This is an old revision of the document!
Smart Clock on the AVR Platform
Student: Ilie Lucian-Alexandru
Grupa: 331CB
Introduction
The smart clock described in this project is a stand-alone device built around an AVR micro-controller (an Arduino-compatible UNO board). It continuously shows the time and date on a 0.96″ OLED display; it beeps briefly at every full hour; after 19:00 it gradually lights two LEDs acting as the hour- and minute-hands; and it adapts LED brightness to the room light level using an LDR sensor. The purpose of the project is to demonstrate features taken from at least three PM laboratories—Timers & ISR (Lab 2), PWM (Lab 3) and the I²C bus (Lab 6)—inside a useful, easy-to-demonstrate gadget. It also gives hands-on experience with an I²C OLED/LCD, a DS3231 RTC module and simple peripherals (LED, buzzer, LDR). The idea came from the fact that most low-cost electronic clocks drift by several minutes per month and have fixed brightness. By integrating a precision RTC and PWM/ADC control logic we eliminate these drawbacks. The clock is useful at home as a real gadget, can be easily extended (multiple alarms, temperature display, Bluetooth connection) and helps consolidate embedded-systems skills.
General Description
Smart-clock implementation on the AVR platform
The project is organized around an Arduino UNO R3, which acts as the brain of the system and links all modules. On the I²C bus two devices are connected: a DS3231 real-time clock, from which the micro-controller reads highly accurate time and date, and a 0.96″ OLED display where this information is shown permanently. Two 5 mm LEDs, driven by PWM outputs, work as the clock “hands” and light up gradually after 19:00, indicating the passage of time without being intrusive during daytime. One more LED, a RGB one, is used with D9/D10/D11 pins with PWM for breathing effect and colour cycling. A passive buzzer, connected to a third PWM channel, emits a short beep at every full hour; the 1 kHz tone is generated by a hardware timer that starts and stops automatically. The ambient-light level is taken from a photo-resistor (LDR) on an analog pin; the ADC readings are used to dim the LEDs when the room is well lit.
Hardware Design
List of materials for the smart clock:
- Arduino UNO R3 development board (CH340 compatible)
- DS3231 RTC module + CR2032 battery
- 0.96″ OLED display, I²C (SSD1306)
- MB102 breadboard, 830 tie-points
- Male-to-male jumper-wire set (≥ 65 leads)
- Passive buzzer, 5 V
- Red 5 mm LED – hour indicator
- Green 5 mm LED – minute indicator
- Common-cathode RGB LED, 5 mm (+ 3 × 220 Ω resistors)
- 220 Ω resistors × 2 (for the LEDs)
- 6 × 6 mm tactile button (SET)
- Photo-resistor (LDR) GL5528
- USB-A ↔ USB-B cable (programming & power)
- 5 V / ≥ 1 A PSU (phone charger)
Current hardware implementation status:
- All modules are wired on the breadboard and have been tested both individually and together
- DS3231 RTC keeps accurate time (drift \< ± 1 s / day)
- SSD1306 OLED shows the current time + ambient-light level (“Light level:”) once per second
- LDR reacts correctly (0 – 1023) and is used to drive a PWM brightness control
- LEDs:
- Red – blinks at 1 Hz (handled by a Timer1 ISR)
- Green – lights for 1 s whenever the minute changes
- RGB – PWM “breathing” effect; switching colours on BTN press
- Buzzer plays short beeps and a longer “gong” on each full hour
- All three push-buttons operate with `INPUT_PULLUP` and falling-edge detection
| Nr. | Component | Functional role in project | Pin / Library |
| 1 | Arduino UNO R3 | MCU + Timers/ISR + PWM + I²C master | — |
| 2 | RTC DS3231 (I²C) | Keeps real-time clock, internal temperature, alarm | RTClib |
| 3 | 0.96″ OLED SSD1306 (I²C) | Displays time, lux and LED mode | Adafruit_SSD1306 |
| 4 | Photo-resistor (LDR) + 10 kΩ divider | Measures ambient light (auto-dimmer) | A0 |
| 5 | 5 mm LED (red) | Second indicator (Timer ISR) | D5 |
| 6 | 5 mm LED (green) | 1 s flash whenever the minute changes (PWM-ready) | D6 |
| 7 | RGB LED | PWM “breathing” effect; 7-colour cycling via PWM | D9/D10/D11 (PWM) + 3 × 220 Ω resistors |
| 8 | Passive buzzer | Beep feedback & hourly gong | D3 (tone) |
| 9 | BTN HOUR | Increment hour | D2 |
| 10 | BTN MIN | Increment minute + beep | D4 |
| 11 | BTN MODE | Toggle blue-LED mode | D7 |
| 12 | Breadboard + Dupont leads | Rapid prototyping | — |
| 13 | Resistors 220 Ω / 10 kΩ | LED current limiters / LDR voltage divider | — |
Pin mapping:
- I²C bus (RTC + OLED) — pins SDA / SCL (dedicated I²C lines, on-board pull-ups)
- LDR (photo-resistor) — A0 · 10-bit ADC input
- Red LED — D5 · toggled by Timer1 ISR at 1 Hz (no PWM needed)
- Green LED — D6 · digital OUT / PWM-ready – flashes for one second each minute change
- RGB LED — D9/D10/D11 · hardware PWM used for smooth *breathing* effect and colours cycling
- Buzzer — D3 · `tone()` uses Timer2 for precise frequency generation
- BTN HOUR — D2 · INT0-capable input (configured with `INPUT_PULLUP`)
- BTN MIN — D4 · digital input (`INPUT_PULLUP`)
- BTN MODE — D7 · digital input (`INPUT_PULLUP`)
- PWM-capable pins (D3 / D5 / D6 / D9 / D10 / D11) were selected so they don’t clash with the I²C bus (A4/A5) or the UART lines (D0/D1)
Electric scheme
The following diagram shows all components connected on the breadboard, including the RTC, OLED, LDR, 3 LEDs (Red, Green, RGB), passive buzzer, and 3 buttons.
