Arduino ARef - TLV431

Hi everyone,
Today I try to use Aref using TLV 431 VKA = VREF cicuit, with 10uF to get
a constant low voltage of 1.24 Volt for Arudino's ADC Reference Voltage.

http://www.datasheetarchive.com/pdf-datasheets/Datasheets-23/DSA-456906.html

The Problem that I face is that this voltage is not stable, it is up and down
slowly...(about 1 min--> 0.01 Volt).
What I need is a really low stable voltage. Any help, suggestion or hint?
Thank you. :slight_smile:

The TLV431 is a 2.5V device. It's not going to give you 1.24V (I guess you could use a voltage divider but then you'll lose some precision).

Your variation of 10mV is not that surprising. This part has variations in that range with temperature and time (e.g., 2.7mV/V variation with supply voltage, 30mV variation with temperature). You also have to have a very good measuring instrument to be able to say the voltage is varying 10mV.

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Well, if you see in the usual application there is an example of application to make it 1.24 V.
What I get now is a stable voltage of 1.239 V , so that is ok for me.

2.7mV/V using 1.24 V power supply it should be only 0.003348 V ( 3.348mV) variation.

My trouble now is not about the variaton, but the ringing up and down.
It is alright, if it will become 1.3 V but I need it to be stable.
For now the ringing up and down is from 1.250 - 1.310 Volt. (Slowly change up and down).

This morning I check arduino by sticking a copper in aref pin and GND pin.
Then measure the Voltage, what i get is a voltage ringing from 4.050 -4.761 gradually change. Then the problem is inside arduino. Is there something I could do? Thank you.

This is interesting, because it suggests your Arduino is not getting 5V. Can you see what the 5V supply is? Does it vary too?

Either you have the A/D conversions set up for a 5V reference, in which case 5V should appear at AREF, or AREF is floating and it could very well vary as you measured.

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Thank you RuggedCircuits, now I know my problem.
My problem is in the software, I haven't set the analogReference(type).
So critical thing that forgotten. Sorry for the trouble. Thanks.