# analogReference(EXTERNAL) **URL:** \ **Category:** Sensors\ **Created:** [May 13, 2023, 3:15pm UTC](https://forum.arduino.cc/t/analogreference-external/1126566 "2023-05-13T15:15:40Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![SliferUria](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/sliferuria/32/1116089_2.png) [@SliferUria](https://forum.arduino.cc/u/SliferUria)\ **Post date:** [May 13, 2023, 3:15pm UTC](https://forum.arduino.cc/t/analogreference-external/1126566/1 "2023-05-13T15:15:41Z")
Hi, I want 1.8 [V] as reference for analog input ports. I've connected 2 resistences (15 [kOmh] and 18 [kOmh]) to 3.3 [V] supply of my Arduino UNO. As expected there are 1.8 [V] on R2. ![Da cancellare](https://europe1.discourse-cdn.com/arduino/original/4X/8/d/2/8d22d063663e1fb3ec694f81badc8f5cdeb546d3.jpeg) But if i connect Aref as in the Image the voltage on R2 drop to 1.2 [V]. Why this happen? Does the Aref assorb so much current? Why the voltage is so low? ---
**Author:** ![gilshultz](https://avatars.discourse-cdn.com/v4/letter/g/67e7ee/32.png) [@gilshultz](https://forum.arduino.cc/u/gilshultz)\ **Post date:** [May 13, 2023, 3:19pm UTC](https://forum.arduino.cc/t/analogreference-external/1126566/2 "2023-05-13T15:19:22Z")
I will take a SWAG and say you need to program it for an external reference. I do not remember the details but there is a multiplexer in the processor that selects the reference voltage source, and I believe by default the Arduino is set to use an internal reference. ---
**Author:** ![Koepel](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/koepel/32/637546_2.png) [@Koepel](https://forum.arduino.cc/u/Koepel)\ **Post date:** [May 13, 2023, 3:29pm UTC](https://forum.arduino.cc/t/analogreference-external/1126566/3 "2023-05-13T15:29:28Z")
The AREF has an internal resistor of 32 kΩ to GND. Manufacturer's page of the ATmega328P: [https://www.microchip.com/en-us/product/ATmega328P](https://www.microchip.com/en-us/product/ATmega328P) The [datasheet](https://ww1.microchip.com/downloads/aemDocuments/documents/MCU08/ProductDocuments/DataSheets/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061B.pdf) is the second document (the first is automotive). Page 319, Section 29.8, Table 29-15: ![afbeelding](https://europe1.discourse-cdn.com/arduino/original/4X/d/6/6/d668471b3ffceb9f618fed516975a907ffd1aaf3.png) ---
**Author:** ![hammy](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/hammy/32/238813_2.png) [@hammy](https://forum.arduino.cc/u/hammy)\ **Post date:** [May 13, 2023, 6:48pm UTC](https://forum.arduino.cc/t/analogreference-external/1126566/4 "2023-05-13T18:48:55Z")
Just use the internal 1.1volt reference , it is nice and stable and easy to use! Send your analog measurement via a potential divider , so 1.1 corresponds to the maximum input you make . This method also gives you better protection against over voltage too ! any voltmeter type circuit will need calibrating . ---
**Author:** ![Wawa](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/wawa/32/1211303_2.png) [@Wawa](https://forum.arduino.cc/u/Wawa)\ **Post date:** [May 13, 2023, 9:17pm UTC](https://forum.arduino.cc/t/analogreference-external/1126566/5 "2023-05-13T21:17:11Z")
> [@Koepel](#): > > The AREF has an internal resistor of 32 kΩ to GND. +1 Meaning you already have one resistor of the voltage divider, so you only need to calculate the value of a single resistor between the 3.3volt pin and the Aref pin. Don't use a resistor to ground. I calculate 27k. Leo.. ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [November 9, 2023, 9:18pm UTC](https://forum.arduino.cc/t/analogreference-external/1126566/6 "2023-11-09T21:18:03Z")
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