Скачать или смотреть 6 ARDUINO ANALOG analogReference

analogReference() function is not necessary for majority of the sensors you will see but it is a good idea to know when to use it.

Recall that the analogRead() function will read in a voltage value between 0-5V and convert that to 0-1023 using the ADC (analog-to-digital converter) hardware that is inside the Arduino processor. Now, what if the sensor you picked used +3.3V instead of +5V?
There are two possible answers to this question:
1) Nothing wire the sensor with a 3.3V power, the readings will be between 0-3.3V so when you read it from the analog port, the values will go from 0-676 instead of 0-1023.
2) IF however you want to use the full 0-1023 range, we could use analogReference() function. analogReference() function can be used to map the 0-1023 values to the 0-3.3V range. To do this, 3.3V must also be connected to the AREF pin (just above Digital pin 13). analogReference(EXTERNAL); should then be added to the setup() portion of the code.