How to Make a Redstone Clock

Guide Java Bedrock

Quick answer: The easiest redstone clock is a repeater loop: 2 or more repeaters wired in a circle with a lever to start it, pulsing forever. For longer periods use a hopper clock - two hoppers passing items between them with comparators reading them - or an observer clock that pulses twice per second. Clocks power farms, doors and light shows.

What you need

Repeaters / 2 observers / 2 hoppers + comparator
Redstone dust
Lever (on/off switch)
Items for the hopper clock

Step by step

Build a repeater clock (fast). Place 2 repeaters in a loop facing each other with dust between them, pulse it with a lever flick, and it cycles forever. Add more repeaters (up to 0.4s delay each) to slow the pulse.
Build an observer clock (simplest). Face two observers into each other - each watches the other change and fires back, creating a compact 2-pulses-per-second clock with zero wiring.
Build a hopper clock (slow and precise). Place 2 hoppers facing into each other, put 1-64 items inside, and read one with a comparator. The items shuttle back and forth at 2.5 items per second; one item gives about a 0.8-second cycle, a full stack about 51 seconds.
Kill the flicker. Torch clocks (a torch with dust looping back into its own block) pulse fast but burn out and restart randomly - use repeaters or observers instead for anything important.
Hook it to your machine. Run the clock output into pistons (item elevators), dispensers (auto-farms), droppers, or note blocks. Add a lever in the line to switch the whole machine on and off.

Java vs Bedrock

Repeater and hopper clocks behave the same in Java and Bedrock. Observer clocks differ slightly in timing between editions, and comparator repeater-lock tricks are Java-only. Burned-out torch clocks recover on their own in both.

Versions: Hopper clocks became possible when hoppers and comparators arrived in 1.5 (the Redstone Update, 2013), and observer clocks arrived with observers in 1.11. The repeater loop is the oldest clock design, from Beta 1.3.

Frequently asked questions

Which clock should I use?

Observer pair for fast pulsing (farms, dispensers), hopper clock for slow cycles (mob farm flushing, item sorters), repeater loop for anything in between with fine delay control.

Why did my repeater clock stop?

If the loop ever loses its pulse (chunk unload, lever timing), it stays dead. Build in a starter: a lever or button that re-injects a pulse, or use a self-starting design with a torch.

Do clocks cause lag?

Fast clocks with many pistons or hoppers can. Use the slowest clock that does the job, and turn machines off with a lever when you're not using them.