AnalogRef Pin issues (or missunderstanding?)

[lost_memories]

Hello,

I'm looking to increase the resolution of my Analog-In pin reading for low voltage readings. Because the thing I try to measure cannot handle a lot of Power, I have to use a rather large resistor in my voltage divider to keep voltage and current to a minimum. I try to stay in the realm of 0.1-0.3V of measuring voltage range.
Using the regular resolution of 5V/1024 is way too inaccurate for what I'm doing, sadly.
I tried using the ARef pin with a supposed low voltage, however it seems like I short my setup whenever I try to connect it to sth. (I get 1023 as Pin reading value).

The way I tried to get a low ref voltage is via using the 5V pin and ground, setting up another voltage divider and feeding the signal in between those two resistors into the Aref pin.
It worked fine on Tinker Cad simulation before I built it, so I don't really know what is happening or why it seems so short it when I built it IRL.
Am I missing something on what the Aref actually does? I'm quite new to all this.

[LarryD]

• Did you try the 1.1v internal reference (Uno) ?

• There is also the option of adding an external amplifier, ex X10 (LMV321)

• You can get an external A/D too.

[jremington]

For Arduino Uno R3, Mega, Classic Nano study this excellent tutorial:

Gammon Forum : Electronics : Microprocessors : ADC conversion on the Arduino...

[lost_memories]

I tested arround with the 1.1V Internal Reference, but sadly it still wasn't enough. I try to limit the resolution to a max of 0.5V.
I will look into the amplifier solution, but since I'm doing this for the first time, chances are slim that I'll get it right.

[kolaha]

@lost_memories

I have to use a rather large resistor in my voltage divider to keep voltage and current to a minimum

show schematic

[Wawa]

@lost_memories

I try to limit the resolution to a max of 0.5V.

Minimum recommended Aref voltage for an Uno R3 is 1volt.

The ADS1115 can measure 0.256volt with a 15-bit resolution, but internal impedance might be a problem for your setup.
Leo..

[oldcurmudgeon]

For a low level signal you need an amplifier before the ADC. The UNO Vref minimum is 1V, so you will have trouble getting the resolution you want by adjusting Vref.

[hammy]

It would be useful to know your transducer type - there maybe alternatives .
As said using the internal reference (1.1v) gives a voltage resolution of around 0.001 volt ( 1mV)
Better than that you are looking at amplification and careful design and layout to get accuracy and resolution.
If you switch your device On/Off from a digital output , then you can save power and avoid high value resistors .

[johnerrington]

@lost_memories

The way I tried to get a low ref voltage is via using the 5V pin and ground, setting up another voltage divider and feeding the signal in between those two resistors into the Aref pin.

How to make a schematic you can post.

When you submit a question on the forum you will usually need to add a schematic (circuit diagram). The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy. Having created the image all you need to do is : Save the image somewhere convenient - maybe your desktop Start your post, and place the cursor (insertion point) where you want the image to be shown; [upload image to forum] 3: click th…

Playing with the Aref pin is a recipe for disaster. Also the ADC is unlikely to give better resolution with a lower Aref.

Its very easy to make an amplifier to give a better signal to your ADC.

Using Operational Amplifiers in your Arduino project

Introduction: Using Op Amps to measure signals with an Arduino Who is this tutorial for? Well, not "newbies" or anyone happy to just connect together modules. If you have a LITTLE knowledge of electronics, have perhaps used a transistor or a FET to extend the output capability of an arduino, and want to learn about ways to handle different Analog inputs, than read on! What will you need? All you will need to carry out a few simple experiments is a breadboard, a couple of (very inexpensive) …

Alternatively you can use an external adc such as the ADS1115 to read the voltage directly.

[b707]

@lost_memories

The way I tried to get a low ref voltage is via using the 5V pin and ground, setting up another voltage divider and feeding the signal in between those two resistors into the Aref pin.

By supplying voltage to the AREF from the power supply through a divider, you are unlikely to increase the accuracy - more likely, that you will lose it. To the inaccuracies of the ADC itself will be added the inaccuracy of the divider resistances and instability of the supply voltage.

If you want to work with aref, the first thing you need is a stabilized voltage source

[jim-p]

@lost_memories

I have to use a rather large resistor in my voltage divider to keep voltage and current to a minimum.

Limiting the current makes sense but keeping the voltage to a minimum does not.
How much voltage can this "thing" output?
If it can output more than 5V, then why limit the voltage?

[GolamMostafa]

@lost_memories

I try to stay in the realm of 0.1-0.3V of measuring voltage range.

If you are using Arduino UNO and AREF-pin to feed external voltage at the V_REF pin of the ADC, then the minum voltage that you can apply on AREF-pin is 1.1V (Fig-1). So, it is better to use the most stable internal 1.1V as reference.

Figure-1:

If you want higher resolution, you go with the following 16-bit external ADC Breakout Board (Fig-2) as others have advocated.

Figure-2:

[Delta_G]

@lost_memories

however it seems like I short my setup whenever I try to connect it to sth.

What is an sth?

[alto777]

something

a7

[Koepel]

@alto777 You had me fooled.
For everyone else who didn't get it: sth is an abbreviation for something.

[GolamMostafa]

@Koepel

sth is an abbreviation for something.

Abbreviation is a noun word, which is taken as a short for a relatively big title. Here, something is just a word.

[b707]

@GolamMostafa

something is just a word.

... and sth is its abbreviation.