Connected components & functionalities
The following pictures show the physical assembly of all modules connected on a breadboard:
- OLED SSD1306 displays the following information, updated every second:
- Current time in format `HH:MM:SS`
- Ambient light level (lux value from LDR sensor)
- Current RGB LED mode (`colorIdx`) + OFF status if index is 0
- Dim mode status: “Dim mode: ON” or “Dim mode: OFF”
- RTC DS3231 is used to keep accurate time with ±1s/day drift
- LDR sensor is placed on the breadboard and provides real-time ambient light readings (0–1023)
- Used to activate automatic dimming if value is below 400
- Push-buttons (HOUR, MINUTE, MODE) are connected to D2, D4, D7 respectively
- Used for adjusting the hour/minute and switching LED modes
- Red and Green LEDs are individually wired and behave as follows:
- Red LED:
- Blinks at 1 Hz before 19:00 using `millis()` logic
- After 19:00, represents hour value via PWM intensity
- Green LED:
- Briefly flashes when the minute changes before 19:00
- After 19:00, represents minute value via PWM intensity
- Additional functionality (RGB LED + BTN MODE):
- RGB LED (common cathode) connected to pins D9 / D10 / D11
- Displays one of 7 fixed colours based on `colorIdx` value
- Colour order: Red → Green → Blue → Cyan → Magenta → Yellow → White
- Automatically dims in dark environments (detected via LDR)
- While holding BTN MODE, RGB blinks white at 4 Hz as visual feedback
- BTN MODE (D7, INPUT_PULLUP)
- Short press: advances to the next colour (circular logic using `colorIdx`)
- Long press: enables fast white blinking for visual feedback
- Every action also triggers a short beep (3 kHz, 50 ms) from the buzzer
- Passive Buzzer (D3)
- Emits short beeps on button presses
- Plays a long “gong” at every full hour
- 1 Hz ticking sound every second (disabled between 19:00–23:59)
Software Design
Development environment: Arduino IDE 2.3.7
Libraries:
- Wire.h – establishes I²C communication with the RTC and OLED display
- RTClib.h – used to read and write time from the DS3231 real-time clock module
- Adafruit_GFX.h – provides core graphics functions (fonts, shapes, text positioning) for the OLED
- Adafruit_SSD1306.h – handles display control over I²C for the 128×64 OLED screen
Core functionalities implemented and tested:
- Time tracking with RTC DS3231, updated every second
- OLED display shows time, ambient light (LDR), RGB LED mode and dimMode status
- Dim mode activates automatically when LDR reads below threshold (value < 400), reducing RGB LED brightness
- LED behavior is time-aware:
- Before 19:00: Red LED blinks at 1 Hz; Green LED flashes on minute change
- After 19:00: Red/Green LEDs act as clock hands (PWM based on hour/minute)
- RGB LED cycles through 7 preset colours using PWM; dims automatically at night
- Buzzer generates:
- Short beep on button press (except 19–23 when silent)
- Longer “gong” at the top of each hour
- 1 Hz ticking sound (disabled 19–23)
- All buttons use INPUT_PULLUP and falling-edge detection to avoid bounce
Functions implemented
- void setup() – initializes I/O pins, OLED display, RTC module, and serial communication
- void loop() – non-blocking main loop, checks buttons, updates LEDs and OLED, processes tick events
- void setRGB(uint8_t r, uint8_t g, uint8_t b) – sets the RGB LED to a specific color using PWM
- void beep(uint16_t freq, uint16_t dur) – plays a tone on the buzzer unless time is between 19:00 and 23:59
- uint8_t hourToPWM(uint8_t h) – maps hour (0–23) to a PWM value (0–255) for clock-hand LED behavior
- uint8_t minuteToPWM(uint8_t m) – maps minute (0–59) to PWM value for clock-hand LED behavior
Program logic
- The program uses `millis()` to generate a 1-second tick without blocking the main loop
- At each tick:
- Reads current time from RTC
- Updates system LEDs (red/green) depending on time of day
- Triggers buzzer if needed (heartbeat, hourly gong, button press)
- Refreshes the OLED with current time, light level, color index, and dim mode status
- RGB LED:
- Changes color with each MODE button press
- Blinks white rapidly while MODE is held down (hold-feedback)
- Dims automatically in low light (based on LDR reading)
- LDR:
- Continuously read via `analogRead()`
- Triggers dim mode below threshold (`ldrThreshold = 400`)
- Buttons:
- BTN_H: increments hour on press
- BTN_M: increments minute + beeps
- BTN_MODE: cycles through color presets
How it works
- When powered on, the system initializes all components and retrieves the current time from the DS3231 RTC
- The red LED blinks every second as a heartbeat until 19:00
