ESP32 Cronjob Micro-Server

🎯 Objectives

• A self-contained cronjob server on ESP32.
• Web UI for job management.
• Store jobs + logs on SD card.
• Execute scheduled HTTP requests.
• Include cooling fan control + temperature monitoring.
• Provide built-in UPS system (direct mains with automatic battery backup).

🏗️ System Architecture

Hardware Blocks

• ESP32: main controller (Wi-Fi, task scheduling, HTTP client/server).
• SD Card: persistent storage (jobs.json, logs).
• Micro SD Card Module: Card Reader Module Adapter SPI (6 pins).
• Fan + Temp Sensor: cooling system (GPIO + MOSFET + BME280 sensor).
• Power System (UPS-style):

• 5V Adapter → TP4056 (charging) → Li-ion battery → Step-down (3.3V for ESP32).

• ESP32 always runs from adapter (mains).

• When mains disconnects → auto-switch to Li-ion battery.

• ESP32 monitors battery voltage via ADC.

Software Blocks

• Web Server: UI + REST API endpoints.
• Scheduler: Cron parser + FreeRTOS tasks.
• Job Executor: HTTP client with retry logic.
• Storage Manager: JSON read/write to SD.
• Fan Control: based on temperature threshold.
• Power Monitor: mains/battery status, low battery alerts.

⚙️ Workflow

1. Boot-up

• Initialize SD, Wi-Fi, RTC/NTP sync.
• Load jobs.json into memory.
• Start Web UI + API server.
• Launch background tasks (scheduler, monitoring).

2. Adding a Job (via Web UI)

• User submits form (URL, method, cron expression, retries, headers, etc.).
• ESP32 stores job in memory + updates jobs.json.

3. Scheduler Operation

• Cron parser checks system time vs. job rules.
• When a match occurs → dispatch task to executor.

4. Job Execution

• Perform HTTP request (GET/POST).
• Retry on failure (configurable).
• Log results (errors.log on SD).

5. Cooling System

• Read temperature (BME280).
• Adjust fan speed via PWM based on temperature.

6. Power Monitoring (UPS)

• ESP32 normally powered from mains (5V adapter).
• On mains loss → seamless switch to Li-ion battery.
• Monitor battery voltage via ADC.
• On low battery → log + optional alert (HTTP callback).

🚀 Implementation Plan

Phase 1: Core Setup

• Setup ESP32 development (Arduino/ESP-IDF).
• Integrate SD card (read/write JSON).
• Implement Wi-Fi + NTP sync.
• Basic web server (serve HTML/JS + simple API).

Phase 2: Job Management

• Define job format (JSON schema).
• Build Web UI for job creation/editing.
• Implement scheduler (cron parser).
• Job execution via HTTP client.
• Logging system (to SD).

Phase 3: Monitoring & Cooling

• Integrate BME280 temperature sensor.
• Fan control logic (PWM + MOSFET).
• Temperature logs.

Phase 4: Power System (UPS)

• Setup TP4056 charging + battery pack.
• Configure seamless mains-to-battery switching.
• ADC-based voltage monitoring.
• Alerts/logging on low battery.

Phase 5: Polish

• UI improvements (job list, logs viewer).
• OTA firmware update support.
• Optional: WebSocket live logs.
• Security (auth for UI/API, HTTPS if possible).

📂 File Structure (Proposed)

src/
├── sketch.ino (main file)
├── scheduler.h
├── http_client.h
├── storage.h
├── fan_control.h
└── power_monitor.h