# Logic Flows, Literally, In This Water Adder

A lot of elementary electronic texts use water as an analogy for electricity. You know, pressure is voltage, flow is current, and pipe diameter is resistance. It is ironic, then, that some people use fluids to build logic gates and, in fact, you can make any logic circuit you like using nothing but water flowing through some structures. Don’t think so? Have a look at the video from [Steve Mould] below.

Fluidic logic isn’t anything new, but it has always been a bit exotic. Usually, replacing electrons with water or even air — which is a kind of fluid — means you are trying to operate in a tough environment or have some other special need. As far as we can tell, [Steve] did it just because he could, and we get that.

Historically, fluidic logic uses small pressure jets to redirect fluid flows, something the U.S. Army figured out in 1957. However, [Steve’s] take uses some cells that depend on water level and siphon action to work. He also had some impractical logic gates that were very illustrative, even if they didn’t work very well.

The first attempt fell somewhat short, but all problems were eventually resolved. Of course, adding two four-bit numbers is a far cry from a full computer, but you have to admit, it is a start. Old computers used acoustic waves in mercury for memory, so it would be an interesting pairing to build something with the complexity of, say, an EDSAC using this type of construction.

Turns out if you start looking, lots of things can form logic gates, even dominos. You have to wonder if the ancient Egyptians had the idea if they could have made a fluidic computer out of brick and powered it with the Nile? Probably no harder than the pyramids, and you can only wonder what they would have done with it.

## 31 thoughts on “Logic Flows, Literally, In This Water Adder”

1. Phillip says:

I see what you did there! Nice!

1. I see that you saw what she did there. Double nice!

1. Jan says:

“water or even air — which is a kind of fluid”

ehhmmm… no it isn’t, by definition it isn’t, according to many properties it isn’t.
Imagine an adder… with a mterial that is allowed to compress. 1+1 = 1.8 not really good is it?

It’s the same as saying that steel is the same as pottery as they both have the same result when someone drops it on your head from a great height.

Now regarding the project… nice… very nice… thanks for posting!

1. Tom G says:

Sorry, but you are completely wrong. Search for “fluidic logic” and you will see logic gates that are based on gasses at 2-4kPSI.

I once recommended against replacing a fliudic logic FSM with a electronics, because electronics in flammable gas atmospheres is rather dangerous! That was and is on unmanned off-shore oil platforms, but perhaps it will be important in nuclear decommissioning due to its radiation tolerance.

1. And here I thought there were four states of matter: Solid, liquid, gaseous and plasma.
So liquid and gaseous is the same? Just three states of matter?
What about the distinct transitions between liquid and gas like boiling, evaporation and condensing?
—————-
Disregard that. Decided to search for distinction between fluid and liquid and (re-)learned that they are not the same: https://sciencing.com/difference-between-fluid-liquid-5752203.html

But you or @https://hackaday.io/hexagon5un could have pointed that out to Jan instead of just saying “no”.

Wait, does this mean glass is a solid liquid?

1. Dissy says:

“And here I thought there were four states of matter: Solid, liquid, gaseous and plasma.”
That is correct. Also correct is the fact “fluid” is not in your list.
Fluid is a property of a state of matter, not a state in and of itself.

“So liquid and gaseous is the same?”
In that each has a measure of resistance to shear force? Yes.
They both have that property. Plasmas too.
It’s the measure of that resistance that changes depending on the state.

2. Eric Weatherby says:

Glass is an amorphous–that is, non-crystalline–solid at room temperature.

1. Old Guy says:

And over time it does run to the bottom. See 18th century windows.

2. Onetruegod says:

Old Guy is wrong. Glass is solid, the 18th century glass making technique produced panes with varying thickness. The installers would put the thick side down the bottom.

3. Hirudinea says:

Hey, how ’bout some love for Bose–Einstein condensate, its cool!

2. arifyn says:

by definition air *is* a fluid. both liquids and gases are fluids. so are plasmas. anything that can flow is a fluid.

the confusion is understandable because colloquially, people mostly talk about liquid fluids. They’re the ones we can actually see.

1. Troepje says:

Ohhh never knew the difference between liquid and fluid, but in my defence, English is not my first language, in Dutch that difference doesnt exist afaik.

1. Thrasher says:

Then it would absurdly follow that there are no Dutch physicists.
I don’t know Dutch but liquid-fluid vloeibare-vloeistof.

2. required says:

Go 3 miles deep into easy crust and solid is a fluid.

3. Jan says:

Thanks for your replies/info, I learned something new today. What a great day.

2. I guess this is the first true ripple carry adder?
(I’m sorry. I’ll leave.)

3. RÖB says:

Now … with a constant current flow source he should be able to make a 555

1. Phillip says:

But can it run Doom?

1. mt21 says:

No but you can play Ecco the Dolphin with it

4. JJ says:

Do it with light…. and you have a supercomputer :-)

5. Dan says:

My granny had a fluid adding device. She could put 2 floz + 7 floz and read out 9 floz (it worked in imperial, but I’m sure it could have been converted to metric). Think she called it a jug.

6. tomás zerolo says:

Air definitely is a fluid. A compressible fluid [1].

If you look more closely, even that distinction is somewhat ummm… fluid (in the case of water, you’d have something like, perhaps, 1.9999999999 [2] instead of your 1.8.

At the end, that’s why digital electronics haves Schmitt triggers and things.

[1] https://en.wikipedia.org/wiki/Compressible_fluid
[2] Somewhat arbitrarily and roughly modeled on the compressibility of water, κT=4.6E-10 / Pa at 25°C

7. Osgeld says:

Great readers cant tell the difference tween a physical state and a physical property… Its been a good run but when hack a day readers fail grade school science its time to pack it in

8. mt21 says:

Now I understand the concept of a bit bucket!

9. David J Cuccia says:

Cool. But not ironic. Appropriate?

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