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Connecting AVCC and AREF on ATmega with Internal 2.56V ADC Reference

schabik89 15248 8
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  • #1 9187722
    schabik89
    Level 10  
    Posts: 31
    Listen, I have a problem, I`ve been looking for some time and I can`t find a clear answer - namely:
    I want to know exactly what I should pull up the AREF and AVCC pins to, through what and to what value since I have set the ADC reference in the Bascom as internal 2.56[V].
    From what I have established so far, I conclude that AVCC is a 10uH choke for the power supply and AREF is probably a capacitor for ground.
    Please help
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  • #2 9187970
    tmf
    VIP Meritorious for electroda.pl  
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    You concluded correctly. Details are in the processor catalog notes.
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  • #3 9187973
    MirekCz
    Level 35  
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    Yes, a 100nF capacitor between AREF and GND.
    AVCC by 10uH to VCC.

    This is a simple and effective way of filtering voltages, which improves the accuracy of measurements. Although in the case of ATMEGA CPUs they are never overwhelming ;-)
  • #4 9384466
    schabik89
    Level 10  
    Posts: 31
    Listen, after connecting the system, can I use a meter to measure how much my supposed internal 2.56 AREF actually has?
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  • #5 9384498
    dondu
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    Judging by this diagram, it is on the AREF pin:

    Connecting AVCC and AREF on ATmega with Internal 2.56V ADC Reference
  • #6 9384668
    _Robak_
    Level 33  
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    Yes, that is why when turning on the internal 2.56V source, you must not connect anything to Aref because there is a short circuit.
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  • #7 9384998
    drzasiek
    CNC specialists  
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    But if you use a stabilizer, it is better to connect AREF to the uC power supply and set it to external. The internal voltage likes to oscillate more than after the worst stabilizer.
  • #8 9385036
    dondu
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    Part of the cure for this is sleep mode ADC noise reduction .
  • #9 9385752
    mirekk36
    Level 42  
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    drzasiek wrote:
    But if you use a stabilizer, it is better to connect AREF to the uC power supply and set it to external. The internal voltage likes to oscillate more than after the worst stabilizer.


    Why, my friend ;) .... setting the reference voltage to extrenal is done without the need to connect it to AREF if it is to be VCC. This is definitely safer - especially if you accidentally switch to 2.56 internal. So AREF should still be connected via 100nF to GND.

    Once in place, an external, specialized reference source with values other than internal or VCC is connected to AREF.
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Topic summary

✨ The discussion revolves around connecting the AREF and AVCC pins on the ATmega microcontroller while using the internal 2.56V ADC reference. Users confirm that a 100nF capacitor should be placed between AREF and GND, and AVCC should be connected through a 10uH choke to VCC for effective voltage filtering. Caution is advised against connecting anything to AREF when the internal reference is enabled to avoid short circuits. It is suggested that for improved stability, AREF can be connected to the microcontroller's power supply when using an external reference. Additionally, using sleep mode can help reduce ADC noise.
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