A handheld that measures in analogue and computes on Linux

The task

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 device. 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 be available in ten years' time.

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. We wrote our own Linux core drivers for signal acquisition and the controls; the customer-specific application and its interfaces sit on top of them.

The result

A handheld whose measurement chain the manufacturer can develop further itself: the drivers belong to the manufacturer, the Linux base comes from the Buildroot project, and changing the module remains a bring-up rather than a redesign.