Getting Started with Redstone ② Repeater and Comparator — Extending, Delaying, and Locking Signals

In episode 1, we saw that redstone dust loses its signal after 15 blocks. So how do we open a door that’s 30 blocks away? And how can we make it light up only when the chest is full? The answer lies in the two components of this episode: redstone repeater and redstone comparator.

Both are flat like half blocks and have a small torch on top, which can be confusing at first. The way to tell them apart is simple: if there are two torches side by side, it’s a repeater; if there are three in a triangular shape, it’s a comparator.

Four functions of the repeater

① Resetting the signal to 15

The repeater outputs a signal strength of 15 regardless of the incoming signal strength. Even if there’s only 1 left, it will reset to 15 after passing through the repeater. You can extend long circuits by placing a repeater every 15 blocks.

② One-way transmission

The repeater receives signals from behind and only sends them forward. Signals cannot pass in the opposite direction. This makes it useful as a 'one-way sign' to prevent two circuits from mixing. The direction you place it in determines where the signal goes, so pay attention to the arrow shape when placing it.

③ Delaying signals

Right-clicking the repeater will move the front torch and change the delay time to 1-4 ticks. One tick is 0.1 seconds. By chaining multiple repeaters, you can create time delay devices like "the door opens 1 second after pressing the button."

④ Locking signals

When an active repeater (or comparator) faces the side of another repeater, the repeater that gets hit will lock in its current state. Even if the signal changes from behind, the output signal remains unchanged. A gray bar appears above the locked repeater, making it visible. This is the basis for devices that 'remember' states.

Comparator — The component that 'measures' signals

While the repeater boosts signals, the comparator compares and measures signals. It may seem complicated at first, but once you understand its uses, redstone becomes much smarter.

Two modes

The comparator compares the signal coming from behind with the signal coming from the side. Right-click the front small torch to switch modes.

Modes	Front torch	Output signal
Comparison mode	Off	If the back signal is greater than or equal to the side signal, it outputs the back signal as is, otherwise it outputs 0.
Subtraction mode	On	Back signal − side signal (if it’s less than 0, it outputs 0).

If there’s nothing next to it, both modes will output the back signal as is. Unlike the repeater, remember that it does not boost signals to 15.

Real power — Reading the 'state' of blocks

The greatest use of the comparator is not comparing signals. When a specific block is placed behind the comparator, it reads the state of that block and converts it to a signal strength of 0-15.

• Chests, barrels, hoppers, and furnaces — how full they are. If empty, it’s 0; if full, it’s 15.
• Cake — number of remaining slices.
• Composters and cauldrons — height of fill.
• Item frames — how many times the item inside has been rotated.
• Jukeboxes — which record is inside.

Why is this important? It allows you to create devices that can make decisions based on situations, like "notify me when the chest is full" or "take out items when the furnace is done cooking." This function is key to automatic farms' 'storage is full' lamps and item sorters.

Summary of Episode 2

	Repeater	Comparator
Appearance	Two torches	Three torches (triangle shape)
Signal strength	Always set to 15	Not increased
Main uses	Increase, delay, direct, toggle	Compare, subtract, read block state

Now that you know how to create (Episode 1) and increase and measure (Episode 2) signals, in the final Episode 3, we'll use this signal to move blocks. We'll create the first piston door that opens and closes with pistons, sticky pistons, and a lever.