I made a data logger for temperature and humidity.
- Board: Arduino Pro Mini
- Sensor: BME280
- Display: LCD 4×20 with I2C expander
- Real Time Clock: DS3231 module
- Logging: Average, min and maks of temperature and humidity
- Capacity: 1 year!
Data storage: Every day 6 values are stored:
- Average temperature
- Min temperature
- Max temperature
- Average humidity
- Min humidity
- Max humidity
All values are stored with one decimal, and so every day takes up 12 byte of storage.
The Arduino Pro Mini has 1024 byte of EEPROM storage.
On the DS3231 module there is a EEPROM 24C32 with 4096 byte storage. So this is enough to store one full year.
January to November are stored in the 24C32 (12 x 11 x 31 = 4092 byte) and December is stored in the Pro Mini (12 x 31 = 372 byte.
There is a serial interface menu, so the values can be extracted with a USB cable to the Arduino and the serial monitor on the PC.
The Pro Mini has no direct USB interface, so I use a FTI cable with built in TTl to RS232 converter.