Using internal AREF to create AREF/2 reference

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#1
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I have this:

    * Atmega32L
    * 3V
    * About to use internal AREF (bandgap)

I need the AREF/2 voltage in order to sample audio signal having the "zero" on between min/max values.

Can I derive this AREF/2 voltage directly from the AREF pin with resistor divider ?

How much does the AREF pin tolerate loading when using the internal reference ?

I have searched the forun and I am sure there is an answer hiding somewhere as this just MUST have been done before. Unfortunately the unclear subjects did nothing in helping to find the correct thread.

The data sheet had very little information on this subject.

Another option would be to use PWM to create the AREF/2 and stabilize it by measuring by another ADC channel.

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Page 208 of the 32(L) manual says, as in almost every other ADC-equipped AVR, that you should only connect a high-impedance voltmeter to the AREF pin, or a capacitor. So a resistor-divider is out, unless you are willing to use megohm-type values. But you could put a cmos follower with pico or nano-amp Ib characteristics there, and then divide down its output.

Roger

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Thanks !

What are my eyes made of - Wood?

Well - I really missed that one. It clearly states that the VREF just cannot be loaded at all.

I will do this using the PWM approach.

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Why give up so fast? A high-impedance-input OpAmp as a buffer should work.

Stealing Proteus doesn't make you an engineer.

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I did not "give up".

An op-amp with all surrounding components compared with one resistor and a capacitor usng the PWM approach. I like things to be as simple as possible.

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In the Ref pin only a capacitive load should connect and anyway can not be divided as it already applied to the ref pin.If you are willing to use external opamp you can use also a TL431 adjustable zener making any suitable external reference voltage.

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I do it with a divider consisting of two 470k
resistors and a buffer cap. That works very well.

The internal reference has not a high accuracy, so it
even does not matter if its changed a little bit.