Table of Contents
eSafe
Name: Dascalu Stefan-Nicolae
Group: 331CA
Introduction
eSafe is a digital lockbox implemented on an Arduino Uno. It uses a 4×4 matrix keypad for PIN entry, an SG90 servo for a mechanical latch, a DS1307 real-time clock (I²C) to enforce access windows, and a 16×2 I²C LCD to display status and time. Three wrong PIN attempts trigger an alarm tone and flashing red LED; valid entries drive the servo to unlock, light a green LED, and display “UNLOCKED.”
Hardware Design
Below are both the abstract block diagram and the detailed wiring schematic with an Arduino Uno:
Note on Simulation vs. Real RTC
In Tinkercad I used a generic 7-segment I²C display; the real build uses the DS1307 module on the same SDA/SCL, so no rewiring or code changes are needed.
Hardware Functionality
- Keypad: polled via Keypad library on GPIO
- Buzzer: tone/noTone alarm, driven directly from Arduino pin
- LEDs: status indicators with resistors
- Servo: 50 Hz PWM; relocked non-blocking after 5 s
- LCD/RTC: HD44780 via PCF8574; DS1307 battery-backed timekeeper
- ADC: internal 1.1 V band-gap → VCC monitor every 5 s; red LED blinks below 4.6 V
- Power: on-board 5 V regulator (~500 mA); peak draw ~270 mA
Pin-out Detail
| Component | Interface | Arduino pin | Direction | Rationale |
|---|---|---|---|---|
| Keypad row/col | GPIO | D2–D9 | input | Scanned periodically by Keypad library (no interrupts) |
| Passive buzzer | GPIO | D11 | output | direct drive with tone()/noTone() |
| Red LED | GPIO | D13 | output | Built-in LED pin |
| Green LED | GPIO | D12 | output | Digital status LED (no PWM on D12) |
| Servo SG90 | PWM | D10 | output | attach() supports D10 |
| LCD I²C | I²C (TWI) | A4/A5 | bidir | Hardware Wire bus |
| RTC DS1307 | I²C (TWI) | A4/A5 | bidir | Shares same TWI bus |
| ADC (VCC monitor) | internal ch 14 | — | input | 1.1 V band-gap reference |
Bill Of Materials
| Component | Purchase link |
|---|---|
| Arduino Uno R3 (ATmega328P) | https://www.optimusdigital.ro/ro/placi-avr/4561-placa-de-dezvoltare-compatibila-cu-arduino-uno-r3-atmega328p-atmega16u2-cablu-50-cm.html |
| 4×4 Matrix Keypad | https://www.optimusdigital.ro/ro/senzori-senzori-de-atingere/470-tastatura-matriceala-4x4-cu-conector-pin-de-tip-mama.html |
| DS1307 RTC Module (I²C) | https://www.optimusdigital.ro/ro/altele/4746-modul-ceas-in-timp-real-ds1307.html?search_query=Modul+Ceas+in+timp+real+DS1307&results=3 |
| LCD 1602 I²C Blue Backlight | https://www.optimusdigital.ro/ro/optoelectronice-lcd-uri/2894-lcd-cu-interfata-i2c-si-backlight-albastru.html |
| SG90 Micro-Servo | https://www.optimusdigital.ro/ro/motoare-servomotoare/26-micro-servomotor-sg90.html?search_query=Micro+Servomotor+SG90+90° |
| Breadboard + jumper wires + LEDs + resistors | https://www.optimusdigital.ro/ro/kituri/12026-kit-plusivo-pentru-introducere-in-electronica-0721248990075.html |
Photos and video of the eSafe project
Software Design
Implementation Status
- ~400 lines of custom C++ on Arduino Uno integrating all core features
- PIN entry with 4×4 matrix scan, three-strike alarm, and time-based lockout fully tested
- Live clock updates, non-blocking unlock/relock, and persistent last-unlock log verified in hardware
- Real-time VCC reading via ADC; value streamed to Serial Monitor and low-battery LED alert
Library Choices
| Library | Purpose | Justification |
| Wire / RTClib | I²C bus & DS1307 driver | proven reliability, minimal API for RTC access |
| LiquidCrystal_I2C | HD44780 LCD over I²C | reduces wiring and boilerplate, easy print() API |
| Keypad | matrix scan & debounce | built-in interrupt support and debounce logic |
| Servo | SG90 control | official Arduino, handles PWM timing internally |
Novelty & Lab Integration
- PWM servo control (Lab 3 – Timers/PWM): SG90 latch driven at 50 Hz; non-blocking auto-relock with `millis()`.
- Supply-voltage monitor (Lab 4 – ADC): reads the 1.1 V band-gap on channel 14 every 5 s, prints VCC on Serial Monitor, blinks red LED when VCC < 4.6 V.
- Shared I²C bus (Lab 6 – I²C): DS1307 RTC and PCF8574 LCD expander operate on the same SDA/SCL lines.
Architecture
1. updateDisplay()
- called once per second (via `millis()`), updates HH:MM:SS, renders PIN asterisks or “Last HH:MM”
- never blocks, so UI remains responsive
2. handleKey()
- ‘C’ clears entry, digits append to buffer (with asterisks), ‘D’ validates PIN
- on correct PIN, calls `unlockDoor()`; on wrong, increments counter or triggers alarm
3. unlockDoor()
- moves servo to unlock angle, lights green LED + buzzer for 1 s
- sets `lockRestoreMs = millis() + 5000` for non-blocking relock in `loop()`
- logs timestamp in `lastUnlock` for display
4. loop()
- checks `millis()` vs. `lockRestoreMs` to relock servo without pausing
- updates display every second and polls keypad
- validated by toggling between allowed/outside hours and using a stopwatch for timing
Calibration & Optimizations
- Keypad debounce is handled inside the Keypad library (no Timer2 code needed).
- Servo angles: adjusted to 20° (unlock) and 110° (lock) for mechanical reliability.
- Blocking calls minimized: only a 1 s buzzer delay remains; all longer waits use non-blocking `millis()` logic.
Conclusions
eSafe showcases the seamless integration of three core microcontroller features: PWM (servo latch), ADC (live VCC monitoring), and I²C (RTC + LCD). All time-sensitive tasks are handled with non-blocking `millis()` logic, so the user interface stays responsive while the clock remains accurate.
Bibliography & Resources
- ATmega328P Datasheet
- DS1307 RTC Datasheet
- LiquidCrystal_I2C Library Guide
- Keypad Library Reference
- PlatformIO Documentation