Minecraft comparators are incredibly useful redstone components, especially when it comes to automation. One common application is monitoring furnaces, but the way comparators interact with furnaces and fuel levels can be a bit confusing. This guide will break down the mechanics of using comparators with furnaces in Minecraft, focusing on how signal strength is affected by fuel and smelting processes.
How Comparators Read Furnace Levels
Minecraft comparators, when placed next to a furnace, read the fill level of the furnace’s inventory slots. This includes both the fuel slot and the ingredient slot. The comparator outputs a redstone signal strength based on the total number of items in these slots, ranging from 0 to 15. A full furnace, containing a stack of 64 items in any slot combination that sums to 64 or more across both slots, will produce a maximum signal strength of 15.
However, the signal strength isn’t directly tied to the progress of smelting or the amount of smelted items. This is a crucial point to understand. The comparator simply reads the quantity of items present in the furnace at any given time, regardless of whether they are raw materials, fuel, or finished products.
The Peculiar Nature of Fuel and Smelting Signals
Let’s consider a common scenario: smelting iron ore with coal. If you place 64 iron ore and 64 coal in a furnace, you start with a total of 128 items. Initially, a comparator connected to this furnace will output a strong signal. As the coal burns and smelts the iron ore, the total number of items in the furnace decreases because coal is consumed.
Here’s where things get interesting. As the smelting process begins, the total item count in the furnace drops. For example, smelting 64 iron ore with 64 coal will eventually reduce the total items. If you start with 128 items (64 coal + 64 ore), and 8 coal are consumed to smelt 64 items, the total items reduce to 120 (56 coal + 64 ore/ingot during the process). This change in total items leads to a change in the comparator signal strength.
The original observation noted that starting with 64 coal and 64 iron ore yields a comparator output of 1 redstone dust and 10 redstone strength. This highlights that the signal strength is not solely determined by the type of item but primarily by the total count. Crucially, the signal strength from smelted items (like iron ingots) does not inherently change compared to the raw ore.
Challenges in Detecting Full Smelt Completion
This behavior leads to some interesting challenges when trying to use comparators to precisely detect when a furnace has finished smelting a batch of items.
One issue is that the signal strength can drop before the entire smelting process is complete. For instance, if you are smelting 64 iron ore with 64 coal, the signal strength will decrease as coal is consumed. However, this drop doesn’t necessarily indicate that all 64 iron ore have been smelted. The signal might drop when you still have a mix of unsmelted ore, ingots, and remaining coal in the furnace. This makes it difficult to reliably detect the exact moment when smelting is 100% finished based solely on the comparator signal drop.
Another complication arises when you try to refill the furnace. If you remove the smelted ingots and add more ore while leaving the remaining coal, the signal strength might not behave as expected for detecting the completion of the next smelting cycle. The signal drop might be delayed because of the leftover fuel, making it inconsistent for automation that relies on precise full-smelt detection.
Decoding Signal Strength: Item Stacks and Smelting Ranges
To further illustrate the signal behavior, let’s look at the signal strength ranges based on item counts, both for general item stacks and specifically in smelting scenarios (without considering the comparator itself, but the redstone dust signal strength equivalent).
For single item stacks (coal or ore alone in a container):
- 1 – 13 items: 1 redstone dust strength
- 14 – 27 items: 2 redstone dust strength
- 28 – 41 items: 3 redstone dust strength
- 42 – 54 items: 4 redstone dust strength
- 55 – 64 items: 5 redstone dust strength
For smelting 64 Ore with varying amounts of Coal (showing total items and equivalent redstone dust strength):
- 64 Ore / 1 – 4 Coal (68 Total Items): 5 redstone dust strength
- 64 Ore / 5 – 18 Coal (82 Total Items): 6 redstone dust strength
- 64 Ore / 19 – 31 Coal (95 Total Items): 7 redstone dust strength
- 64 Ore / 32 – 45 Coal (109 Total Items): 8 redstone dust strength
- 64 Ore / 46 – 59 Coal (123 Total Items): 9 redstone dust strength
- 64 Ore / 60 – 64 Coal (128 Total Items): 10 redstone dust strength
These ranges demonstrate how the total number of items in the furnace directly influences the signal strength. When automating with comparators and furnaces, it’s essential to consider these nuances and design your redstone circuits accordingly. While comparators are useful for detecting changes in furnace item levels, precise full-smelt detection requires more sophisticated logic than simply monitoring the comparator signal drop. Understanding these mechanics is key to effective furnace automation in Minecraft.
