# Fluidic logic

I recently made a blog post about the analogy between fluid flow in pipes and analog electric circuits.  Of course, I’m not the first to think of this. It’s called the hydraulic analogy.  But it’s not just analog circuits for which this analogy carries over, the analogy works for digital electronics as well. That is you, can do logic gates hydraulically. This is called fluidics and there already happens to be designs for how to construct hydraulic amplifiers. With hydraulic amplifiers, you can do logical operations.

How does it work? A very small stream of fluid deflects a very large stream. First I’ll show you how to do a NOT gate, then an AND gate and together NAND.

NOT gate:Simply take the left outgoing tube as your output. Done.

AND gate:To do an AND gate, take the output of the first amplifier, the right side, and feed it into the large stream of the second amplifier. Now the second amplifier will only have a stream in the right hand side if both control streams are on. BOOM! An AND gate.

Together, you can make a NAND gate and NAND is universal for logic which basically means you can make a computer if you can make a NAND gate.

The RepRap project was how I first learned about 3d printing. It has the remarkable mission, in that I’m remarking about it, of printing all of the parts to make another printer. Wow. Well, in principle, all of the circuits can be replaced with pneumatic ones. And also, you know, it might make a cool theme for a sci-fi flick. Just imagine a 3d printer printing with a background of hydraulic valves, pumps and hoses. Generate a pressure difference with steam and you’ve made a steam punk wet dream.

Now I’m not suggesting that we start running our 3d printers this way. The point is, if push came to shove, 3d printers could print out much more of their parts than they currently do without the need to resort to printing new materials.

In honor of the RepRap project, I designed a printable version of the fluidic amplifier. You can find it on thingiverse here. You can test that it works using your mouth.

Instructions:Just print it out twice and hold it together, tape it together, screw them together or glue them together. Doesn’t matter how you do it. Just make sure they stay together. To test them, you only need to hold them together with your hands and blow through the power port and one of the output ports. I just tested it and between 70-90% of the air went through the right output port. Considering that I was holding them together with my hands and using my mouth, that’s pretty freakin’ good. 🙂

I should also point out that this thing was already patented in 1974.