Inside a cheap set of eBay digital calipers

For such a lightweight plastic measuring device, the resolution of 0.1mm or 0.01" and repeatability is quite astonishing. Whilst not being suited to a professional machinist, these units are ideal for ordinary measurements, including designing 3D printed components.

It should be noted that the quiescent current of these devices is around 18uA, even when off (the display goes off until movement is detected).
Some users are reporting a very short battery life, but a typical 100mAh (0.1Ah) button cell should be able to supply 0.00002A for a very long time. (Theoretically 100's of days.)

The linear capacitive encoder in these units is very impressive. The physical encoder is seemingly very simple, with the bulk of the work being done by the ASIC (Application Specific Integrated Circuit). It's very similar in its cost optimisation to the cheap, but super-accurate weighing scales.

I'm really impressed by the accuracy of these units for their price. They are very common on eBay for as little as £5 (about $7 USD).

Here's a generic search link for the USA:-
https://www.ebay.com/sch/i.html?_from=R40&_nkw=carbon+fiber+caliper&_sacat=0&_sop=15
Or for those in the UK:-
https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=carbon+fiber+caliper&_sacat=0&_sop=15
The standard search term is carbon fiber caliper.

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