A cyclic timer module based on Arduino and DS3231 RTC, featuring dual opto-isolated relay outputs for time-based automation.

📌 Overview

This project implements a reliable and flexible cyclic timer system using an Arduino and a DS3231 real-time clock (RTC). It is designed for applications requiring precise periodic control with configurable timing parameters.

The system operates in cyclic intervals, activating outputs based on time windows and pre-trigger conditions.

✨ Features Dual relay outputs (opto-isolated) High-accuracy timing using DS3231 RTC Configurable working hours (start / end time) Cyclic operation with adjustable interval Adjustable ON time for main load (Relay 1) Pre-trigger output (Relay 2) before cycle end Simple and efficient logic (no complex timers required) Industrial-style behavior 🧠 Operating Modes

This project includes two different firmware modes:

1. RTC Setup Mode

This mode allows setting the date and time of the RTC via Serial communication.

Input format:

day,month,year,hour,minute,second

Example:

17,3,2026,19,25,00 The RTC updates automatically when valid data is received. 2. Operation Mode

This is the main working mode of the system.

Executes cyclic timing logic Controls both relays automatically Uses RTC as time reference No Serial interaction required

⚠️ Important: The RTC must be configured before uploading the operation firmware.

⚙️ Configuration Parameters

The system behavior can be easily adjusted in the code:

horaInicio → System start hour (24h format) horaFin → System stop hour tiempoEspera → Cycle interval (minutes) tiempoCarga → Relay 1 ON time (minutes) tiempoHumo → Relay 2 activation time before shutdown (seconds)

🚀 Usage Upload the RTC Setup Mode firmware Open Serial Monitor Send current date and time Upload the Operation Mode firmware System runs automatically

🔌 Hardware Arduino Nano DS3231 RTC module Opto-isolated relay driver Transistor (2N2222A) Flyback diode (1N4148 or 1N4007)

⚡ Circuit Notes Relays are driven using a transistor (2N2222A) Optocoupler provides electrical isolation Flyback diode protects against voltage spikes Pull-down resistor ensures stable OFF state 📷 Project Images

⚠️ Important Notes RTC keeps time using backup battery No need to reset time unless battery is removed Ensure correct time before operation Verify relay ratings for your load (especially AC)

📦 Future Improvements Serial configuration in operation mode EEPROM parameter storage LCD/OLED interface Multiple independent channels millis() based control (non-blocking) 📜 License

This project is licensed under the MIT License.

👨‍💻 Author

Developed by Cristian E. Guerrero

⭐ Contributions

Feel free to fork, improve, and contribute to this project!