stepper_sc — STM32F411 Stepper Controller PCB

Single-axis stepper motor controller board built around the WeAct STM32F411CEU6 Black Pill v3.1.

Drives a CWD556 opto-isolated stepper driver (PUL/DIR interface) from MCU outputs via NPN buffer stage.

Block Diagram

24V ──── 78M05 ──── +5V ──── Black Pill (3.3V regulator on-board)
                              │
                    PB10 ─── R1/R2/Q1 ─── J2 (PUL → CWD556)
                    PB14 ─── R3/R4/Q2 ─── J3 (DIR → CWD556)
                    PA3  ─── J4 (Endstop L)
                    PA4  ─── J5 (Endstop R)
                    PA6  ─── J6 (Jog L)
                    PA7  ─── J7 (Jog R)
                    PB0  ─── J8 (Step L)
                    PB1  ─── J9 (Step R)
                    PB15 ─── J10 (Buzzer)

Hardware

Ref	Value	Function
U1	78M05	24V → 5V regulator
Q1, Q2	BC547	NPN buffer (PUL, DIR)
R1, R3	1kΩ	Base resistor
R2, R4	10kΩ	Base pull-down
C1	47µF	Regulator input bulk
C2, C4	100nF	Regulator decoupling
C3	100µF	Regulator output bulk
C5	100nF	Black Pill VIN decoupling
J1	2-pin screw	24V power input
J2	2-pin screw	PUL output to CWD556
J3	2-pin screw	DIR output to CWD556
J4–J10	2-pin screw	Signal terminals
J11A, J11B	1×20 header	Black Pill socket

Pipeline

Schematic and netlist are generated from firmware source — main.h is the single source of truth for MCU pin assignments.

firmware/Core/Inc/main.h
        │
        ▼ fw_to_net.py
howto_sch_and_then_api/stepper_sc.net
        │
        ▼ howto_sch_and_then_api/stepper_sc_gen.py
stepper_sc/stepper_sc.kicad_sch

Re-generating after pin changes

# Activate venv (needs kicad-sch-api)
source venv/bin/activate

# Step 1: netlist from firmware
python3 fw_to_net.py

# Step 2: schematic from netlist
python3 howto_sch_and_then_api/stepper_sc_gen.py

Setup

python3 -m venv venv
venv/bin/pip install kicad-sch-api

# KiCad symbol libraries — set path to your KiCad install
# e.g. /usr/share/kicad/symbols
ln -s /path/to/kicad/symbols kicad_sym

Firmware

See firmware/ for STM32 application source (Core/).

Requires ST HAL (Drivers/) — generate via STM32CubeMX or download from st.com.

Build:

cd firmware && make

Flash via Black Magic Probe:

arm-none-eabi-gdb -x script2.gdb build/stepper.elf

See doc/build-and-debug.md for full build, flash and debug instructions.