This Soft Clock Drives Its Display With Pneumatic Logic

Electrons exist big. We use them to move cars, light cities, and, of course, count. But computing is not limited to the world of electronics. And switching to other non-electronic areas can open unique advantages: Photonic chips, for example, process information with light while generating less heat. Another compelling method is fluidics, which uses compressed gases or liquids to build logic circuits. Pioneered in the 1960s but sidelined by microchips, the field re-emerged in the 1990s as “microfluidics.” This approach aims to shrink laboratories to a single chip by creating micro-fluidic channels with integrated micropneumatic control systems.

Today, there is a second fluidic revival, this time in the domain of soft robots. Scaling microfluidic designs down to the millimeter scale (millifluidics) enables the high flow rates required to drive robotic actuators. These robots take advantage of the non-linear behavior of soft materials to create lifelike movements and safe interactions, often using pressurized air.

By building systems that “think” with the same air that powers them, we can greatly reduce the need for large electronic-to-pneumatic interfaces. This is the focus of my Soiboi Studio robotics lab. With the millifluidic concept, I have gradually scaled the complexity of my designs. What started as a simple oscillator recently evolved into a watch with a sleek, four-digit, seven-segment display.

What is Millifluidics?

Building on microfluidics research from the early 2000s and recent developments from the Grover Lab at the University of California, Riverside, I developed millifluidic devices using conventional 3D printing and silicone casting. The basic structure is simple: A flexible membrane is sandwiched between rigid layers embedded with networks of air channels.

Just as electronic devices rely on varying electrical power, these fluidic circuits operate on the pressure difference between atmospheric pressure (logical 0) and the near vacuum around -60 kilopascals of relative pressure (logical 1). Applying negative pressure means that the membrane is pulled into open spaces. This creates strong signals that allow me to replicate the electronic building blocks.

A metallic silicone membrane forms the face of the watch [top]while behind it sit 3D printed millifluidic blocks [middle rows]. Arduino Uno controls driver boards that use solenoids, which are connected to valves connected to a vacuum pump. [bottom row].James Provost

Although liquid barriers are easily identified by adjusting the channel geometry, the heart of the system is a valve that simulates a metal-oxide-semiconductor field-effect transistor, or MOSFET. This vacuum “transistor” consists of a two-chamber flow layer (source and drain) separated by a central valve seat and a control layer containing a cavity (gate). The membrane runs between the flow control layers and usually prevents the flow of air between the well and the drainage chambers. To open the transistor, a vacuum is applied to the gate chamber, sucking the membrane from the hole and lifting it from the seat. This opens the way for air flow, which is equivalent to closing an electrical circuit. By putting a small hole in the membrane, I made a check valve—a fluid like diode. By combining transistors and resistive “pull-down” channels, I can build a complete logic gate framework.

The first microfluidic designs that inspired me were made of etched glass and etched acrylic. Adapting it to a standard 3D printer requires the reengineering of logic and the mastery of two important manufacturing techniques.

First, I need airtight prints, however printed plastic is notorious. By printing at high temperatures, slow speeds, and slow extrusion, I was able to fill very small gaps. If you use a transparent filament, there is a practical visual indicator: The more transparent the plastic, the less its porosity.

Second, I used glass in my print bed. By printing the top and bottom rooms directly on this bed, I got the surface to be mirror smooth. This finish is essential for creating reliable, airless signs. A 0.3-millimeter silicone membrane is placed between the layers and secured with screws.

How Does a Smart Watch Work?

The clockface is an embossed silicone membrane. Half of each digit is made up of a small cavity underneath. When air is expelled from this space, the membrane is sucked in to create a curved cavity; when atmospheric pressure is restored, the silicone rises back to the surface. The result is a lively, lively movement.

The “brain” of the watch is the Arduino Uno, while the fluidics greatly reduces the hardware footprint. A four-digit, seven-segment display with two dot dividers would require 29 solenoid valves for direct control. My watch only needs 11 valves.

A pneumatic transistor is closed when its upper control chamber is under air pressure [top]. When air is removed from the control chamber, it lifts the membrane, which allows air to flow between the lower flow chambers and turn on the transistor. [bottom]. James Provost

To understand how it works, consider a standard four-digit, seven-segment LED display. This also uses 11 pins to drive its numbers. (For clock displays, an extra pin is needed to drive the divider dots.) Every digit is connected to a shared data bus with seven lines, one per segment. The four control lines select individual digits. Only one digit is illuminated at a time, and scrolling the digits at least 50 times per second creates the illusion that all four are illuminated simultaneously.

Such high-speed switching is not possible with air. Instead, I rely on memory. Each component acts as a capacitor: By discharging its cavity (logic 1), you “charge” the component; by restoring the atmospheric pressure (logic 0), you remove it. Thus, each digit acts as an independent 7-bit memory. If the system does not have enough air, the segments retain their shape for a few seconds.

Like an electronic display, the system uses a seven-line data bus. Each line connects to a solenoid valve that supplies vacuum or air pressure. To select the individual digits, I placed a fluic transistor between each component and its data line. All transistors’ control inputs for a given digit are combined into a single “write power” line connected to its solenoid valve. Activating this valve allows me to write data to the corresponding digit memory.

The watch updates one digit per second, meaning a full cycle on the face takes 4 seconds. This circuit also drives the separator dots: A set of fluidic diodes connect the enabling lines to the dot holes. Therefore, as each digit is guided, the dots automatically click.

This display is more than a clock; is a soft robot that happens to tell time. By loading the calculation into the same wind that powers the movement, the watch approaches a new class of machines that are lighter, lighter, and more compact. I am currently making a guide to getting started with vacuum-powered logic and may release a more refined version of this watch in the future. Watching silicone skin morph serves as an interesting reminder that not every concept needs silicon; sometimes, all you need is flexible silicone and airflow.

This article appears in the June 2026 issue of “Soft Watch.”