## Project notes 2022-10-28 (Build a voltage logger!)

I need a data logger to track charge- and discharge characteristics during the project, and I just realized I don't own one. So let's build one quickly and write some code in Arduino IDE. We need these parts:

- ESP8266 D1-mini to read the analog voltage (DAC) and be the brain of the breadboard logger.
- SD card reader. Many SPI displays have these as standard. I found that I had one, but only with the old large SD card format.
- I need some display to monitor the logger process.

3S-lithium is commonly charged up to 12.6V (3 x 4.2V) and the microcontroller ADC only handles up to 3.3V. For cells in parallel, the maximum voltage is 4.2V, and this is not optimal for the ADC available 10-bits. So the simple voltage divider was rapidly born. With a jumper, it can reduce the input voltage to either 75% or 25%. That should cover our needs. Purchase these small and very useful mini-boards at Tindie if you are curious.

I will soon set up a GitHub software repository for the project and all other helper programs that may be added, like this logger code.