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Thread: Teensy 3.1 ADC LayOut

  1. #1

    Teensy 3.1: ADC PINS / 16-Bits mode

    Hi there,

    Maybe a dumb question, i've been watching this pin layout from the Teensy 3.1 (see link) http://www.pjrc.com/teensy/card5a_rev5.pdf
    In the datasheet of the processor are the pins located on pin 9 and 10 (PGA0_DM/ADC0_DM0/ADC1_DM3 (9) and PGA1_DP/ADC1_DP0/ADC0_DP3 (10)), but what are the pins on the Teensy 3.1 Board? It confuses me a little bit, haha.

    I ordered my Teensy 3.1 a few days ago. But i'm already busy with creating a custom pcb. But have no clue what the correct pins are.

    i want to convert two signals at the same time on two 16-bits channels. So, what are the two pins that i need?

    kind regards,

    Klaas
    Last edited by Chopsticks; 04-18-2014 at 01:47 PM.

  2. #2
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    See my first post at http://forum.pjrc.com/threads/25532-...for-Teensy-3-1. Especially the two pictures with the pins.
    Pins A10-A13 share different functions. You can only select one for each pin obviously.
    The library I linked to provides that function to measure two pins at the same time, but it can probably be improved if you need it.

  3. #3
    Quote Originally Posted by Pedvide View Post
    See my first post at http://forum.pjrc.com/threads/25532-...for-Teensy-3-1. Especially the two pictures with the pins.
    Pins A10-A13 share different functions. You can only select one for each pin obviously.
    The library I linked to provides that function to measure two pins at the same time, but it can probably be improved if you need it.
    I'm understanding that I can only select one function at a time, but in your post you said "Pins A2 and A3 are particulary useful for the synchronous measurement". Those pins are, as far I see 12 bits channels, what about the 16-bit channels? I thought that those two pins could used synchronous as well?

    as far i see now:
    A10 & A11 are both 16-bit ADC channels?
    both pins can either have different functions or the same function (e.g. differential or single ended)

    In Teensy 3.0 they said that due the noise the 16-bit effectively was 13 bits, is that solved in Teensy 3.1?

    Kindly regards!
    Last edited by Chopsticks; 04-18-2014 at 01:44 PM.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by Chopsticks View Post
    In Teensy 3.0 they said that due the noise the 16-bit effectively was 13 bits, is that solved in Teensy 3.1?
    No, there aren't any SAR-based ADCs with that low of a noise floor integrated on the same silicon as the digital circuitry of a 32 bit microcontroller.

    I'm reluctant to use the word "impossible" or to say this will "never" happen, because only several years ago 10 bits seemed the best achievable. But I believe it's very safe to say such a low noise floor on the same silicon as a microcontroller is well beyond today's technology.

  5. #5
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    All pins are nominally 16 bit, because they connect to the same ADC at the end (or two different ADC for a few pins in Teensy 3.1). The real resolution is worse and it will depend on many things, both hardware and software related. On the software side I can advise you to use the internal reference and maximum number of averages.

    About the synchronous thing, if you want to measure two pins at the same time you have to pick one that connects to ADC0 and other to ADC1 (A2 and A3 are the most accessible ones).

  6. #6
    Quote Originally Posted by Pedvide View Post
    All pins are nominally 16 bit, because they connect to the same ADC at the end (or two different ADC for a few pins in Teensy 3.1). The real resolution is worse and it will depend on many things, both hardware and software related. On the software side I can advise you to use the internal reference and maximum number of averages.

    About the synchronous thing, if you want to measure two pins at the same time you have to pick one that connects to ADC0 and other to ADC1 (A2 and A3 are the most accessible ones).
    ADC0_DM0(A11) and ADC0_DP0 (A10) are on the same 'ADC0' channel, So that means that they can't measure synchronous? The 12-bit ADC's A2 and A3 are also well enough. But it would be nice if it was possible to measure 2 signals synchronous with 16-bit. Maybe in the future..

    See my first post at http://forum.pjrc.com/threads/25532-...for-Teensy-3-1. Especially the two pictures with the pins.
    Is there an example in your post using the ADC's A2 and A3 (synchronous) you send me? You've send me a library with functions for ADC thought?
    Last edited by Chopsticks; 04-22-2014 at 06:37 AM.

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