Standalone LCD Countdown Timer with Beep

I want a compact, standalone countdown timer that anyone can set for up to 60 minutes, on seconds level and easily read on a 7-segment LCD screen. Once the count reaches zero the unit must emit three clear, evenly-spaced beeps, then stop automatically.

Key requirements
• Hardware is fully self-contained; no external controller or larger system will be available.
• Display: 7-segment LCD, bright enough for indoor daylight viewing.
• Maximum duration: 1 hour, adjustable in whole-minute and second level.
• Audible alert: exactly three beeps at timeout, each about one second apart, loud enough to notice in a small room.
• Intuitive buttons or rotary knob to set, start and reset.
• Runs on standard batteries (coin cell). Power draw should allow several months of occasional use.

Deliverables
1. Schematic, PCB layout (KiCad or Eagle), and complete BOM.
2. Microcontroller firmware source (Arduino-compatible or bare-metal C) with build instructions.
3. Brief user manual plus assembly guide so the unit can be reproduced or handed to a manufacturer.
4. Demonstration video or clear photos proving the prototype counts down and triggers the triple-beep alert.

Acceptance criteria
• Accurate timing (±1 s over the full hour).
• Display remains readable throughout the countdown.
• Beeper sequence meets the 3-beep spec without extra tones.

Feel free to suggest component substitutions if they simplify sourcing or extend battery life, as long as the core functionality above remains intact.