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!