Redstone comparators in Minecraft are incredibly versatile components for automation, especially when it comes to monitoring inventories and processes. One common application is using comparators with furnaces to detect when smelting is complete or to manage fuel levels. However, the way a redstone comparator interacts with a furnace isn’t always intuitive, and the signal strength it outputs can seem somewhat random at first glance. Let’s break down the mechanics behind the redstone comparator when used with furnaces in Minecraft, and understand the nuances of its behavior.
Understanding Comparator Basics in Minecraft
Before diving into the specifics of furnaces, it’s crucial to understand what a redstone comparator fundamentally does. In Minecraft, a comparator performs several key functions related to redstone signals:
- Comparison: It can compare the signal strength of two incoming redstone signals.
- Subtraction: It can subtract the signal strength of a side input from the main back input.
- Measurement: Most relevantly for furnaces, it can measure the signal strength of containers, including furnaces, based on their filled slots.
When a comparator is placed next to a furnace, it enters measurement mode. In this mode, it outputs a redstone signal strength proportional to the number of filled slots in the furnace. However, the calculation isn’t simply based on the number of stacks, but rather the number of items within those slots, up to a stack size of 64 for most items. This is where the complexity starts to emerge when considering smelting.
Furnace Output and Signal Strength: The Item Count
The signal strength a comparator reads from a furnace is based on the total number of items within the furnace’s input and fuel slots. A full furnace, meaning all slots filled to their maximum stack size (64 for most items), will output the maximum signal strength of 15. A completely empty furnace will output no signal (strength 0). The signal strength scales linearly between these points, but not in a perfectly straightforward way due to how Minecraft calculates these signals in ranges.
Let’s consider a simplified example. If you place a single item in a furnace, whether it’s a piece of ore or a piece of coal, the comparator will output a signal strength. As you add more items, the signal strength will increase, but not with each individual item. Instead, the signal strength increases in steps, based on ranges of item counts.
The Quirks of Coal and Smelting Calculation
The original observation highlights a crucial point: when smelting, the total number of items in the furnace changes as fuel is consumed and ore is converted into ingots. This dynamic item count affects the comparator signal in ways that can be initially confusing.
Imagine you start with 64 coal and 64 iron ore in a furnace. Initially, you have 128 items in total (64 coal + 64 ore). This high item count will result in a relatively strong comparator signal. As the coal burns and smelts the iron ore into iron ingots, the total number of items in the furnace decreases. For every piece of coal consumed, one iron ore is transformed into one iron ingot, effectively reducing the total item count in the furnace as the smelting process progresses.
This decrease in the total item count is what causes the comparator signal to weaken over time during the smelting process. The original post notes that starting with 64 coal and 64 iron ore results in an initial high signal, but as smelting progresses, the signal strength drops. This is because the total items are reducing from 128 downwards.
Incomplete Smelt Detection Problem
The most significant challenge identified is that using a comparator directly to detect the completion of a full smelt is unreliable. The signal strength drops as the coal is consumed, but this drop doesn’t precisely coincide with the moment all ore is smelted.
As the original post describes, the signal strength might drop when you still have a mix of unsmelted ore, ingots, and remaining coal in the furnace. Furthermore, if you were to remove the ingots and add more ore while leaving the remaining coal, the signal strength behavior becomes even less predictable for detecting a full smelting cycle.
The issue arises because the comparator is measuring the total item count, not the ratio of smelted to unsmelted items, or the remaining fuel. Therefore, a simple comparator setup directly on the furnace isn’t ideal for precisely indicating when all ore has been converted into ingots.
Single Item vs. Smelting Item Signal Strength Ranges
To further illustrate the behavior, let’s look at the signal strength ranges observed for single item types and during smelting, as provided in the original analysis:
For single items (coal or ore):
- 1 – 13 items: 1 redstone dust signal
- 14 – 27 items: 2 redstone dust signal
- 28 – 41 items: 3 redstone dust signal
- 42 – 54 items: 4 redstone dust signal
- 55 – 64 items: 5 redstone dust signal
For smelting (64 Ore with varying Coal amounts, resulting total items in furnace in parentheses):
- 64 Ore / 1 – 4 Coal (68 Items): 5 redstone dust signal
- 64 Ore / 5 – 18 Coal (82 Items): 6 redstone dust signal
- 64 Ore / 19 – 31 Coal (95 Items): 7 redstone dust signal
- 64 Ore / 32 – 45 Coal (109 Items): 8 redstone dust signal
- 64 Ore / 46 – 59 Coal (123 Items): 9 redstone dust signal
- 64 Ore / 60 – 64 Coal (128 Items): 10 redstone dust signal
These ranges demonstrate the stepped nature of the comparator output and how the total number of items influences the signal strength. Notice how adding more coal to a fixed amount of ore increases the signal strength because the total item count goes up.
Practical Implications for Redstone Automation
While using a comparator directly on a furnace to detect full smelting completion is flawed, comparators are still incredibly useful in furnace-based automation. Instead of focusing on completion detection with a single comparator, you can use comparators for other valuable functions, such as:
- Fuel Level Monitoring: You can use a comparator to detect when the fuel level in a furnace drops below a certain threshold, triggering a refuel mechanism. This is more reliable because you are monitoring fuel consumption, a more consistent metric.
- Approximate Smelting Progress Indication: While not precise for completion, the comparator signal can still give a general indication of smelting progress based on the decreasing item count. This could be useful for visual displays or less critical automation steps.
To achieve more precise smelting completion detection, you would typically need to employ more complex redstone circuits, possibly involving item filters, timers, or combinations of multiple comparators to analyze different aspects of the furnace’s state or the item flow in your system.
Conclusion: Understanding the Nuances
In conclusion, while the redstone comparator is a powerful tool for interacting with furnaces in Minecraft, understanding what it measures – the total item count – is crucial to using it effectively. Directly detecting full smelting completion based solely on a comparator reading the furnace is unreliable due to the changing item counts during the smelting process. However, for fuel monitoring and general progress indication, comparators remain valuable. By understanding these nuances, you can design more robust and predictable redstone automation systems for your Minecraft worlds.
