Low voltage indicator

Hi. I just got my TL431 but it's not doing as well as i had hoped.

What i need to achieve is a low voltage warning at 2.5Vdc
It's an amplifier i have made that is driven on 3Vdc (2x AA@1,5V)
and it's doing well. one week without turning it off and i've lost 0.14V

So how the heck am i to make this work? a led to turn on at 2.5V left...

What i need to achieve is a low voltage warning at 2.5Vdc

So what circuit are you trying to do this?
I would have thought that you take the reference voltage chip and put it into a voltage comparator to fire when the input voltage drops lower.
However you have not said what circuit you are using the TL431 in.

whoops xD Sorry

It's should be mounted in between the Amp and the Battery pack.

Also i'm not using my arduino at all at this stage of the project (might be usefull to know)

OK let's rewind.
What exactly are you asking here?
Do you want someone to design a circuit for you?
Or do you have a circuit?
The chip by itself is only a very small part of the system.
What do you want to happen when the voltage drops below this threshold?

Im sorry for lack of information xD

No i have a circuit. It is the very same as sparkfuns "uh oh kit"
But no matter what i do the only thing that happens is that the led is on all the time. But slightly dimmed when configurated to aprox 2.5v at tp1 of said circuit. What it SHOULD do is to light the led when voltage hit and drops below 2.5v

It could be my 10k pot thats faulty. But the only replacements i have at hand at the moment are a 75k pot and a 1M pot.

Dont want anyone to design it for me. Just some help with what i may be doing wrongly... Also i find said circuit kinda consfusing and thats rare :-/

What colour is your LED?
The schematic says that it should have a forward voltage drop of more than 2.5V. That rules out red and most new forms of white.
An old blue one might work.

Also i find said circuit kinda consfusing and thats rare :-/

Me too, it is a most odd thing.
Measure the voltage you are getting on your wiper, does it adjust from 0 right up to the supply? If it does your pot and wiring is fine.

What it SHOULD do is to light the led when voltage hit and drops below 2.5v

I don't think so. If the voltage is below 2.5V and that is the forward volts drop of the LED then by definition the LED can not come on.

i have tried a Red, a green and a UV

and for the pot... it's odd... when i measure the resistance i get from 384 Ohm to 10k, nothing below 384... crap...

and since the 431 has a 2.5v Reference i cannot go below that right? Hence why the led voltage drop has to be higher?
Or is it all due to the configurations of the resistors?

found a Green led now while writing this, measured with diode setting on multimeter it said 1.9 and then straght to 1. (out of range) maybe it'll work?

and for the pot... it's odd... when i measure the resistance i get from 384 Ohm to 10k, nothing below 384.

Have you measured the resistance between the two ends of the pot?
You need to measure the voltage on the wiper when it is in circuit.

measured with diode setting on multimeter it said 1.9

That doesn't usually mean much.

and since the 431 has a 2.5v Reference i cannot go below that right?

Yes

Hmm... haven't measured the voltage on the wiper :confused: Will do tomorrow. (How come i fail at these simple tasks but manage to hook a NTC to the arduino and calculate to be accurate to 0,01 Degree Celsius? (Off Topic))

And since i cannot go below the reference... Is there a way for this? For a Led to turn on when Voltage hits and drops below 2.5V?

Example: A second circuit to be given the signal from the 431 that the Voltage is at 2.5 and below? Like a FET and a coincell hooked to a LED? (Bad idea? It's getting late xD shouldn't think this much before bed)

EDIT:

Solved it!

a NPN and a Zener plus two 100 Ohm Resistors. Works like a charm ^^