Introduction

The 74LS151 is an 8-to-1 multiplexer IC, meaning it can take eight input signals and output one of them based on the binary value of its select lines. Multiplexers are useful for routing multiple signals to a single output, saving on wiring or logic resources in digital systems.

Materials Required

• 74LS151 Multiplexer IC
• 8 input switches
• LED to display the output
• 3 binary input select switches
• Breadboard and connecting wires
• Power supply (5V)

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Circuit Diagram

Below is the circuit diagram for the 74LS151 multiplexer experiment:

Pin Configuration

The 74LS151 IC has 16 pins. Below is the pin configuration:

• Inputs: I0 to I7 (eight data inputs)
• Select Lines: A, B, C (three select inputs)
• Output: Y (multiplexed output)
• Enable Input: G (active LOW enable input)

Steps for the Experiment

1. Place the 74LS151 IC on the breadboard.
2. Connect eight input switches to the input pins (I0 to I7) of the IC.
3. Connect the select input switches (A, B, C) to the select pins (pins 11, 10, 9) to choose which input is directed to the output.
4. Connect an LED to the output pin (Y) to display the selected input.
5. Set the enable input (G) to logic LOW (GND) to activate the multiplexer.
6. Connect the power supply (5V) to the VCC pin and ground to the GND pin.
7. Power the circuit and toggle the select inputs to see how different input lines are multiplexed to the output.

Explanation

The 74LS151 multiplexer takes eight input signals (I0 to I7) and directs one of them to the output (Y) based on the binary value of the select inputs (A, B, C). For example:

• If the select input is 000, the output will be the value of I0.
• If the select input is 001, the output will be the value of I1.
• This continues up to the select input 111, which will output the value of I7.

The enable input (G) is active LOW, meaning the multiplexer only functions when this pin is connected to ground.

Results and Observations

As you change the select inputs (A, B, C), the output (Y) will change according to the state of the selected input (I0 to I7). The output LED should display the value of the currently selected input. For instance:

• Select 000: The LED will show the value of I0 (on or off).
• Select 101: The LED will show the value of I5.

Applications of the 74LS151

Multiplexers like the 74LS151 are widely used in digital systems to reduce the number of data lines needed. They are used in data routing, digital communication, and even in complex decision-making circuits where multiple inputs need to be evaluated and routed to a single output.

Conclusion

In this experiment, we explored the operation of the 74LS151 multiplexer and demonstrated how it can route one of eight inputs to a single output based on the select input values. Multiplexers are critical in digital systems, helping to simplify circuit designs and efficiently route data.