STM-Based 24 V I/O PCB

I need a compact STM-microcontroller board that runs from a single 24 V DC, 5 A supply and handles the mixed-signal I/O of a small machine. Inputs • five pulse channels for incremental encoders, each tolerant from 5 V to 24 V • three proximity-sensor channels, also 5 V–24 V but with on-board pull-ups Outputs • two high-side drivers that can source 12 V–24 V to energise solenoids • one logic output that drives a 230 V AC, 25 A solid-state relay • one buzzer line, 5 V–12 V • three indicator lines for green, yellow and red LEDs (5 V–24 V tolerant) Communication The board must appear on a PC as a USB device and route that USB link through an on-board USB-to-RS485 converter that ends in a DB-9 connector. The STM will then speak Modbus-RTU on the RS485 bus. Key requirements • choose only parts available in JLCPCB’s basic or extended libraries so I can order the board fully assembled • size and mounting hole placement suitable for a 100 mm × 100 mm 4-layer stack-up (if you need more area, tell me early) • robust 24 V input filtering, reverse-polarity and surge protection • clear silkscreen labelling, test points for every supply rail and UART • all high-side outputs protected against inductive kickback Deliverables (JLC-ready) 1. KiCad or Altium schematic and PCB project files 2. Gerbers, drill files, pick-and-place (CPL) and BOM with LCSC part numbers 3. PDF schematic, assembly drawing and a brief design note that explains jumper settings, connector pin-outs and RS485 termination options I will review the files against JLCPCB’s online viewer; once everything passes without error I release the final payment.