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

The 74HC595 is an 8-bit shift register with an output latch, designed for serial-to-parallel data conversion. It enables microcontrollers to control multiple outputs using only a few pins, making it an essential component in projects requiring efficient pin usage. The 74HC595 features a serial input, parallel output, and the ability to cascade multiple chips to expand the number of outputs. This makes it ideal for applications such as LED displays, motor control, and other scenarios where multiple outputs need to be controlled simultaneously.

• Driving LED arrays or 7-segment displays
• Expanding GPIO pins on microcontrollers
• Controlling relays or other digital outputs
• Building cascaded shift register circuits for large-scale output control

The 74HC595 is a high-speed CMOS device with the following key specifications:

The 74HC595 comes in a 16-pin DIP/SOIC package. Below is the pinout and description:

1. Power the Chip: Connect the Vcc pin to a 5V or 3.3V power supply (depending on your system) and GND to ground.
2. Connect Control Pins:
   • Connect SH_CP (Shift Clock) and ST_CP (Latch Clock) to GPIO pins on your microcontroller.
   • Connect DS (Serial Data Input) to the data pin of your microcontroller.
   • Optionally, connect OE to ground to enable outputs or to a GPIO pin for dynamic control.
3. Load Data:
   • Send serial data to the DS pin, synchronized with the SH_CP clock.
   • Use the ST_CP pin to latch the data into the output register.
4. Cascading:
   • To cascade multiple 74HC595 chips, connect the Q7' pin of the first chip to the DS pin of the next chip.
   • Share the SH_CP and ST_CP pins across all chips.

• Use decoupling capacitors (e.g., 0.1 µF) between Vcc and GND to stabilize the power supply.
• Avoid exceeding the maximum current rating of 6 mA per output pin.
• Use pull-down resistors on unused input pins to prevent floating states.

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

// Define 74HC595 control pins
const int dataPin = 2;  // DS (Serial Data Input)
const int latchPin = 3; // ST_CP (Latch Clock)
const int clockPin = 4; // SH_CP (Shift Clock)

// Binary pattern to display on LEDs
byte ledPattern = 0b10101010;

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

void loop() {
  // Send data to the 74HC595
  digitalWrite(latchPin, LOW); // Disable latch to load data
  shiftOut(dataPin, clockPin, MSBFIRST, ledPattern); // Send data
  digitalWrite(latchPin, HIGH); // Enable latch to update outputs

  delay(500); // Wait for 500ms
  ledPattern = ~ledPattern; // Invert pattern for next cycle
}

• The shiftOut function sends data serially to the 74HC595.
• The latchPin ensures that the data is only displayed after it is fully loaded.
• The ledPattern variable determines which LEDs are ON or OFF.

1. Outputs Not Responding:
   • Ensure the OE pin is connected to ground or properly controlled.
   • Verify that the ST_CP and SH_CP pins are receiving clock signals.
2. Incorrect Output States:
   • Check the data being sent to the DS pin.
   • Ensure the latchPin is toggled after data is shifted in.
3. Cascaded Chips Not Working:
   • Verify the connection between the Q7' pin of one chip and the DS pin of the next.
   • Ensure all chips share the same clock and latch signals.

Q: Can I use the 74HC595 with a 3.3V microcontroller?
A: Yes, the 74HC595 operates with supply voltages as low as 2V, making it compatible with 3.3V systems.

Q: How many 74HC595 chips can I cascade?
A: Theoretically, you can cascade as many as needed, but practical limits depend on signal integrity and timing constraints.

Q: What happens if I don't connect the OE pin?
A: The outputs will remain disabled. Connect OE to ground to enable the outputs.

Q: Can the 74HC595 drive high-power devices like motors?
A: No, the 74HC595 can only source/sink up to 6 mA per pin. Use external drivers or transistors for high-power devices.