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Researchers build a ‘cost saving’ conductivity probe from a micro USB

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Two engineers have developed a cost saving, more robust alternative to the expensive conductivity probes used to measure fluid properties such as water density.

The new device has the potential to save costs in a range of applications that require water measurement and analysis.

According to a statement from UC Santa Barbara, Paolo Luzzatto-Fegiz, a mechanical engineer at the university, came up with the idea for the device after growing frustrated when the tip of his conductivity probe kept breaking. Made of four small platinum electrodes housed in glass, the probe tip was thin and highly sensitive, capable of making measurements in tiny volumes of water.

"They work very well," said Luzzatto-Fegiz, an expert in fluid dynamics. "But the tricky thing is that they are expensive in addition to being fragile, so it ends up being quite expensive to do complicated experiments in the lab.

Luzzatto-Fegiz teamed up with his best friend Marco Carminati, a microelectronics and sensors expert, to develop a solution. On a visit to Carminati’s home city of Milan, the two engineers set about designing and building a conductivity probe using ‘off-the-shelf’ products. The probe they created achieves close to the same sensitivity as the conventional one, at a fraction of the cost. At the same time it is versatile and robust enough to withstand ‘the occasional knock’.

The biggest challenge, according to the statement from UC Santa Barbara, was replicating the probe tip with its closely spaced electrodes. This was solved by cannibalising nothing more than a micro USB connector plug, the kind most people will have somewhere in their home.

"What you do is you essentially peel off the outer metallic shield and expose these gold-plated electrodes and they're perfect," said Luzzatto-Fegiz, who credited Carminati for the idea. "You can make the whole thing for a couple hundred dollars in your garage, in your free time."

The new device has been named Conduino, because it measures conductivity and is Arduino based. The device is modular and customisable, and can also be powered by USB, making it highly portable.

"Although the Arduino microcontroller is sometimes considered a toy in the scientific community, it is a fantastic tool for rapid prototyping a digital interface controlling the high-resolution analog circuit tailored on the USB electrodes," Carminati said. "Its combination with Matlab perfectly suits the need for tweaks and integration with the precious code controlling complex experiments, common to researchers in the fluid dynamics and oceanographic fields."

The development of the new sensor is detailed in the journal Sensors & Actuators B: Chemical.