How do I wire either of these components so that they output a stable 2.5v to use as the reference on the arduino/Atmega328?
It is required that I use external vRef and it has to be one of these components.
How accurate do you have to be.
There are other inbuild ref voltages.
Leo..
Wawa:
How accurate do you have to be.
There are other inbuild ref voltages.
http://www.arduino.cc/en/Reference/AnalogReference?from=Reference.AREF
Leo..
Just enough where I can sort of rely on it.
I am aware of the internal AREF but I NEED to use one of these external components and the thing is that I don't know how to wire them.
I was under the impression that I connected anode and cathode to the component and the 3rd pin will output a 2.5v but it does not and it gets hot. Can you tell me how to wire them? I have updated the original post with the component parts. Thanks!
+5 to resistor end, other end to pin2, pin 3 to Gnd.
Pin2 is the 2.5V reference.
https://www.fairchildsemi.com/datasheets/LM/LM336Z25.pdf
LM336 1.0% Initial Tolerance
TL431 2.0% Initial Tolerance
Atmega328 0.5% Initial Tolerance
TL431B 0.4% Initial Tolerance
When the bandgap reference is calibrated and by using gain and offset data stored in the device’s signature row Atmel guarantee accuracy better than 0.5%.
sonnyyu:
LM336 1.0% Initial Tolerance
TL431 2.0% Initial Tolerance
Atmega328 0.5% Initial Tolerance
TL431B 0.4% Initial Tolerance
Can you elaborate more? I'm lost. Thx!
Atmega328 internal AREF is better than LM336 and TL431 , close to TL431B.
Why revive a dead thread for this.
Don't confuse accuracy with stability.
Leo..
The one who confused it was sonnyyu. Nothing wrong with correcting misinformation.
Initial tolerance (accuracy) of Atmega328 internal refercence seems to be in fact 10%, not 0.5%.
So because of that - to avoid calibration - I also will be using TL431.
The only advantage of using a TL431 reference is that you don't need to calibrate.
The disadvantage of that setup is that resolution drops about 2.5 times.
Forget about a 0.1C resolution with a TL341. 0.25C steps is all you get.
The tolerance of ±10% (20%) of 1.1volt Aref is irrelevant for hobby use.
Measure once with a DMM, write it on the Arduino, and use that value in your code.
Or calibrate with melting ice.
One day you will discover the much easier to use digital DS18B20.
Leo..
Edit: If you don't want to calibrate, then it makes more sense to use an external A/D with voltage reference, like the ADS1115. Set the PGA to 2.048volt FS, and you have 15bits spread out over ~200 degrees C. Enough to get a 0.01C readout.