How to Craft a Redstone Comparator
- Make smooth stone. Smelt cobblestone into stone, then smelt stone again to get smooth stone. You need 3.
- Gather quartz. Mine nether quartz in the Nether, or obtain it via trading or other methods available in your game version.
- Craft redstone torches. You need 3 total.
- Use the crafting table layout. Place 3 smooth stone across the bottom row. Place 1 nether quartz in the center. Place 3 redstone torches in a V shape around the quartz: one above it (top middle) and one on each side (middle left and middle right).
How to Place It
- Face the output forward. The comparator outputs from the end with the single front torch.
- Feed the main input from the back. The end with two small rear torches is the main input.
- Side inputs go on the left and right. These are the “comparison” or “subtraction” inputs.
Two Modes
Think of a comparator as an analog logic gate plus an inventory sensor. Same cozy footprint as a repeater, very different job.
Compare mode (front torch off)
The comparator outputs the rear signal strength if it is greater than or equal to the strongest side signal. If the side signal is stronger, output becomes 0.
Subtract mode (front torch on)
The comparator outputs: max(rear input minus strongest side input, 0). If the result would be negative, it outputs 0.
Reading a Container
- Place the comparator directly behind the container. The comparator’s rear input should touch the block you are reading.
- Run redstone dust from the output. This carries the strength value (0 to 15).
- Test it with a lamp. A redstone lamp is a nice “yes, we have output” check.
3 Builds You Will Use
1) Simple “full enough” light
- Put a comparator behind a chest.
- Run dust into a redstone lamp.
- Add items until the lamp turns on at the fullness you care about. If you want a cleaner threshold, pair this with a second comparator in subtract mode to “trim” the output to your target.
2) Item filter backbone (classic hopper filter)
This is the part where I say: filters are picky, but they are worth it.
- Core parts: hopper, comparator, redstone dust, repeater, redstone torch, and a place to store the filtered items.
- Classic setup note: Many builds use a “filter” hopper stocked with a pattern like 41 of the target item plus 1/1/1/1 filler items in the other slots. That keeps the signal stable so it only triggers for the right item.
Tip: Build carefully, then test with a single item first before dumping your whole storage into it.
3) Smelter inventory indicator
A comparator on a furnace does not magically know when your steak is “done.” What it actually reads is the furnace’s inventory fullness (input, fuel, and output together). That is still useful.
- Put a comparator behind a furnace (or smoker or blast furnace).
- Use the output to power a lamp as a rough “something is in here” or “output is filling up” indicator.
- If you want a more true “ready” vibe, design around what you care about: for example, let the output slot fill up and use that rising fullness to trigger your lamp or a collection pulse.
Troubleshooting
- Random behavior? Check for accidental side inputs. A single dust line next to the comparator can change the whole decision.
- Weak output? Dust loses strength over distance. Use repeaters to refresh signals, and comparators when you need to preserve or compute strengths.
- Reading the wrong block? Make sure the comparator is touching the block you want to read from the rear side, not the output side.
