40d:Fluid logic

Fluid logic is a form of computing which uses a fluid (generally water) controlled by various means, to trigger pressure plates and hopefully accomplish some desirable result.

Infinite Flow Gates

These logic gates are relatively simple and cheap to make, but require an infinite amount of water and infinite drainage to operate. You can build a circuit system to prevent the loss of water, but closing constructions like floodgates will always destroy water, so you'll always have replace it somehow. The following examples use raising bridges and floodgates, as they have the same delay of 100 steps when reacting to on/off signals. The bridges work as inverted input as they block passage when recieving an on signal while floodgates open in that case.

(N)AND

█ █ █ █ █ ≈ X A X B ^ · █ █ █ █ █

An AND gate is simply created by putting two floodgates in a row, each one connected to one of the input triggers. When both floodgates recieve an on signal, they will open and let the water from the left side pass. The pressure plate behind the floodgates has to be constructed to react on 4-7 water. If you use a pressure plate reacting on 0-3 water, you'll get a NAND gate instead. It's also possible to add more floodgates to process more than two signals in a conjunction, and to use two oppositional pressure plates to get the result of the AND and NAND operation at the same time. If you use a single floodgate and a 0-3 pressure plate, you'll get a NOT gate.

(N)OR

█ █ █ █ █ ≈ ╬ A ╬ B ^ · █ █ █ █ █

An OR gate is simply created by putting two 1x1 raising bridges in a row, each one connected to one of the input triggers. When one of the bridges recieves an on signal, it will raise and blocks the water passage from the left side. The pressure plate behind the bridges has to be constructed to react on 0-3 water. If you use a pressure plate reacting on 4-7 water, you'll get a NOR gate instead. It's also possible to add more floodgates to process more than two signals in a disjunction, and to use two oppositional pressure plates to get the result of the OR and NOR operation at the same time. If you use a single bridge and a 4-7 pressure plate, you'll get a NOT gate.

(N)XOR/EQUAL

█ █ █ █ █ ≈ X A ╬ B █ █ ≈ █ █ ^ · ≈ X B ╬ A █ █ █ █ █ █ █

A XOR gate is created by putting 1x1 raising bridges and floodgates together. Bridge and floodgate A are linked to the same input and bridge and floodgate B are both linked to the other input. When one of the inputs sends an on signal, the bridge will raise/close and the appropriate door will be opened. Only when the floodgate and the bridge at one passage are open, what happenes when exactly one input singal is on, the water will flow to the right. The pressure plate behind the bridges has to be constructed to react on 4-7 water. If you use a pressure plate reacting on 0-3 water, you'll get a NXOR/EQUAL gate instead. It's also possible to use two oppositional pressure plates to get the result of the XOR and NXOR operation at the same time. Processing more input signals is possible but requires an exponentially growing amount of bridges, floodgates and therefore mechanism. It is easier to link the output to another XOR gate.

As mentioned, you can just add more floodgates and bridges and even pressure plates to expand your gates to process more input signals. You can combine floodgates and bridges as you need them. The XOR gate for example is nothing else than combined logic: A XOR B = (A AND NOT B) OR (NOT A AND B). But sometimes it is easier to use more but simpler gates.

CMOS Transmission Gate and Inverter Logic

Perhaps the closest to utilizing water as a stand-in for electricity, transmission gate logic can be accomplished by simply having an infinite water source in place of all +Vs, and infinite drainage for all grounds. Simple floodgates behave as standard transmission gates, while bridges are inverted gates. However, unlike the other forms of fluid logic, but like a real world electrical circuit, a dedicated inverter is required, which must be hooked up to +V and ground.

Advanced CMOS Gates

This type of logic uses the same concept as real CMOS circuits do, which causes them to minimalize power (in this case, water) consumption. The idea is that water should only flow when there is a state change.

Basic Design

Let's say we want to evaluate the logical expression f. It can be a simple and or or gate, or anything more complicated. Follow the following scheme:

≈	≈	≈
╗	A	╔
║	^	║
║	B	║
║	#	║

Here, A is a set of floodgates and/or drawbridges that let water flow exactly when f evaluates to true, B is the same except that it lets water flow when f evaluates to false, ^ is a pressure plate set to activate on water levels 4-7, and # is the drain.

Examples

In the following examples, X is a floodgate, and ╬ is a drawbridge. Red ones are connected to input A, green ones to input B and blue ones to input C.

NOT

≈	≈	≈
╗	╬	╔
║	^	║
║	X	║
║	#	║

AND

≈	≈	≈	≈
╗	X	╔	═
║	X	║	█
║	^	╚	╗
║	█	█	║
║	╬	╬	║
║	#	#	║

OR

≈	≈	≈	≈
╗	X	X	╔
║	█	█	║
║	^	╔	╝
║	╬	║	█
║	╬	║	█
║	#	║	█

XOR

This is not as straightforward as the previous ones. The true expression is the following: (A and not B) or (not A and B). The false expression: (A and B) or (not A and not B).

So the gates look like the following:

≈	≈	≈	≈	≈
╗	X	║	X	╔
║	╬	║	╬	║
║	█	^	█	║
║	╬	║	X	║
║	╬	║	X	║
║	#	║	#	║

Advantages And Disadvantages

The basic advantage of this design is that it uses much less water than infinite flow gates. A river is enough to supply even the more complex systems, maybe with an added reservoir to neutralise flow irregularities. Similarly, for the drain, it is enough to excavate a cavern where the water can evaporate.

The disadvantage is that it requires much more resources and time to construct, especially more mechanisms. And more planning, since floodgates tend to block paths when constructed.

Faster Version

The main factors that affect the speed of these gates are the delays of floodgates and bridges, and the switch-off delay of pressure plates. These cannot be eliminated.

Another factor is the flowing speed of the water. It can be improved. First, the water should flow in from a reservoir a few z-levels higher then the gates themselves (the more the better). This way, water will flow in much faster. Next, replace the pressure plates with up stairs, and make a 2x1 room one z-level above. On on tile is a down stair, and on the other is the pressure plate. Now the water will also flow out faster, or at least the pressure plate will switch off sooner.

This increases the water consumption a bit, but it still remains relatively low.