🛠️ Build a USB Digital Calliper Interface with STM8S

Featuring a Fractional Inch Display App — Available on Microsoft Store

Whether you're machining, woodworking, or just love precision, digital callipers are a must-have tool. But what if you could take that measurement data and display it on your PC — with full decimal accuracy and familiar imperial fractions like “5/8″”?

In this project is a USB interface for a digital calliper using an STM8S microcontroller, and pair it with a custom desktop app that displays live measurements in both metric and imperial formats. The app even highlights common fractional inch values — just like commercial callipers do, but with more control and clarity.

Software

The companion application for this project is available on the Microsoft Store — no warnings from Windows about unknown publishers! You can download it here:

Several display modes:

Metric

Imperial

Calibration

🧠Programming the STM8S103F

The STM8S103F microcontroller needs to be programmed.

🧰 What You’ll Need:

ST Visual Programmer Download and install the ST Visual Develop IDE from STMicroelectronics — it includes the programmer tool.

ST-Link v2 USB Programmer This is required to upload code to the STM8S103F.

🔌 Connecting the ST-Link to the STM8S103F

The ST-Link can connect in two ways:

SWIM (Single Wire Interface Module) — this is the method we’ll use for STM8

SWD (Serial Wire Debug) — used for ARM chips, not applicable here

For STM8, you’ll need to connect four wires between the ST-Link and the STM8S103F:

3.3V - VDD (power)

GND

RST

SWIM

These connections are labelled on the back of the PCB.

Do not have it plugged into a USB when programming.

I have done a full Instructable here: Tim's Digital Calliper Interface : 11 Steps (with Pictures)