Build a three-weapon fencing scoring box

An open design for foil, épée and sabre built around an inexpensive STM32F401 "Black Pill" board, with FIE timing and the rules hobby boxes usually skip.

What makes this design different

• Floor hits are ignored. It reads the piste and both ground lines, so a touch on a grounded metal strip does not light up.
• Blade contact is visible. The two weapon lines are driven alternately instead of from one fixed supply, which is what makes sabre whip-over detection possible.
• Lockout starts at the right moment: when the touch registers, not when contact begins.
• It never freezes. The lamps and buzzer are handled without pausing the scan, so it keeps watching while showing a touch.
• The rules are plain, testable code. The scoring logic has no hardware dependency and its tests run on any PC.

Timing it follows (FIE material rules)

In sabre the weapon's two socket contacts are joined at the guard, so the box treats that connection as normal, not as a fault.

What you need

• A WeAct STM32F401 "Black Pill" board (buy a spare), and optionally an ST-Link programmer
• 7 panel jacks (6 fencer lines plus the piste), seven matched 1 k resistors, 220 ohm resistors for the lamps
• Green, red and white lamps plus mode and fault indicators, an active buzzer with a small transistor driver
• Protection diodes on the fencing lines, two push buttons, perfboard, wire and a USB power supply
• Optional: logic-level MOSFETs and 5 V LED strip for bright, gym-visible lamps (Doc 12)
• Optional test rig: an Arduino Nano hit simulator (fires exact-millisecond touches) and a USB logic analyzer

Every part in plain language is on the store shopping list.

Build documents

Source code

The rules engine is plain C++. To run its tests on a PC: g++ -std=c++17 -O2 -o test test_scoring_logic.cpp scoring_logic.cpp then run test.

The official FIE Material Rules, which these timings come from, are published on fie.org.

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