Custom Interface Adds USB And Wi-Fi To Digital Calipers

A digital caliper connected to a tablet computer

Although old-school machinists typically prefer the mechanical vernier scale on their trusty calipers, many users nowadays buy calipers with a digital readout. These models often come with additional features like differential measurements, or a “hold” function for those situations where you have to maneuver the instrument somewhere deep inside a machine. Another useful feature is a data link that lets you log your measurements on a computer directly instead of manually entering all the values.

The VINCA-branded caliper that [Liba2k] bought has such a data link feature, which requires a USB adapter that’s sold separately. There is a micro-USB connector on the tool itself, but instead of implementing a USB interface, this is used to carry a proprietary serial protocol — a design decision that ought to be classified as a felony if you ask us. Rather than buying the official USB adapter, [Liba2k] decoded the protocol and built his own interface called VINCA Reader that can connect through either USB or Wi-Fi.

The serial format turned out to be a simple serial bus that clocks out 24 bits at a time. In order to adapt its 1.2 V signal level to the 3.3 V used by an ESP32, [Liba2k] designed a simple level shifter circuit using a handful of discrete components. The ESP can communicate with the computer through its Wi-Fi interface, for which [Liba2k] wrote a spreadsheet-like application; alternatively, an ordinary USB cable can be connected to emulate a keyboard for use with any other software.

With its added Wi-Fi feature, the VINCA Reader is actually more complete than the official USB adapter, and will probably be cheaper as well. The serial interface appears to be common to all caliper manufacturers, although many went for a more sensible connector than micro-USB. An automated readout system is particularly handy if you have to make thousands of similar measurements.

25 thoughts on “Custom Interface Adds USB And Wi-Fi To Digital Calipers

      1. Yeah, don’t try it, it will fry it. This is the exact solution for that. I got mine because I wanted to use the feature of display on the monitor and found out afterwards that I had to buy the module separately for damn near the same price as the calipers. I’m really looking forward to using this setup.

        1. My issue over the past many years hasn’t been the tool – it’s been the battery. It’s hard to find non-counterfeit batteries for a reasonable price. Most button cell batteries are low quality junk and leak internally. The give away is that the bulge on the flat side. If there is *any* wobble when you put it on a flat surface, it’s dead.

          It’s either pay high retail prices or take your chances with the cheap bulk stuff…

      1. A friend recommends flipping the batteries upside down instead of removing—much easier to find them this way :)
        The battery maintains the memory of the absolute position, so you will have to re-zero it. Normally not a big deal but it would be nice if the cheap end of the market moved to a more modern tech–the chips they currently use were designed many years ago, and didn’t have the low power and non-volatile memory that would solve these problems.

      1. I dont know if I would consider Wiha as “crappy”, overpriced for the level of quality they offer, yes absolutely. As far as the “made in Switzerland” sentiment goes, in regards to precision machine tools and measuring instruments, I’d go with Japanese made almost exclusively.

    1. Many have that design flaw, which is also present on a lot of flashlights with multi functionality (e.g. some circuit for brightness, strobe), it’s because they don’t implement a proper full cutoff and their sleep mode vamps juice while doing nothing.

      I find the better brands do it properly. I bought a Mitutoyo knockoff that has never been found dead in over two years. Brand is iGaging , cost around $45.

  1. More sensible than micros usb? A connector requiring 3d printer or tracking down the part, or and connector and cable found in scrap bins everywhere.
    Wrong to assume the connector = the signal interface

    1. My smart thermostat knobs have a USB micro socket on the side. However, they are used for a proprietary analog sensor and have the voltage (3V) on the inner pin pair instead of the outer (which means it’ll go to the data pair of any normal USB device you’ll plug into it).

      1. Eeek. I’ve used common connectors (like USB-A or USB-C) for non-standard connections before because they’re often cheaper and cleaner than traditional hobby connectors, plus cables are cheap .. but I always make a point to key/modify them in a way they can’t be inadvertently plugged into something else.

  2. “old-school machinists typically prefer the mechanical vernier scale”? I’m willing to bet that few old school machinists can read the vernier scale on their calipers. Digital calipers are so much easier to read and if you do serious machining, you can afford a set that will rival vernier accuracy. I still like dial calipers for the convenience of no batteries though…

    1. I like verniers for very quick and dirty measurements in the workshop, but I’m a mechanic not a machinist, so long as I can tell to 1/2mm accurately that’s plenty. If I need to measure accurately (in my world that means thou)I tend to use proper micrometers, as at that level I don’t trust or find calipers that repeatable

  3. That’s not a half bad idea .. I never use the USB out functionality that is common on a lot of my measurement tools because it’s often cumbersome to have to be tethered to a PC.

    With how small ESP-32 devices are, this could probably be rolled into a really tiny connector that plugs in and sends the output. I could see it being adapted to a lot of different devices (anemometer, multimeter, etc.).

  4. I suspect its the circuitry to monitor position change that draws the power when off. NV memory doesn’t help if you move the slider. Would require a re-zero. I zip tie a AAA battery holder to the back of the cheap vernier and run 2 wires to the outper power pins of the funny data socket. Typically get 4 years battery life on a single AAA battery. Multiple cheap verniers around. If I bought quality verniers I’d have to treat them better.

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