Bare Arduino Uno (Atmega328) with SX1278 LoRa

I am doing a LoRa based project based on the Atmega328, I did my initial test using the Arduino uno & LoRa SX1278 module and everything works fine. I then moved tge project to a bare minimum arduino circuit (project is battery powered and want to save on battery power), the arduno starts up but the LoRa module cannot send or recieve anymore and when i check i see that the LoRa module keeps pulling its input voltage to 4.2V from the 3.3v on its input.

Does anyone know why this is happening?

The SX1278 is a 3.3V device and you should only directly connect it to a 3.3V Arduino.

If your Arduino is a 5V device then you need to use logic level conversion stuff to connect the SX1278.

It would help the forum if you had provided details of the Atmega328 you are using and how it is powered and connected to the SX1278.