I’m having an issue with a project that uses the Atmel atmega328 @ 3.3volts. Seems if both the ADC and the Usart are active at the same time (IE: using Serial.print() followed by AnalogRead()) the board would reset. I think that the Serial.print() function is interrupt driven, so all it does is load a buffer and enable interrupts. So depending on the baud rate by the time you execute the AnalogRead() the ADC is running while the usart is transmitting in the background. Either the processor has an issue at 3.3volts with the ADC, or my board is going into brownout due to a problem with the 3.3volt regulator I’m using (how much does running both the ADC and Usart increase the processor power draw?). Has anybody using a pro mini at 3.3v seen this before? (I don’t see this on a UNO running at 5v).
You are using the stock regulator correct?
What pin are you reading for the analog?
What is connected to the UART pins?
What is connected to the analog pin(s)?
Agree with Joe. You need to provide a schematic (at least a partial one) so we can see how you’ve connected everything.