int latchPin = 8;  // ST_CP pin of 74*595

void setup() {
  // Set pins as outputs
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
}

void loop() {
  // Example pattern to display on LEDs
  for (int i = 0; i < 256; i++) {
    digitalWrite(latchPin, LOW); // Disable storage register updates
    shiftOut(dataPin, clockPin, MSBFIRST, i); // Send data to shift register
    digitalWrite(latchPin, HIGH); // Update storage register to display data
    delay(500); // Wait for 500ms
  }
}

• Use pull-down resistors on unused input pins to prevent floating states.
• Add decoupling capacitors (e.g., 0.1 µF) near the Vcc and GND pins to reduce noise.
• Avoid exceeding the maximum current rating of the outputs to prevent damage.
• When cascading multiple shift registers, ensure the clock signals are synchronized.

1. LEDs Not Lighting Up:
   • Check the wiring and ensure the LEDs are connected with the correct polarity.
   • Verify that the resistors are of appropriate value (e.g., 220 ohms).
2. Shift Register Not Responding:
   • Ensure the Vcc and GND pins are properly connected.
   • Verify that the clock and data signals are being sent correctly from the microcontroller.
3. Incorrect Output Pattern:
   • Check the timing of the SH_CP and ST_CP signals.
   • Ensure the data is being shifted in the correct order (MSB or LSB first).

Q1: Can I cascade multiple 74*595 shift registers?
Yes, you can cascade multiple shift registers by connecting the Q7' pin of one register to the DS pin of the next. This allows you to control more outputs with the same microcontroller.

Q2: What is the purpose of the OE pin?
The OE (Output Enable) pin is used to enable or disable the parallel outputs. When OE is high, the outputs are in a high-impedance state.

Q3: Can the 74*595 drive high-power devices?
No, the 74*595 is not designed to drive high-power devices directly. Use external transistors or MOSFETs for high-power applications.

Q4: What is the difference between SH_CP and ST_CP?

• SH_CP (Shift Clock) is used to shift data into the register.
• ST_CP (Storage Clock) is used to transfer the shifted data to the output latches.

By following this documentation, you can effectively use the 74*595 shift register in your projects!