Precision Voltage Reference - Arduino ADC External Aref Input

[@GnuReligion]

Now I have to check out those LM4041 shunt regulators. My LM431's need a LOT more current to regulate. Usually use 8mA or more.

[@GadgetReboot]

Yeah that sounds like a lot, like using a Zener. I never thought to try measuring the actual current it used but the pcb sockets make it easy to hook up (finding the time is the real issue). I wish I had a good auto-ranging current measuring thing on hand so I could scope stuff like that. Maybe I should try to implement the uCurrent Gold, I think someone made an auto-ranging version of that.

[@p_mouse8676]

That really depends on the type of "431" you're choosing. The TL431 is basically stable from say 100uA and up I personally like to go for the TLV431B version (0.5%), which has a 1,2V reference (there are other ones available) Just check the datasheet for reference.

[@KirstyTube]

I really wish the built in Nano 5v ref was more accurate. Supplying it with regulated 5v on the VIN pin and the ref is showing 4.6v meh. I'm not comfortable connecting this supply to the AREF pin or will it be fine ?I know the nano has a built in 32k resistor on the AREF input but I really don't like letting the magic smoke out lol. I have ordered some TI LM4040 5v references to try them out (the data sheet from RS components is awesome / example diagrams :).

[@GadgetReboot]

Looking on page 319 in this bigger version of the ATmega data sheet www.mouser.ca/datasheet/2/268/ATmega48A_PA_88A_PA_168A_PA_328_P_DS_DS40002061B-1900559.pdf It looks like Aref max would be VCC + 0.3v worst case. I didn't look into the actual structure of how Aref and Vref are connected internally, but if the pin is unconnected, and is enabled in a sketch rather than any other internal reference, maybe it measures an idle voltage as a result of other things in there but applying 5V would be ok as long as the VCC of the chip is getting 5V and it's not exceeded........ So if you measure 4.6v on Aref, is that with a sketch running that is set for using VCC as the analog ref? Once you set it to use the external Aref pin, I'd say it should be safe to apply up to the actual VCC pin's voltage.

[@electronic7979]

Helpful video 👍

[@taranagnew436]

What use cases does the aref have?

[@7alfatech860]

Couple of possibilities: Increase the dynamic range of the ADC, as he mentioned. By using an Aref closer to the expected max measured voltage, one gets better resolution. Another possibility is to increase the accuracy of the conversion: using Vin as the reference voltage is only as accurate as the output of the power supply, and may vary with varying demands.

[@orhanyor]

Might be a noobie question but can you please tell me, will I be able to use the full range of the potentiometer if its supplied with 5V to a 5V arduino while it uses 2.5V as an ADC reference, or it will be limited to the half of the range. Like for example if the pot has 180 degrees of wiper range, will it just stop at 90 degrees because it will provide 2.5V at that point to the analog input of the arduino?

[@GadgetReboot]

The analog input voltage is limited by the ADC reference voltage so if it is a 2.5 V reference then the reading will just max out at 2.5 V and if there’s any higher voltage you will just read the maximum still of 2.5. The only thing to consider is depending on the chip, it might not tolerate input voltages higher than whatever the ADC reference is or maybe it can still tolerate 5 V, I forget what Arduino is capable of so the specific chip datasheet would have to be looked at to be sure.

[@cyklop1977]

Ok