Edit: there is now a HaD project for the STM8S001J3RS485 breakout!.

It's been a while since I last worked with STM8S001J3 chips - ST's contested take on SO8 ATtiny85-like µCs.

The STM8S001J3 is a member of the "STM8S Low Density" family but it's based on the "STM8S Access Line" cross-breed STM8S903 that offers some (undocumented) goodies.

I ordered a 10pcs lot for $2.90 including shipping, and decided to make small RS485 nodes (e.g. for MODBUS RTU)  with DS1621S thermometer chips that I happen to have lying around.

I made my last PCB with KiCad5.0 - updating to the latest version, especially the library handling, required some reading (I'm now using 5.1.4).

A µC with merrily 5 GPIO pins is a good shield against feature creep, but the following things "had" to be included:

• narrow PCB for a cylindrical sensor with less than 8mm diameter
• 5V supply, 3.3V internal power supply
• basic signalling LEDs
• most GPIOs, including I2C bus and an analog input available on a header

The design is really simple:

Components occupy both sides of the PCB of 34mm x 1/4" (minimal width supported by @oshpark ).

On the front side is the STM8S001J3M3, a LDO regulator and some caps:

The RS485 transceiver and the thermometer chip live on the backside:

The board has two intended applications: either a stand-alone bus coupled temperature sensor, or a minimal µC component, e.g. for a quick perfboard design.

I ordered from @oshpark - uploading my KiCad 5.1.4 file worked right away, and creating Gerber files wasn't necessary!

Files and docs are, as usual, on GitHub.