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Thread: teensy 3.6 and pin A11 A10 AREF

  1. #1

    teensy 3.6 and pin A11 A10 AREF

    hi,

    What is this pin ?

    What's its use pin AREF ?

    Thanks

  2. #2
    Senior Member+ KurtE's Avatar
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    First with A10, A11 and likewise A25 and A26 - There are analog only pins. That is you can only use these pins to do things like analogRead.

    AREF - analog reference pin - I have not used it myself, but it allows you to set an external reference voltage to be used by the analog to digital conversion.
    This voltage I believe must be <= 3.3v.

    I know with the ADC library you can then choose to use this as your reference voltage by the setReference call that allows you to choose, to use this or not

  3. #3
    thank you.

  4. #4
    AREF in teensy 3.6. Hi ive been looking at the documentation. But where is the AREF pin of the teensy 3.6?

  5. #5
    Senior Member+ Theremingenieur's Avatar
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    Besides A10 and A11 in an inner pin row besides outer pin 23.

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    Hi,i want to use the aref pin in the teensy 3.6.This pin will connect with the output of a ldo voltage regulator ~3.3v and i want to ask some things.

    1)We connect the output voltage ~3.3v directly to the pin AREF??You will need to connect extra capacitors, some resistance or ferrite in series to this pin??

    2)The AREF pin is related to analog pins A10 and A11??So when using external reference voltage we should use the analog pins A10 - A11 or any analog pin??

  7. #7
    Senior Member+ Theremingenieur's Avatar
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    The Teensy has two internal ADCs. All analog capable pins can be switched to one of the two ADCs by an internal multiplexer when a command like analogRead is invoked. The Teensyduino core (or, for extended functionality, the ADC library) takes care of that. The hardware allows to either use an internal bandage reference, Vdd, or the AREF input voltage for each of both ADCs independently.
    Pins A10 and A11 are somewhat special, since these are “analog only” which means that they can not be used alternatively as digital GPIO pins like A0-A9. And they give the option to be used as either independent analog inputs, or to be “coupled” for differential measurements. But to explore these options, you need the ADC library, the standard functions do not support such special modes.

  8. #8
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    Ok, thanks for the analytical explanation.

    Quote Originally Posted by thanos View Post
    1)We connect the output voltage ~3.3v directly to the pin AREF??You will need to connect extra capacitors, some resistance or ferrite in series to this pin??
    Can you suggest me something?

  9. #9
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    concerning external VREF
    if you look into schematic https://www.pjrc.com/teensy/schematic.html you will see that VREF is already connected to 3.3V. So, by program VREF to use 'external' puts it to 3.3V. IMO, if you put lower reference voltage that must be designed properly to not to short VREF.

  10. #10
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    Quote Originally Posted by WMXZ View Post
    concerning external VREF
    if you look into schematic https://www.pjrc.com/teensy/schematic.html you will see that VREF is already connected to 3.3V. So, by program VREF to use 'external' puts it to 3.3V. IMO, if you put lower reference voltage that must be designed properly to not to short VREF.
    You are right.....if i want to use external reference i have to remove the 470Ω resistor?

  11. #11
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    Quote Originally Posted by thanos View Post
    You are right.....if i want to use external reference i have to remove the 470Ω resistor?
    NO, the teensy are made such that all foreseen functionality is available without HW mods.
    what I mean is that your VREF generation must tace of the existing connection to VDD. Not really sure, if connecting VREF to ground would stop Teensy, but I'm NOT eager to try it.

  12. #12
    Senior Member+ Theremingenieur's Avatar
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    Read the data sheet. VREF May not go below 1.1V! When providing an external VREF, the 470R can remain in place. Some external references do need a bias resistor and there, you have already one.

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