This DIY Piezoresistive Sensor Matrix Measures Pressure Data to Ensure a Good Prosthetic Fit

For people who have amputated limbs, or who were simply born without them, prosthetics can be extremely helpful. But just making a prosthetic is an expensive undertaking, and adjusting them for a proper, comfortable fit can be very time consuming. Everyone person’s body is shaped a little differently, and the exact point of amputation can vary from one person to another. That makes it difficult to get a good prosthetic fit, but this piezoresistive sensor matrix can collect quantitative data to help with the process.

This project was created by Chris Coulston, who teaches computer engineering at Pennsylvania State University, and one of his students who is also named Chris. That student has an amputation below his knee, and uses a prosthetic leg. Unfortunately, that prosthetic often becomes painful to wear and he has to visit a specialist to adjust the fit. Those adjustments aren’t always beneficial, which results in a cycle of return visits. So he developed his own pressure sensor to gather data that could be helpful in attaining a more comfortable fit.

He showed his sensor design to Coulston, and the two decided that it could be improved upon to provide even more granular data. They were inspired by Marco Reps’ yoga-mat sized pressure sensor matrix, which we featured a couple of years ago. Their design follows the same basic principle, but on a smaller scale. Piezoresistive material is sandwiched between two flexible PCBs, and the resistance is measured at numerous points in the matrix. Pressure alters that resistance, which can be detected.

They then used a custom interface board to measure the resistance at those points. That, in turn, connects to a PIC18F26K22 development board that collects the data and can store many days worth on an SD card. The final step was to calibrate the sensor matrix, which was done with a custom-made test jig that applies pressure to the matrix. A scale on the other side measures the pressure, so they can determine how the sensor readings correlate to the actual PSI being applied. Ultimately, that should help Chris get a more comfortable prosthetic fit.