How to Use Multiplexer: Examples, Pinouts, and Specs

A multiplexer, often abbreviated as "MUX," is an electronic component that selects one of several input signals and forwards the selected input to a single output line. The 74HC151N, manufactured by Mani, is a high-speed CMOS 8-to-1 multiplexer. It is widely used in digital circuits for data routing, signal selection, and switching applications. This component is particularly useful in scenarios where multiple data sources need to be transmitted over a single communication line.

• Data selection and routing in digital systems
• Signal multiplexing in communication systems
• Memory addressing in microcontroller-based designs
• Logic function generation
• Analog-to-digital conversion (ADC) systems

The 74HC151N comes in a 16-pin Dual Inline Package (DIP). Below is the pinout and description:

1. Power Supply: Connect the Vcc pin (16) to a positive voltage source (2V to 6V) and the GND pin (8) to ground.
2. Data Inputs: Connect up to 8 data sources to the input pins I0 to I7.
3. Select Lines: Use the select pins A, B, and C to choose which input (I0–I7) is routed to the output. The binary combination of these pins determines the selected input.
   • For example, if A=0, B=1, and C=0, the multiplexer will select I2.
4. Enable Pin: The G pin is an active-low enable input. Ensure this pin is connected to ground (logic LOW) to enable the multiplexer. If this pin is HIGH, the output will be disabled.
5. Output: The selected input signal will appear on the Y pin. The inverted version of the output is available on the W pin.

• Ensure the supply voltage does not exceed the maximum rating of 6V to avoid damaging the component.
• Use pull-up or pull-down resistors on unused input pins to prevent floating inputs, which can cause unpredictable behavior.
• The propagation delay (~16ns at 5V) should be considered in high-speed applications.
• Avoid exceeding the maximum output current of ±25mA to prevent overheating or damage.

Below is an example of how to use the 74HC151N with an Arduino UNO to select and read one of eight input signals.

• Connect Vcc to the Arduino's 5V pin and GND to the Arduino's GND.
• Connect the select pins A, B, and C to Arduino digital pins 2, 3, and 4, respectively.
• Connect the G pin to GND to enable the multiplexer.
• Connect the Y pin to an Arduino analog input pin (e.g., A0).
• Connect your data sources to the input pins I0 to I7.

// Define select pins
const int selectPinA = 2; // Connect to pin A of 74HC151N
const int selectPinB = 3; // Connect to pin B of 74HC151N
const int selectPinC = 4; // Connect to pin C of 74HC151N

// Define multiplexer output pin
const int muxOutputPin = A0; // Connect to pin Y of 74HC151N

void setup() {
  // Set select pins as outputs
  pinMode(selectPinA, OUTPUT);
  pinMode(selectPinB, OUTPUT);
  pinMode(selectPinC, OUTPUT);

  // Initialize serial communication for debugging
  Serial.begin(9600);
}

void loop() {
  for (int i = 0; i < 8; i++) {
    // Set the select pins to the binary representation of i
    digitalWrite(selectPinA, i & 0x01); // LSB
    digitalWrite(selectPinB, (i >> 1) & 0x01);
    digitalWrite(selectPinC, (i >> 2) & 0x01); // MSB

    // Read the selected input
    int value = analogRead(muxOutputPin);

    // Print the value to the serial monitor
    Serial.print("Input ");
    Serial.print(i);
    Serial.print(": ");
    Serial.println(value);

    delay(500); // Wait for 500ms before reading the next input
  }
}

1. No Output Signal on Y Pin

   • Ensure the G pin is connected to ground (logic LOW) to enable the multiplexer.
   • Verify that the select pins (A, B, C) are correctly configured to select the desired input.

2. Unstable or Noisy Output

   • Check for floating input pins. Use pull-up or pull-down resistors on unused inputs.
   • Ensure the power supply is stable and within the specified range (2V to 6V).

3. Component Overheating

   • Verify that the output current does not exceed ±25mA.
   • Check for short circuits or incorrect wiring.

Q: Can the 74HC151N handle analog signals?
A: The 74HC151N is designed for digital signals. While it can pass low-frequency analog signals, it is not optimized for high-precision analog applications.

Q: What happens if the enable pin (G) is HIGH?
A: When the G pin is HIGH, the multiplexer is disabled, and the output pins Y and W will not reflect any input signal.

Q: Can I cascade multiple 74HC151N multiplexers?
A: Yes, you can cascade multiple multiplexers to handle more inputs. For example, two 74HC151N chips can be used to select from 16 inputs.