A 3-digit safe lock built entirely with logic ICs and discrete electronics —
no firmware, no microcontroller, just clever CMOS design.
This project demonstrates a purely hardware implementation of a digital safe lock.
The system uses shift registers (CD4015), counters (CD4516), 7-segment decoder (CD4543),
and a 555 timer for pulse timing — all wired to validate a 3-digit code.
Main Features:
- 3-digit code detection logic
- Unlock pulse generated by a monostable 555
- Noise-resistant button inputs (debounced)
- Output driver via logic-level MOSFET (BS170 / IRLZ44N)
- Completely self-contained CMOS circuit
| Type | Location | Description |
|---|---|---|
| 📘 Schematics & PCB | schematics/ |
KiCad project files and exported diagrams |
| 🧾 Documentation | docs/ |
Full project book, presentation, and poster |
| 🎥 Media | media/ |
Video demo and photos of the build |
| 📈 Measurements | measurements/ |
Oscilloscope captures and test data |
|🎬 Click here to watch the demo video
- Shift Register (CD4015): Stores the 3-digit input sequence
- Logic Comparator: Checks for the correct code pattern
- 555 Timer (Monostable): Generates a 1-second unlock pulse
- MOSFET Driver: Activates solenoid or relay for lock mechanism
- Debouncing Network: RC + Schmitt Trigger ensures stable input
| Parameter | Measured Value |
|---|---|
| Unlock pulse width | 1.1 s |
| Solenoid current | 0.42 A |
| Supply voltage | 12 V |
| Logic section | 5 V regulated |
- KiCad 9.0 for PCB design
- Multisim / Breadboard testing
- Oscilloscope for pulse timing
- Soldering and hand-wiring for prototyping
Asaf Refael Dabush
Electrical & Electronics Engineering
Ariel University — 2026
Released under the CERN Open Hardware License – Strongly Reciprocal (OHL-S).