1-to-2 demultiplexer

One signal in, two possible exits — a selector picks which one receives it. A ready-made routing circuit you can open in the TorchAnvil simulator.

The mux, run backwards

A multiplexer funnels many inputs down to one. A demultiplexer does the opposite — it takes one input and a selector, and forwards the signal to exactly one of several outputs. This is the 1-to-2 version: one input, one selector bit, two exits.

How it works

Two AND gates, each guarding one exit:

• Out 0 = In AND NOT Sel. This lamp lights when Sel is off.
• Out 1 = In AND Sel. This lamp lights when Sel is on.

Because the two AND gates share the In signal but gate it with opposite Sel conditions, at most one lamp can ever be on. When In = 0, both stay dark — you can't route silence anywhere meaningful.

In	Sel	Out 0	Out 1
0	0	0	0
0	1	0	0
1	0	1	0
1	1	0	1

Why it matters

Pair a mux with a demux and you have a one-wire bus: the mux on the sending side picks whose turn it is to talk, the demux on the receiving side delivers the signal to the right listener. Same pattern drives memory write-enables, interrupt dispatch, and the address decoder on the next sample over.

Try this

• Turn In on, then flip Sel back and forth. The "lit" lamp migrates between Out 0 and Out 1 — the signal itself is getting routed.
• Turn Sel on but leave In off. Nothing lights. A demux needs something to forward; it won't invent signal out of thin air.