A handheld that measures in analogue and computes on Linux

The brief

Handheld instruments in measurement technology have to do two things at once: capture the sensor signal and give the user a device that handles like a modern mobile. The client wanted both in one enclosure, battery-powered and with wireless communication.

Analogue signal conditioning and digitisation were customer-specific; the computing power was to come from a module that will still exist in ten years.

The solution

The system-on-module is a Raspberry Pi CM4, powered from a lithium-ion pack in 2S1P. The display is an LCD with capacitive touch and gesture control, plus a nine-key membrane keypad and USB OTG.

The software runs on Buildroot. For signal acquisition and the controls we wrote our own Linux core drivers; on top sit the customer-specific application and its interfaces.

The result

A handheld whose measurement chain the manufacturer can carry on alone: the drivers are its property, the Linux base comes from the Buildroot project, and a module change stays a bring-up rather than a redevelopment.