AT89C2051 LED Clock Assembly Kit

Physically compact at 75 × 50 mm, this kit uses a green-soldermask PCB with white silkscreen for high contrast and durability across multiple student cohorts. Components include the AT89C2051 microcontroller (pre-programmed), four red 7-segment LED modules (common-anode), 11.0592 MHz HC-49/S crystal, 22 pF ceramic load capacitors, 10 kΩ potentiometer for optional contrast adjustment (though not used in default config), two 4.7 kΩ pull-up resistors for buttons, four 2N3904 transistors for digit selection, and 330 Ω current-limiting resistors per segment. Total bill of materials contains 28 discrete components — deliberately scoped to avoid overwhelm while covering all essential categories (logic, timing, interface, power). Operation follows a deterministic sequence: power application triggers firmware initialisation; internal timer begins counting; display multiplexing starts immediately; button presses generate external interrupts handled in dedicated ISR routines. Timekeeping resolution is 1 second; display update rate is ~200 Hz. No serial interface or debug port is exposed — encouraging reliance on visual output and systematic testing instead of console logging. Designed for scaffolded instruction, the kit supports tiered learning: Level 1 focuses on mechanical assembly and safety; Level 2 adds continuity and voltage testing; Level 3 introduces firmware analysis via provided assembly listing; Level 4 invites modification (e.g., changing time format or adding debounce delay) using freely available 8051 toolchains — creating a natural progression from consumer to creator.