How to Use 74HC595: Examples, Pinouts, and Specs

The 74HC595 is an 8-bit serial-in, parallel-out shift register with an output latch, manufactured by Arduino under the part ID "UNO". This component is widely used for serial-to-parallel data conversion, allowing users to control multiple output pins using only a few input pins. It is particularly useful in applications where microcontroller I/O pins are limited, such as LED matrix displays, seven-segment displays, and data storage systems.

By cascading multiple 74HC595 chips, users can expand the number of output pins even further, making it a versatile solution for projects requiring a large number of outputs.

The following table outlines the key technical details of the 74HC595:

The 74HC595 has 16 pins, as described in the table below:

1. Power the Chip: Connect the Vcc pin (16) to a 5V power supply and the GND pin (8) to ground.
2. Connect Control Pins:
   • Connect the DS pin (14) to the microcontroller's data output pin.
   • Connect the SH_CP pin (11) to the microcontroller's clock pin.
   • Connect the ST_CP pin (12) to the microcontroller's latch pin.
3. Load Data:
   • Send serial data to the DS pin while pulsing the SH_CP pin to shift the data into the register.
   • Pulse the ST_CP pin to latch the data into the output register.
4. Enable Outputs: Ensure the OE pin (13) is connected to ground to enable the outputs.

• Use current-limiting resistors on the output pins when driving LEDs to prevent damage to the chip.
• If cascading multiple 74HC595 chips, connect the Q7' pin (9) of the first chip to the DS pin (14) of the next chip.
• Keep the clock signal clean and free of noise to ensure proper data shifting.
• Use decoupling capacitors (e.g., 0.1 µF) between Vcc and GND to stabilize the power supply.

Below is an example of how to use the 74HC595 with an Arduino UNO to control 8 LEDs:

// Define the 74HC595 control pins
const int dataPin = 2;  // DS pin (14) connected to Arduino pin 2
const int clockPin = 3; // SH_CP pin (11) connected to Arduino pin 3
const int latchPin = 4; // ST_CP pin (12) connected to Arduino pin 4

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

void loop() {
  // Example pattern to display on LEDs
  byte ledPattern = 0b10101010; // Alternating LEDs on/off

  // Send the pattern to the 74HC595
  digitalWrite(latchPin, LOW); // Disable latch
  shiftOut(dataPin, clockPin, MSBFIRST, ledPattern); // Send data
  digitalWrite(latchPin, HIGH); // Enable latch

  delay(500); // Wait for 500ms
}

• The shiftOut function sends 8 bits of data to the 74HC595, starting with the most significant bit (MSBFIRST).
• The latchPin is toggled to transfer the shifted data to the output pins.
• The ledPattern variable defines which LEDs are turned on or off.

1. Outputs Not Responding:

   • Ensure the OE pin (13) is connected to ground.
   • Verify that the ST_CP pin (12) is being pulsed after shifting data.

2. Incorrect Output Pattern:

   • Check the order of bits in the data being sent (MSB vs. LSB).
   • Ensure the clock signal is stable and matches the timing requirements.

3. Chip Overheating:

   • Verify that the output current does not exceed 35 mA per pin.
   • Use appropriate resistors for LEDs or other loads.

Q: Can I cascade multiple 74HC595 chips?
A: Yes, connect the Q7' pin (9) of the first chip to the DS pin (14) of the next chip. Repeat for additional chips.

Q: What is the purpose of the OE pin?
A: The OE pin enables or disables all outputs. When high, all outputs are in a high-impedance state.

Q: Can the 74HC595 drive motors directly?
A: No, the 74HC595 cannot handle the high current required by motors. Use a motor driver circuit instead.