Soil Moisture Logger with RTC & SD Card

Author: Bocaletto Luca

Files

• README.md
• SoilMoistureLogger.ino

1. Concept

An autonomous data‐logger that measures soil moisture with a capacitive sensor at regular intervals (and on‐demand via a push‐button), timestamps each reading using a DS3231 RTC, and appends entries to a CSV file on a microSD card. Perfect for greenhouse monitoring or unattended field deployments.

2. Bill of Materials

• Arduino Uno (or Nano)
• Capacitive soil moisture sensor (e.g. Chirp or SEN0193)
• DS3231 RTC module
• Micro SD card module + 4 GB (or larger) microSD card
• Push‐button + 10 kΩ pull‐down resistor
• Status LED (optional) + 220 Ω resistor
• Breadboard & jumper wires
• 5 V power supply (USB or battery pack)

3. Wiring Diagram

Capacitive Sensor        Arduino Uno
┌─────────────┐          ┌─────────┐
│ VCC ───► 5V │          │         │
│ GND ───► GND│          │         │
│ AOUT ──► A0 │          │         │
└─────────────┘          └─────────┘

DS3231 RTC (I2C)
┌─────────────┐
│ SDA ───► A4 │
│ SCL ───► A5 │
│ VCC ───► 5V │
│ GND ───► GND│
└─────────────┘

SD Card Module (SPI)
┌─────────────┐          ┌──────────┐
│ CS  ───► D10│          │         │
│ MOSI ─► D11│          │         │
│ MISO ─► D12│          │         │
│ SCK  ─► D13│          │         │
│ VCC ───► 5V │          │         │
│ GND ───► GND│          │         │
└─────────────┘          └──────────┘

Push‐button             Arduino Uno
┌─────────┐             ┌─────────┐
│ one leg─┬─► D2        │         │
│ other ──┴─► GND       │         │
└─────────┘             └─────────┘
(Use 10 kΩ from D2 to GND for pull‐down)

Optional LED
┌─────────┐             ┌─────────┐
│ Anode ─┬─► D8         │         │
│ Cath. ─┴─► GND        │         │
└─────────┘             └─────────┘
(Include 220 Ω resistor in series)

4. Software Setup

1. Install Arduino IDE (≥1.8.x).
2. In Library Manager, install:
   • RTClib by Adafruit
   • SD (built-in)
3. Create folder SoilMoistureLogger and save both files.
4. Open SoilMoistureLogger.ino in the IDE.
5. The logger writes soil_log.csv on the SD root with columns: timestamp,moisture 2025-06-20 14:00:00,412
6. Automatic readings every 10 minutes; press the button to force a manual reading.
7. LED blinks once on each log.

Say continua when you’re ready for project #9!

6. Select Arduino Uno and the correct COM port.

5. Usage

1. Format your SD card as FAT32.
2. Ensure RTC.adjust(DateTime(F(__DATE__), F(__TIME__))); is commented out after initial time‐set.
3. Upload sketch.
4. Open Serial Monitor at 9600 baud to follow status messages.
5. The logger writes soil_log.csv on the SD root with columns: