My project is a simple timestamp logger. I'm using a FRDM-KL25Z with a DS3231 I2C clock module, and 2 buttons with 22K pullups. I assume I have a Rev-D board since there is no provision on board for a 5v regulator and associated caps.
It works well when connected to my PC using the KL25Z-USB connector, but not when using the other supply options. I have tried regulated 5v on VIN and regulated 3.3 v on the 3.3v pin. The program does not work with either. Both behave the same as when I use the OpenSDA connector ( which I know does not allow the program to run). I have not tried attaching a coin cell yet.
How do I power the project with a battery?