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.
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.
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
The datasheet is the second document (the first is automotive).
Page 319, Section 29.8, Table 29-15:
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 .
+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..
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