This page covers the simple version of the project. The simple version adds an additional persistent RAM chip to the device to allow more records and more precise records.

See the following wiring diagram, it included the RAM module connected over the I²C bus to the microcontroller.

To build the hardware, follow the instructions on the “Build the Hardware (Minimal)” page, except you add the additional board the with the persistent RAM.

The FRAM Module

For my project I use the Adafruit I2C Non-Volatile FRAM Breakout with 32KByte. You may wonder why I use FRAM for the project, because it is expensive compared to flash RAM.

• FRAM requires less power to write.
• FRAM can be written byte by byte. It is not necessary to ease a whole page before writing a byte.
• Each byte in the FRAM can be read/written 10’000’000’000’000 times.

There are many alternatives you can use:

• Use a SD card adapter and write the data to the SD card.
  This is probably not a good solution, because writing data to an SD card needs a lot of power. If you plan to log data over a long time period, you should consider other solutions.
• Use a flash chip, like the following ones:
  • The W25Q80BV – 1MB Flash.
  • The AT26DF081A – 1MB Flash.

Continue reading: Build the Software