# Anderson’s Water Computer Springs A Leak and That’s Okay

Glen Anderson’s created an analog computer that uses water to demonstrate digital logic

A computer that uses water instead of electricity? That’s what Glen Anderson and his daughter, Dale, are demonstrating at Maker Faire Bay Area this weekend. He invites kids to fill buckets and dump them into one of four water tanks. On Friday, I asked him how it was going. “I am adding 1 and 1 but getting 1,” he said. Something was wrong and he was working to fix it.

Glen said his goal for the project was to demystify how computers “think”.

Glen showed off his project at Maker Faire in 2019 and he’s back this year with a set of posters explaining how they work.

I was a CPU designer in the 1990’s in Silicon Valley. I bragged to my 4 young girls at the time that I would be famous someday for the water computer that I tinkered with on and off during their childhood, thus the tongue-in-cheek name. I worked on cool things like a hardware divider and square root!

I’m a EE from Berkeley, and there’s long been this analogy of height of water meaning voltage for analog circuits, you can model a lot with high fidelity including capacitance and inductance etc, even AC effects. I always thought there should be a digital version of this analogy showing how neat it is to perform digital logic when all you have to work with is this magic 3-terminal device called a transistor (or vacuum tube before that). I wanted to demystify how computers work. I mean, it’s complicated but also understandable.

The key is this ping pong ball that floats in a “high voltage” (water pressure) and controls a gate flap o-ring thing that connects source to drain or not. This is like the “semi” in semi-conductor. The channel in a transistor conducts only when there is a voltage present at the gate terminal. Same for my water transistor.

So then I use that to build a 4-bit adder using standard logic techniques with a NOT and NOR gate. It uses 65 transistors total to add two 4-bit numbers such as 9+12.

Different ages react differently. Little kids just like to play with the water and tubes, and as they get older they will figure out the NOR (NOT_OR) logic of the gate by trying inputs. And then some try to understand the whole adder, more complex functions like the XOR function needed to produce the sum bit. In 2019 we had some kids hang with me all day just because they were attracted to the mechanism and helped me with the water pumping which I’ve kept manual on purpose to make the exhibit interactive (and fun–no pump and electricity needed)

There are a few water logic demonstrations on the web (youtube) that are neat, but a fundamental difference is mine are powered gates like in a real computer. The water doesn’t just flow from up high and flow all the way down using the signal itself which degrades. So my architecture is scalable and you can do things like perform memory functions (flip flops and latches). I even filed a provisional patent and let it expire on purpose just to put this invention in the public domain. I’ve thought of making it a product toy but that’s a lot to take on. I think this thing is unique in the world!

Come see Anderson’s Famojus Water Computer at Maker Faire Bay Area on Mare Island.

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### Dale Dougherty

DALE DOUGHERTY is the leading advocate of the Maker Movement. He founded Make: Magazine 2005, which first used the term “makers” to describe people who enjoyed “hands-on” work and play. He started Maker Faire in the San Francisco Bay Area in 2006, and this event has spread to nearly 200 locations in 40 countries, with over 1.5M attendees annually. He is President of Make:Community, which produces Make: and Maker Faire.

In 2011 Dougherty was honored at the White House as a “Champion of Change” through an initiative that honors Americans who are “doing extraordinary things in their communities to out-innovate, out-educate and out-build the rest of the world.” At the 2014 White House Maker Faire he was introduced by President Obama as an American innovator making significant contributions to the fields of education and business. He believes that the Maker Movement has the potential to transform the educational experience of students and introduce them to the practice of innovation through play and tinkering.

Dougherty is the author of “Free to Make: How the Maker Movement Is Changing our Jobs, Schools and Minds” with Adriane Conrad. He is co-author of "Maker City: A Practical Guide for Reinventing American Cities" with Peter Hirshberg and Marcia Kadanoff.

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