The challenge
Loop+ is a pressure-sensing mat that sits under a wheelchair cushion, monitoring pressure distribution to help prevent pressure sores over a full day of seated life. Its founder came to the problem through family experience of wheelchair use, and her early prototypes proved the need — but the units were unstable and the design could not be manufactured.
What we found
Three causes. The DC-DC converter could not supply the instantaneous current the ESP32 demanded on Wi-Fi transmit from three AA nickel metal hydride cells. The charge management was inadequate. And the low-cost battery holders were cutting through the cells' thin jackets, shorting them and causing them to heat. We kept the ESP32, rebuilt the power subsystem and its configuration around it, and improved how the units integrated with the software the team used to manage data acquisition remotely.
What we built
The mat itself was hand-soldered wiring looms that snapped at the joints and left a lumpy surface to sit on — a real problem in a product that exists to manage pressure. We replaced the loom with a custom flexible PCB backbone carrying eight resistive force transducers, read through an 18-bit analog front end: flatter, and far better to assemble. We also redesigned the housing that mounts at the rear of the wheelchair, and the industrial design around it.
The results
We delivered eight functional samples and the team carried their clinical trial work forward on stable hardware. Our assessment was that the product would ultimately be better served by lithium ion cells and a Bluetooth backhaul in place of Wi-Fi, which is power-hungry for a battery device of this size. The client's budget did not extend to that work, and the units as delivered were fit for the trial stage, with battery life short of what a commercial product would need.
