Crack-the-Code Safe
Month 1 ships Oct 19. A new kit every month. Cancel anytime.
Project Overview
Crack-the-Code Safe is Month 3 of the Zynk Bots path: a working, PIN-protected safe you build and keep. Type your code on the 4x4 keypad, the 16x2 screen asks for the passcode and shows the result, a servo slides the lock open, and the LED strip and buzzer react to right and wrong guesses. You move to a third microcontroller, the Arduino Uno, try each part on a breadboard, then assemble everything into the safe's own case. Along the way you write the state machine that runs it, the single most important pattern in embedded software. No soldering needed.
Real-World Applications
ATMs and door entry panels
Cash machines, building door panels and hotel safes all read a matrix keypad and check a PIN, the same row-and-column scanning and code check you write for your safe.
Smart locks
Keypad and smart door locks use a small motor to move a latch once the right code is entered, just like the servo in your safe.
Appliances with modes
Microwaves, washing machines and alarm systems step through modes like locked, waiting, running and alarm. That's a state machine, the pattern that runs your safe.
Robot control panels
Industrial robots and machines have keypad front panels and run on state machines, so they only move when the right mode is selected.
Skills Developed
Skills you'll carry forward
State machines — the pattern you learn here — run Month 5's lamp and fan controller, and by Month 6 they power a four-state wireless household system.
See the month-by-month learning path →Project Prerequisites
Before starting this project, we recommend completing these foundational projects:
Months 1–2: Cyclone LED and Smart Alarm Clock (buttons, buzzer and display basics)
Recommended
A Windows, Mac, or Linux computer with a USB port for uploading code
Recommended
Learning Objectives
By completing this project, you will achieve the following measurable outcomes:
Program an Arduino Uno, a third microcontroller platform
Read a 4x4 matrix keypad by scanning rows and columns
Design a state machine with locked, entering, open and alarm states
Validate a PIN with arrays and compare sequences
Drive a servo motor to open and close a latch
Show prompts and feedback on a 16x2 LCD
Add sound and light feedback for right and wrong codes
Assemble and power a finished device
What's in the Kit
Everything you need to build your Crack-the-Code Safe, carefully selected and packaged
Arduino Uno
The classic Arduino board — bigger, sturdier headers and very forgiving to wire up. Used as the brain for projects designed for absolute beginners.
USB-C Cable
USB-A to USB-C cable for uploading code to your board and for powering and charging your project from a computer or USB charger.
USB A-to-B Cable
USB-A to USB-B cable for connecting the Arduino Uno to your computer to upload code and power it up.
RGB LED Stick (8 LEDs)
A short stick of 8 color-changing LEDs — same chip family as the ring, but in a straight line. Used in projects that need a row of independently controlled lights.
16×2 Character LCD Display
A two-line text display (16 characters per line) with a blue backlight. Connects to the microcontroller with just 4 wires. Used whenever the project needs to show short messages or numbers.
Buzzer
A small electronic buzzer that plays tones and simple melodies. Used in the Smart Alarm Clock and game projects. Wires are pre-soldered for easy connection.
On / Off Rocker Switch
A snap-in rocker switch for turning a project on and off. Pre-soldered with male pin headers on the wire ends for easy plug-in to the rest of the circuit.
18650 Rechargeable Battery (2600 mAh)
Rechargeable 3.7 V / 2600 mAh lithium-ion 18650 cell, the standard power source for the portable projects. Drop it into the holder and recharge it over USB through the project's charging board.
18650 UPS Booster-Charger (15 W)
All-in-one 18650 battery board: charges the cells and boosts their output to a steady 5 V, 9 V, or 12 V (up to 3 A), with uninterrupted power while charging.
4×4 Keypad
A 16-key membrane keypad with numbers, letters, and symbols. Used in the Crack-the-Code Safe for entering PINs and combinations.
Mini Servo Motor (SG90)
A small motor that turns to a specific angle on command (0–180°). Used in the Crack-the-Code Safe to operate the lock, and in any project that needs precise mechanical movement.
Jumper Wires — M/M (20 cm)
Multi-colored Dupont jumper wires with male pins on both ends. 20 cm long, 40-wire ribbon. A little extra slack for routing around enclosures.
Jumper Wires — M/F (20 cm)
Multi-colored Dupont jumper wires with a male pin on one end and a female socket on the other. 20 cm, 40-wire ribbon.
Jumper Wires — F/F (20 cm)
Multi-colored Dupont jumper wires with female sockets on both ends. 20 cm, 40-wire ribbon.
Breadboard (400 holes)
A solderless prototyping board with 400 contact holes. Plug components and wires in to build circuits without permanent soldering — pull them out and reuse for the next project.
Electrical Tape
PVC insulation tape for insulating and tidying wires inside enclosures.
Double-Sided Foam Mounting Pads
Pre-cut black foam pads with strong adhesive on both sides. Peel off the backing and press to mount the circuit board, battery pack and modules securely inside the enclosure.
M3 Screw — 6 mm
Short M3 machine screw (6 mm, black zinc-plated). Standard fastener for assembling the 3D-printed enclosures.
M3 Screw — 12 mm
Longer M3 machine screw (12 mm) for stacking enclosure layers or attaching speakers and battery holders.
Hex Key (for M3 screws)
Hex (Allen) key sized for the M3 screws — included so the project can be assembled at home without buying extra tools.
Crack-the-Code Safe — Enclosure
3D-printed case for the Crack-the-Code Safe. Has a hinged door and openings for the keypad and the servo lock.
Course Content
Course Content Coming Soon
This project is being prepared. Course lessons and content will be available once the project is fully published.
Safety Guidelines
Please review these safety guidelines before starting your project
Designed for ages 13+. We recommend an adult is present for the first power-up, when charging the battery, and when using tools.
Disconnect power before handling
Always disconnect power sources and unplug devices before assembling, modifying, or troubleshooting electronic components.
Keep away from water and liquids
Do not use electronic components or tools near water. Keep drinks and liquids away from the work area.
Follow manufacturer instructions
Read and follow all instructions provided with kits and components. Do not exceed recommended voltage or current.
Battery care
Charge the 18650 cells only on the UPS board in the kit. Stop using them and tell an adult if a cell gets hot, swells, leaks, or is dented.
Moving parts
Keep fingers clear of the servo and latch while the safe is powered, and don't force the door while it's locked.
Small parts
Screws and small components are choking hazards. Keep them away from younger siblings and pets while you build.
Not a real security device
This safe teaches how locks and codes work. Don't use it to store money, medicine or anything valuable.
Related Projects
Continue your learning journey with these recommended projects
Smart Alarm Clock
Smart Alarm Clock is Month 2 of the Zynk Bots path: a real bedside clock you build and keep. A 2.42-inch OLED screen shows the time, date and your alarm, a real-time clock module keeps accurate time, a touch sensor and buttons set the alarm and snooze, and an LED light bar and buzzer wake you up. You move up to a second microcontroller, the ESP32, try each part on a breadboard, then assemble everything on the clock's own circuit board and case. Along the way you write the timekeeping, alarm and scheduling code yourself. No soldering needed.
Cyclone LED
Cyclone LED is Month 1 of the Zynk Bots path: a reflex game you build and keep. A ring of 45 addressable RGB LEDs chases around the dial, and you press the button to stop the light on the target. Hit it and the game speeds up; miss and the round resets, with your level and high score on the built-in display. You start by trying each component on a breadboard, then in the final week put the whole game together on its own printed circuit board and case. Along the way you write and change the code yourself. No experience and no soldering needed.
Ready to Build Crack-the-Code Safe?
Month 1 ships Oct 19. Every month after that builds on this one.