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Thread: Voltage reference for Teensy 3.2

  1. #1
    Junior Member
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    Jan 2018
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    Voltage reference for Teensy 3.2

    Hi all

    I'm working on a proyect involving readings from several potentiometers with Teensy 3.2. Everything works fine, but now I'd like to improve precission. As far as I know the Teensy 3.2 ADC is default set to 10 bit, but I'd like to use 12 or even 13 bits.
    In order to do that I'm thinking about:
    - A more stable voltage reference attached to AREF pin than the internal reference.
    - A stable Vcc applied to the potentiometers.

    I'be never worked with this kind of IC's. Is any voltage reference IC recommended for this? Also, would it be a good idea to use the same voltage reference output to feed all the potentiometers, or is better to use the 3.3v regulator inside the Teensy for the potentiometer rail?

    Thank you!

  2. #2
    Senior Member+ Theremingenieur's Avatar
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    To make it simple, I'd use the 3.3V as ADC reference and as supply for the potentiometers. These 3.3V might be unstable and dirty, but since the Vref and the potentiometer supply would vary together, errors would compensate. You might thus read potentiometers with 12bit resolution by respecting some technical details: NXP recommends to keep the source impedance low in order to get good precision with these delta-sigma converters (using potentiometers <= 10kOhm) and to add a 10nF capacitor from the wiper to GND.

    Afterwards, when it comes to manually actioning potentiometers, 12bit resolution might be an overkill. 270 rotation angle (for a standard pot) divided by 4096 steps is ways beyond manual precision. So, you might consider using rotary encoders instead.

  3. #3
    Junior Member
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    Thank you for your answer Theremingenieur.

    NXP recommends to keep the source impedance low in order to get good precision with these delta-sigma converters (using potentiometers <= 10kOhm) and to add a 10nF capacitor from the wiper to GND.
    Yes, all my potentiometers are 10K, and have a 10 nF cap in the wiper. Unfortunatelly I've tried to use the 3.3v internal reference for AREF pin and also for the potentiometers supply before, but I couldn't use more than 10 bits dure to the noise. That's why I'd like to improve the whole thing with an external voltage reference chip.
    Regarding the precission, eventually this proyect will become an OSC controller (like MIDI, but with a lot more usable bits). So using 12 or even 13 bits makes sense to me. I guess encoders would sort out this noise issue, but I prefer the analog feel of the potentiometes ^^U

    Thank you again!

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