A repeater sitting in a dust line. Refreshes the signal so it can travel further. Footprint 1 wide × 4 deep × 2 tall. Build it block by block in Minecraft.
How to build it
The photo reads bottom-to-top:
Place a lever at the bottom as input A.
Run redstone dust up to a solid block.
Set a redstone repeater on top of that block, pointing toward
the output. You'll see it as a short flat tile with a small torch
mark on its side.
Put another solid block on top of the repeater output so the
signal continues upward.
Run dust across the top of that block to the output consumer —
a note block in the photo.
Why it works
A repeater acts as a one-way valve and a signal amplifier:
It reads any non-zero input and re-emits the signal at full
strength (15), no matter how weak the input was.
Pointing direction matters. Place the repeater so the end with
the little torch receives power, and the flat end emits power.
Because redstone dust loses one level per block and dies after 15,
anything longer than ~10 blocks benefits from a repeater somewhere
along the way. "Buffer" is the digital-logic name for this refresh
role.
Gotchas
Repeaters introduce a 1-tick delay by default. Right-click to
cycle through 1, 2, 3, or 4 ticks. Useful as a tunable delay when
you're synchronizing signals.
Over short distances you don't need a buffer at all — dust just
works. Reach for this pattern when a signal is fading out over a
long run or when you want to add a small deliberate delay.