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The problem
Continuous measurements are the raw material of every monitoring project — weather stations, cold-chain tracking, greenhouse control and lab experiments all start with a reliable log of what happened and when. Dedicated data loggers are expensive, while this project shows the same job can be done with an Arduino Uno, a low-cost sensor and a microSD card. The logger samples a DHT22 temperature-humidity sensor at a configurable interval, appends each reading with an elapsed-time stamp to a CSV file on a FAT32-formatted card, and mirrors the latest values on a 16x2 LCD. Because the file format is plain CSV, the data opens directly in Excel or Python for plotting — no proprietary software, no cloud account, no internet connection at any stage. The build doubles as a platform: the same firmware pattern logs any analog or digital sensor, and the included guide documents swapping the DHT22 for sensors such as the LM35 or BMP280. This is a built-to-order hardware project: the prototype is assembled, wired and tested fresh for your order.
Reads temperature and humidity at each sampling interval (datasheet: +-0.5 C, 2-5% RH, max about 0.5 Hz sampling).
Follow the working sequence
How it works
- On power-up the Arduino initializes the DHT22, the 16x2 LCD and the microSD card over SPI, creating or opening the day's CSV file.
- Every sampling interval (a single configurable constant in the firmware) the DHT22 is read for temperature and humidity.
- The reading is formatted as a CSV row — elapsed time, temperature, humidity — and appended to the card, then flushed.
- The same values are written to the 16x2 LCD for a live on-device readout.
- Logging continues unattended; the Arduino needs no PC or network while it runs.
- The card is removed and read on any computer — the CSV opens directly in Excel or a Python plotting script for the report's graphs.
Tech stack:
- Arduino Uno R3 (ATmega328P)
- MicroSD card module (SPI interface)
- DHT22 temperature & humidity sensor
- 16x2 LCD character display (I2C backpack)
- Arduino IDE with SD library (FAT32 CSV logging)
- microSD card, FAT32 formatted
- 5 V USB power supply or 9 V battery option
| Parameter | Value |
|---|---|
| Controller | Arduino Uno R3, ATmega328P @ 16 MHz |
| Sensor | DHT22: ±0.5 °C, ±2–5 % RH (datasheet values); max ~0.5 Hz sampling |
| Storage | microSD, FAT32; one reading/minute ≈ 1,440 rows/day (≈ 60 KB/day) |
| Display | 16x2 character LCD |
| Sampling interval | 2 s – 60 min, configurable in firmware |
| Timestamp | Elapsed time since power-on (no absolute clock without the optional RTC) |
| Power | 5 V USB; optional 9 V battery for field logging (runtime battery-dependent) |
| Output | Plain CSV, readable in Excel/Python |
Project features
- [Interval data logging] Reads the DHT22 at a configurable interval (design target: 2 seconds to 60 minutes) and appends each reading to a CSV file on the microSD card.
- [Elapsed-time stamping] Every row carries a time stamp derived from the Arduino's clock, so readings stay ordered and plottable without an RTC module.
- [Live LCD readout] A 16x2 character display mirrors the latest temperature and humidity values as they are logged.
- [Plain CSV output] Log files open directly in Excel, Google Sheets or Python — no proprietary software or conversion step.
- [Per-write flushing] Each reading is flushed to the card immediately, so a power cut costs at most the latest sample.
- [Sensor-swappable input] The firmware pattern is documented for swapping the DHT22 with other sensors (LM35, BMP280, LDR) with small code changes.
What is included
- Assembled and tested working prototype (Uno, SD module, DHT22, LCD on breadboard/base)
- Complete firmware source code (logging, LCD, interval configuration)
- Circuit/wiring documentation with connection diagram
- Component list with sourcing notes
- Sensor-swap guide (LM35, BMP280 and other sensors)
- Sample CSV log and a plotting starter script
- Project report PDF (background, methodology, sample logged data, analysis)
- PPT presentation for final review
- Viva Q&A preparation document (SPI, FAT32, DHT22 protocol, sampling theory)
Advantages
- PC-free logging: the Arduino reads the DHT22 at a configurable interval and appends every reading with an elapsed-time stamp to a CSV on microSD, with no PC or internet needed during logging.
