What it shows
An Arduino with a DS3231 clock writes a time-stamped line of light, temperature and humidity readings to a micro SD card every ten minutes. Opened in a spreadsheet, the file shows how conditions inside a covered bed differ from outside over several days.
The science
The DS3231 keeps time with a temperature-compensated crystal and a coin cell, so every record carries a real date and time even after a reset. The SD module talks over SPI, and the SD library appends text lines to a CSV file. Each line has the clock time, the LDR divider value, and the DHT11 values. Reading every ten minutes gives 144 points a day, enough to show the daily cycle. A spreadsheet chart of the data makes the heat trapping of the polyhouse visible.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An Arduino Uno clone and USB cable
- A micro SD card module and a card of 2 to 32 GB
- A DS3231 real-time clock module
- A DHT11 module and an LDR with a 10 kΩ resistor
- A 5 V power bank or a 5 V USB mobile charger (a 9 V battery lasts only a few hours)
- A plastic box to keep the electronics dry
- A sheet of clear plastic and sticks for a mini polyhouse
Safety
For this project: USB power only, from a power bank or a certified mobile charger. Keep the box sealed with the sensors outside through small holes.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Wire the SD module: CS to pin 10, MOSI 11, MISO 12, SCK 13, VCC 5 V, GND. Format the card as FAT32.
Wire the DS3231 on A4 and A5 and set its time once with the library example that uses the compile time.
Wire the DHT11 to pin 2 and the LDR divider to A0.
Write a sketch that on start opens log.csv and writes a header line if the file is new.
Every ten minutes read all sensors and append a line: date, time, light, temperature, humidity.
Flush and close the file after every write so a lost battery does not corrupt the card.
Blink the built-in LED on each write so you know it is working without a computer.
Place the box with the sensors inside the mini polyhouse, and run a second set-up outside if you have the parts, for three days.
Open the CSV in a spreadsheet and plot temperature and light against time for the report.
What you should see
A CSV file with several hundred time-stamped rows; the chart shows the polyhouse running a few degrees warmer by day and holding humidity at night.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why use a real-time clock instead of millis()?
millis() restarts at zero on reset and does not know the date; the RTC keeps real time on its coin cell.
02What is CSV?
Comma separated values, a plain text table that any spreadsheet can open.
03Why close the file after each write?
Data sits in a buffer until the file is closed or flushed; a power loss before that loses it.
04Why does the polyhouse stay warm at night?
The cover slows the loss of warm air and reduces radiation to the sky, so heat gathered by day is kept longer.
Take it further
Add a soil probe and show the link between day heat and soil drying.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Robotics
Arduino and Coding for Robots Study Book
The complete study notes, practice questions and glossary for Arduino and Coding for Robots
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