This guide has revisited a previous project using more powerful and feature rich hardware. The switch to a Feather M4 Express has allowed the use of a feature-rich device coded in CircuitPython. The Feather's generous I/O capabilities has made possible the use of an eInk display which gives the ability to display readings as well as informative and warning text. The Feather also provides in-place battery charging which makes the device far more convenient.
There are a few ways to expand the project. First is making a printed enclosure that extends or mounts on the jar lid. Next is making a custom PCB rather than using hand-wired perf-board construction. Another direction is to enhance the display. A larger font would help with legibility, as would some icons.