- Excel-ready output: plain CSV log files open directly in Excel, Google Sheets or Python, with no proprietary software or conversion step.
- Live LCD mirror: a 16x2 character display shows the latest temperature and humidity values as they are logged.
- Data-safe writes: each reading is flushed to the card immediately, so a power cut costs at most the latest sample.
- Configurable sampling: the sampling interval is adjustable in firmware, with a design target from 2 seconds to 60 minutes.
- Sensor-swappable design: the firmware pattern is documented for swapping the DHT22 with other sensors (LM35, BMP280, LDR) with small code changes.
Disadvantages
- The DHT22's datasheet accuracy is plus/minus 0.5 degrees C and 2-5% RH, and it cannot sample faster than about once every 2 seconds: finer or faster sensing needs a different sensor.
- Timestamps are elapsed time since power-on: there is no absolute date or time unless the optional DS3231 RTC module is added (available as a customization).
- Cheap or counterfeit microSD cards can corrupt data: the guide recommends tested card brands and FAT32 formatting.
- A power cut during the brief write window can corrupt the file being written: per-write flushing limits loss to the latest sample but not to zero.
- The prototype is a bench/room logger, not a weatherproof field unit: outdoor use needs an enclosure (customization).
Limitations & prerequisites
- The DHT22's datasheet accuracy is ±0.5 °C and ±2–5 % RH, and it cannot sample faster than about once every 2 seconds — finer or faster sensing needs a different sensor.
- Timestamps are elapsed time since power-on; there is no absolute date/time unless the optional DS3231 RTC module is added (available as a customization).
- Cheap or counterfeit microSD cards can corrupt data; the guide recommends tested card brands and FAT32 formatting.
- A power cut during the brief write window can corrupt the file being written; per-write flushing limits loss to the latest sample but not to zero.
- The prototype is a bench/room logger, not a weatherproof field unit — outdoor use needs an enclosure (customization).
Frequently Asked Questions
Which controller is used?
An Arduino Uno R3 (ATmega328P). The firmware is plain Arduino C++ using the SD library — easy to read and explain in a viva.
Can I log a different sensor?
Yes — the firmware's read-format-write pattern is sensor-agnostic, and the included sensor-swap guide documents moving to the LM35, BMP280 or an LDR with small code changes.
Does it need Wi-Fi or internet?
No. Logging is fully offline to the microSD card; the card is read on a PC afterwards. A Wi-Fi upload variant (ESP32) is possible as a customization.
What power supply is needed?
Any 5 V USB source for bench logging; a 9 V battery can power short field runs, with runtime depending on the battery and sampling interval.
What are the main limitations?
DHT22 accuracy and 2-second minimum interval, elapsed-time (not absolute) timestamps without the optional RTC, and SD-card quality dependence. Details are in Limitations & Prerequisites above.
Is this project suitable for a final-year project?
Yes — for Electronics, IoT and Instrumentation programs. It demonstrates SPI communication, FAT32 file handling, sensor interfacing and real data analysis from the student's own logged data. Suitable for B.E./B.Tech final-year projects in Electronics, IoT and Instrumentation Engineering.
Components & software requirements
- Arduino Uno R3 (ATmega328P)
- MicroSD card module (SPI interface)
- DHT22 temperature & humidity sensor
- 16x2 LCD character display (I2C backpack)
- Arduino IDE with SD library (FAT32 CSV logging)
- microSD card, FAT32 formatted
- 5 V USB power supply or 9 V battery option
Delivery information
Built-to-order project. Delivery timeline is shared after order confirmation based on current queue.
Support terms
Complete documentation, setup guide, and viva preparation included. Support for setup and explanation provided.
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