EDGE DETECTOR

When to Use

One-shot triggers from levers, detecting the exact moment a signal changes, preventing repeated activations.

Materials

• ▸1 Redstone Repeater
• ▸Redstone Dust
• ▸1 Redstone Comparator or Torch

Overview: what the Edge Detector is and does

Converts a sustained signal into a brief pulse at the moment the signal turns on (rising edge) or off (falling edge). Essential for triggering actions exactly once per state change.

As a pulse circuit it reshapes the length or edges of a signal rather than generating one, which is how redstoners tame button presses and observer flashes.

In practice it is used for one-shot triggers from levers, detecting the exact moment a signal changes, preventing repeated activations. The build below targets vanilla Java Edition 1.21.

How it works: the redstone mechanics

It works by racing a signal against a slightly delayed copy of itself: a comparator (or torch) passes power only during the brief window before the delayed path catches up, producing a pulse roughly as long as the repeater delay you set.

It is assembled from 1 Redstone Repeater, redstone Dust, and 1 Redstone Comparator or Torch, and each of those parts plays a specific timing or logic role in the circuit rather than being interchangeable filler.

Because this is a pulse-shaping circuit, the thing to watch as you build is the relative timing of the two signal paths, since the output window is the gap between them.

How to build it

1. 1Rising edge: Split the input into two paths.
2. 2Delay one path with a repeater (1+ ticks).
3. 3Feed the delayed path as the side input of a comparator reading the direct path.
4. 4The comparator outputs only during the brief moment before the delayed signal arrives.
5. 5Falling edge: Invert the input first with a NOT gate, then apply the same technique.
6. 6Power it up and watch one full cycle: confirm it produces a pulse of the length you intended before wiring it into a larger contraption.

Uses & applications

• ▸One-shot triggers from levers, detecting the exact moment a signal changes, preventing repeated activations.
• ▸Repeater-comparator edge detector (most common) — a variant suited to particular space or timing needs.
• ▸Observer-based (observer IS a rising-edge detector) — a variant suited to particular space or timing needs.
• ▸Piston-based edge detector (piston breaks dust momentarily) — a variant suited to particular space or timing needs.
• ▸Dual-edge detector (pulses on both rising and falling edges) — a variant suited to particular space or timing needs.

Tips & common mistakes

• !Set the repeater delay too low and the output pulse is a single tick that fast pistons may miss — give it 2 ticks if a downstream piston must react.
• !Test the output pulse length with a redstone lamp before committing — the lamp's own 2-tick off delay aside, you will see at a glance whether the timing is right.
• !Remember that bare redstone dust loses 1 signal strength per block, so insert a repeater before any run exceeds 15 blocks inside this circuit.

Edge Detector FAQ