Max voltage on analog pins when using 1.1 Ref

Projects General Guidance
1

I need to measure 5VDC and 1mVDC. I can use analogReference(DEFAULT) to measure the 5VDC and then use analogReference(INTERNAL) to measure the 1mVDC, but when I switch to (INTERNAL) the 5V is still applied to a pin. Is that a problem or can no pin have more than 1.1V when (INTERNAL) is used just like no pin can have higher than 5V when (DEFAULT) is used??

Thanks for your help!

Doug

2

The definitive answer is in the 328 datasheet,

but if I am correct the max voltage is still 5V , but all voltages between 1.1 and 5.0 will map on 1023

3

update from datasheet

24.5.2 ADC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range for the ADC. Single
ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as
either AVCC, internal 1.1V reference, or external AREF pin.

4

Thanks Rob for pointing me in the right direction!!

Doug