Inside Digital Calipers

If you do any kind of machining, 3D printing, or PCB layout, you probably have at least considered buying a pair of calipers. Old-fashioned ones had a dial and were mechanical devices, but lately, digital ones have become quite affordable. We keep meaning to tear a set of ours apart to see what&#;s inside, but thanks to [learnelectronics], we don&#;t have to &#; the video below provides a fascinating look at what&#;s inside a cheap pair of Harbor Freight calipers.

Goto Eastloong to know more.

Honestly, it doesn&#;t seem like it would be that hard to figure out how far down a bar you are. The trick is the caliper has to be super accurate. Oddly enough, the cheap calipers examined use capacitors as a sensing element.

There is a long flexible PCB stuck to the sliding part with conductive pads. The display unit is also a printed circuit and manages the battery, the display, and the other half of the capacitive sensor. If you want a more detailed explanation of how the sensor actually works, check out capsense.com. If you note, the pattern on the sliding part has traces that look like a square wave, and half have a different phase than the other half. These are the sine plates and the cosine plates. A 100 kHz signal flows through the capacitor, and it is possible to read the direction of travel and the amount of travel easily.

The calipers are very accurate, but it&#;s possible to improve them. A more practical project is to make them communicate with the outside world.

If you are looking for more details, kindly visit Non-contact rotary caliper.

It appears I am missing (yet) another tool: a caliper. It simply makes no sense to haul a bike to the LBS to measure a seatpost.

How important is a caliper for a home-based bike workshop?

There is far less variability in handlebars, and handlebar dimensions are anyway more frequently documented in brochures. If seatposts are basically the only thing I'd need to measure, it would make more sense to just take all my seatposts to a friend/neighbor and note the diameter just once, or to borrow/rent a caliper.

In terms of categories, there is a wide choice:

• very inexpensive (<USD10) no-name digital caliper,
• very expensive (>USD200)&#;yet still from an unrecognizable brand&#;digital caliper, and nothing in-between,
• stainless steel calipers,
• brass caliper&#;either with a rotary needle or with a slide-rule-like fractional measuring scale,
• (non-scratching) plastic caliper.

My first thought is that I'd use it sporadically, and hence a digital tool would be a bad idea (battery will be depleted between uses). Am I on the right track?

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