- After 19:00, the red LED brightness reflects the current hour (PWM), while the green LED reflects the current minute
- The green LED flashes once every new minute before 19:00
- The RGB LED can be set to one of 7 preset colors; it dims automatically at night based on ambient light
- Holding the MODE button causes the RGB LED to blink white rapidly as visual feedback
- The buzzer emits a short beep on button press and a longer “gong” at each full hour, except during the silent hours (19:00–23:59)
- The OLED displays the current time (HH:MM:SS), ambient light level, RGB mode, and whether dim mode is ON/OFF
New features introduced (vs. template)
- Time-dependent LED behavior:
- Classic blinking/flashing before 19:00
- LED “hands” with proportional PWM after 19:00
- Auto-dimming feature using LDR sensor and PWM reduction
- Dynamic buzzer behavior (silent hours implemented in software)
- Multi-mode RGB LED, including a white flashing effect on long-press
- OLED updates every second: Time, light level, current RGB mode, dim status
Features implemented from labs
Lab 3 – PWM, LED breathing & analogRead
- PWM control for RGB LEDs and system LEDs (red/green after 19:00)
- Smooth “breathing” animation effect using PWM on RGB LED
- Light detection using `analogRead()` from an LDR sensor
- Threshold-based logic (`ldrThreshold = 400`) for enabling automatic “dim mode” at night
Lab 4 – millis(), timer-based updates & OLED/RTC integration
- Use of `millis()` for implementing non-blocking 1-second ticks
- Red LED blinking at 1 Hz without using `delay()`
- Real-time clock support via DS3231 and `RTClib`
- Time display updated every second on OLED using `Adafruit_SSD1306`
Lab 5 – tone() and auditory feedback
- Use of `tone()` to play short sounds on button interaction
- Hourly chime (“gong”) at full hour events
- Conditional muting logic: buzzer is disabled between 19:00–23:59 to avoid disturbance
Lab 6 – debouncing, edge detection, and button logic
- All buttons are configured with `INPUT_PULLUP`
- Falling-edge detection using previous state comparison
- Three buttons implemented with distinct actions (hour, minute, mode switching)
- Every interaction triggers a visual and/or auditory feedback
Testing & calibration
- LDR threshold value (`ldrThreshold = 400`) chosen after testing under normal room lighting
- RGB LED tested with dimming and full brightness in varying light conditions
- Buttons debounced and tested for both short press and hold
- Verified correct PWM values for hour (0–23) and minute (0–59) mapping
- Buzzer output silenced reliably in “quiet hours” 19:00–23:59
Software optimizations
- No `delay()` usage – entire loop is non-blocking using `millis()`
- Only updates OLED once per second to avoid flicker
- PWM outputs adjusted only when needed
- All state variables and timing use unsigned types (overflow-safe)
- `tick` flag separates logic from timing checks
Video explanation
- Demo includes:
- Full operation cycle (LED behavior before and after 19:00)
- RGB LED mode change & white blink effect
- LDR dimming effect with covered/uncovered sensor
- Time update via buttons (HOUR, MINUTE)
- Buzzer feedback with conditional silence
- OLED display showing all real-time parameters
Rezultate Obţinute
Care au fost rezultatele obţinute în urma realizării proiectului vostru.
Concluzii
Download
O arhivă (sau mai multe dacă este cazul) cu fişierele obţinute în urma realizării proiectului: surse, scheme, etc. Un fişier README, un ChangeLog, un script de compilare şi copiere automată pe uC crează întotdeauna o impresie bună 
.
.
Fişierele se încarcă pe wiki folosind facilitatea Add Images or other files. Namespace-ul in care se incarca fisierele este de tipul :pm:prj20??:c? sau :pm:prj20??:c?:nume_student (dacă este cazul). Exemplu: Dumitru Alin, 331CC → :pm:prj2009:cc:dumitru_alin.
Journal
06.05.2025 – decided on the project, wrote the description and the hardware materials
11.05.2025 – materials bought, starting on the hardware design
13.05.2025 – tested RTC, OLED, LDR, buzzer and buttons independently
15.05.2025 – implemented LED functionality (blinking, PWM, mode switching)
16.05.2025 – finished integration: all modules tested together
17.05.2025 – added RGB LED support and 7-color switching logic
18.05.2025 – finalized code, added edge detection, PWM breathing, and buzzer feedback
19.05.2025 – created and uploaded schematic + wiring diagram
20.05.2025 – documented project structure and updated project page
Bibliografie/Resurse
Listă cu documente, datasheet-uri, resurse Internet folosite, eventual grupate pe Resurse Software şi Resurse Hardware.
