1-to-2 Demultiplexer

Build a 1-to-2 demultiplexer—route one input signal to one of two outputs based on a selector switch!

Overview

A demultiplexer (DEMUX) is the reverse of a multiplexer—instead of selecting one of many inputs, it routes one input to one of many outputs. The 1-to-2 DEMUX is the simplest form: one data input, one selector, and two outputs. When the selector is 0, the input appears at output Y0; when the selector is 1, the input appears at output Y1. This is the building block for address decoders, data distribution, and memory chip selection.

Components Needed

  • 1x SN74HC04 IC (Hex Inverter)
  • 1x SN74LS08 IC (Quad AND)
  • 2x Switch
  • 2x LED
  • severalx Wires

Instructions

  1. Gather Your Components

    Collect the SN74HC04 (NOT) and SN74LS08 (AND) ICs, two switches (one for data input, one for selector), two LEDs (for the two outputs), wires, breadboard, and 5V power supply.

  2. Wire the DEMUX Circuit

    Place both ICs on the breadboard and connect power. Wire the selector switch (S) to a NOT gate. Feed the data input (D) and NOT(S) into one AND gate for output Y0. Feed D and S into another AND gate for output Y1. Connect each AND output to an LED.

  3. Test: Selector=0, Input=0 → Output 00

    Selector is 0 (routing to Y0), but input D is also 0. No data to route, so both outputs are OFF. Output: 00.

  4. Test: Selector=1, Input=0 → Output 00

    Selector is 1 (routing to Y1), but input D is still 0. Both outputs remain OFF. Output: 00.

  5. Test: Selector=0, Input=1 → Output 10

    Selector is 0 and input D is 1. The data is routed to Y0! The left LED (Y0) turns ON while Y1 stays OFF. Output: 10.

  6. Test: Selector=1, Input=1 → Output 01

    Selector is 1 and input D is 1. The data is routed to Y1 instead! The right LED (Y1) turns ON while Y0 stays OFF. Output: 01. The DEMUX correctly steers the input to the selected output!

Challenges

  • Extend to a 1-to-4 DEMUX by adding a second selector and more AND gates
  • Build a complete MUX-DEMUX pair and route a signal through both
  • Use the DEMUX to selectively enable one of two circuits
  • Think about how this relates to memory chip select signals