How to Use HEF4094: Examples, Pinouts, and Specs

The HEF4094 is an integrated circuit that functions as an 8-bit serial-in, serial or parallel-out shift register. This component is particularly useful in applications where there is a need to expand the number of output pins available on a microcontroller, such as the Arduino UNO. It allows for the control of multiple devices using a minimal number of I/O pins by shifting data serially into the register and then outputting it in either a serial or parallel format. Common applications include driving LEDs, LCDs, and other digital devices in a variety of electronic projects.

• Supply Voltage (Vcc): 3 V to 15 V
• Clock Frequency (Max): 25 MHz at Vcc = 15 V
• Output Current (Max per Pin): 25 mA
• Operating Temperature Range: -40°C to +85°C
• Package Type: Available in SO16 and DIP16 packages

1. Power Supply: Connect pin 16 (Vcc) to the positive supply voltage (3 V to 15 V) and pin 8 (GND) to the ground.
2. Data Input: Apply the serial data to pin 13 (DATA) that you want to shift into the register.
3. Clocking Data: Apply a clock signal to pin 14 (CLK) to shift the data into the register.
4. Output Enable: To enable the outputs, connect pin 11 (/OE) to ground. If you wish to disable the outputs, apply a high signal to this pin.
5. Strobe Input: Use pin 12 (ST_CP) to transfer data from the shift register to the storage register. This allows for parallel output on pins Q0 to Q7.
6. Cascading Units: If more than 8 bits are required, the serial output on pin 1 (Q7') can be connected to the serial data input of the next HEF4094.

• Ensure that the supply voltage does not exceed the maximum rating of 15 V to prevent damage to the IC.
• It is recommended to use a decoupling capacitor (e.g., 0.1 µF) between Vcc and GND near the IC to filter out noise.
• Avoid floating inputs by connecting unused pins to a defined logic level.
• When cascading multiple HEF4094 ICs, ensure that the clock and strobe signals are distributed uniformly to all ICs.

// Define the pins connected to the HEF4094
const int dataPin = 2;    // HEF4094 Pin 13 - DATA
const int clockPin = 3;   // HEF4094 Pin 14 - CLK
const int strobePin = 4;  // HEF4094 Pin 12 - ST_CP

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

void loop() {
  // Example: shift out the number 255 (binary 11111111)
  shiftOut(dataPin, clockPin, MSBFIRST, 255);
  // Strobe the register to output the data
  digitalWrite(strobePin, HIGH);
  delay(1); // Wait for a moment
  digitalWrite(strobePin, LOW);
  delay(1000); // Wait for a second
}

// Note: The above code assumes that /OE is connected to GND

• No Output on Pins Q0-Q7: Ensure that /OE is connected to ground and that the ST_CP pin has been pulsed high after data is clocked in.
• Inconsistent Output: Check for loose connections and ensure that the clock signal is clean and free of noise.
• Unexpected Behavior When Cascading: Verify that the Q7' of one IC is correctly connected to the DATA input of the next IC and that all ICs receive the same clock and strobe signals.

• Use an oscilloscope to check the clock and data signals for integrity.
• Ensure that the power supply is stable and within the specified voltage range.
• If using long wires or cables, consider the effects of capacitance and electromagnetic interference on signal quality.

Q: Can the HEF4094 be used with a 5V Arduino? A: Yes, the HEF4094 can operate at 5V, making it compatible with 5V microcontrollers like the Arduino UNO.

Q: How do I reset the HEF4094? A: The HEF4094 does not have a dedicated reset pin. To reset, you can clear the register by shifting in zeros and strobing the output.

Q: Can I use the HEF4094 to drive power-hungry devices? A: The HEF4094 can source or sink up to 25 mA per pin. For devices requiring more current, use a transistor or a driver IC to amplify the current.