UI (Urinary Interface)
Team: Alex Dodge, Ezer Longinus, Johnny Lu, Stepan Boltalin
24k Gold Plated Sensor Array
The “UI” is an exercise in dynamic fluid detection. To make the project exceedingly more silly we decided to deploy our fluid detector as an input device within a urinal in a men’s restroom. This would then provide feedback in the form of an elaborate LED light display to the user. Our final goal was to install two detectors so that the feedback could be reciprocated .
After initial attempts prototyping a cavity-based fluid detection matrix we realized that while the approach had many advantages, especially in the ability to fine tune the detection sensitivity, it soon became apparent that any metal conductor that we had on hand quickly became corroded in our saline test solutions during detection (essentially performing electrolysis). The electrodes would become so oxidized and corroded that they would soon stop conducting all together. We were able to make a very consistent cavity matrix by casting the negative of small bubble-wrap packaging material. Seen here is a test sample of our initial panel. Seen clearly is the darkened and corroded cathode wire in the center:
The only option: 24k gold. Gold is among the few metals that is fairly resistant to corrosion making it an ideal material to plate our electrodes with. We learned that while plating directly on top of copper is possible there is often a diffusion of copper atoms through the thin gold plate that can eventually lead to corrosion again. To prevent this we electroplated with Rhodium as an inert barrier layer.
While the gold plated sensor array has been very successful in detecting fluid, we soon realized that the larger problem was dispersing the fluid. Essentially our sensors would stay “ON” after exposure. We have been able to partially solve this with the application of a water repellant coating that causes fluid to quickly bead and roll off the sensor.
Further difficulties included our multiplexing system. We initially began with a repurposed keyboard multiplexer from an old PS2 keyboard. This seemed hugely convenient at first with an existing Arduino library, though the “one key at a time” condition of text entry keyboards led us to abandon this approach in favor of dedicated multiplexing circuits such as the CD4067B:
At present our detectors seem viable though our LED output matrices have proved to be more difficult than expected.
A functional two detector system should be possible.
This project was part of an experiment in project sharing dubbed “workflow management” in which the responsibilities of two projects were shared between two teams with the hope that more could be learned and accomplished by integrating two seemingly dissimilar projects. This approach proved to be very rewarding and at times essential as development on one project led us down avenues for the other that we might not have otherwise considered. In one case diagnosing an elusive bug in our fluid detection circuit.