Forum Rule: Always post complete source code & details to reproduce any issue!
Page 2 of 2 FirstFirst 1 2
Results 26 to 32 of 32

Thread: Teensy 3.2 DAC -> full AC signal generator / LFO for audio

  1. #26
    Junior Member
    Join Date
    Dec 2012
    Posts
    18
    One thing that would simplify having more than one setup at a time (I didn't go nuts buying $8 dac chips that I need to reflow) would be using the built in 12bit DAC in the Teensy 3.2. Can anyone see an issue with using the Teensy's DAC assuming I use my 2.5 voltage reference into AREF on the 3.2? At this stage, I know I can get the quality I need when I use my external DAC, but at this point, I'm working on interface, and it's helpful to have a more portable (less encumbered by a tssop breakout board) option with just my Teensy, screen and pocket scope. I've essentially copied the output circuit from Peaks, and it works like a charm - can't really think of a reason it wouldn't work if I fed it the correct vref, but it seems that every time I think I've got a handle on how everything works, I'm missing something vital :P

    Thanks!

  2. #27
    Senior Member
    Join Date
    Feb 2013
    Posts
    563
    Quote Originally Posted by brucethehoon View Post
    One thing that would simplify having more than one setup at a time (I didn't go nuts buying $8 dac chips that I need to reflow) would be using the built in 12bit DAC in the Teensy 3.2. Can anyone see an issue with using the Teensy's DAC assuming I use my 2.5 voltage reference into AREF on the 3.2?
    the DAC won't track AREF, only the ADC does. so you'll end up with either 3v3 (= VDDA) or the internal reference, which is 1v2, IIRC.

    other than that, it shouldn't make much of a difference, ie for working on the interface. to some extent of course that will depend on what else is going on; e.g. will there be any other SPI devices involved etc.

  3. #28
    Junior Member
    Join Date
    Dec 2012
    Posts
    18
    Whoopsie! And that's why I asked. Thanks so much for helping me avoid that mistake!

  4. #29
    Junior Member
    Join Date
    Jun 2014
    Location
    Helsinki
    Posts
    2
    Resurrecting this thread just to say that a eurorack/teensy platform will be great and hopefully, will happen one day! Max (Mxxx) work have shown how much can be accomplished integrating the teensy and a modular.

  5. #30
    Junior Member
    Join Date
    Mar 2015
    Posts
    19
    Quote Originally Posted by PaulStoffregen View Post
    An idea I've toyed with involves making another audio adaptor board, specifically for people building Eurorack modules. If this ever happens, which is a pretty big "if", a realistic time frame would likely be early 2017. After the 180 MHz Teensy is released, and after the audio lib gets a granular synthesis engine and wavetables and more effects and more signal-modulated features, this sort of thing might make more sense (where "sense" means maybe enough of market... maybe?)

    Such a module would have two SGTL5000 chips, with 4 DC coupled inputs and 4 DC coupled outputs. All 8 would be capable of +/- 10V signal range, or 8V or 5V, software configurable using the adjustable line-level in/out of the SGTL5000. Lower ranges like +/- 2.5V would need to be done in software, using only a portion of the hardware's analog range. Unipolar CV would just use the positive half. Of course, all 8 signals would have the full 16 bit, 44.1 kHz audio sampling and integrate with the audio library data flows.

    I'd probably put a tiny EEPROM chip on the board. During testing here at PJRC, we'd do a room temperature characterization of the DC offsets and maybe also the exact signal gain. These would take into account both SGTL5000 level and resistors & offset voltages/currents in the opamp circuits. For applications that need to get very low DC offset voltage and precise signal levels, that info could be read and used for software-based correction.

    It would probably also have a place to solder a 10 pin Eurorack power header, and it'd have a 12V to 3.3V step-down power supply to power the Teensy and codec chips. Filtered, reverse polarity protected +/- 12V would be passed through the pins to allow the rest of the module to get its power.

    This wouldn't be a complete Eurorack module board. The idea is it's be a component used in one. It'd be the same 0.7 inch wide as Teensy, and probably 1.2 to 1.5 inches long. It and a Teensy would fit onto the back side of another board or stack of boards that provide the user interface, plus any other signal inputs or outputs.

    Realistically, such an audio board would retail around $20 to $25. Together with a Teensy, that's about $40 to $50 for the DSP analog I/O infrastructure on the back layer of a module. By the time another board, pots, buttons, front panel and other stuff are added, it's not such a cheap way to make a Eurorack module. But maybe it'd be worthwhile, for the many DIY possibilities it might open up?

    I know several Eurorack module builders are here, and please feel free to link to this thread from forums like MuffWiggler. I'm curious to hear any feedback. But please remember, this is only hypothetical so far, and if it does ever happen, the earliest likely timeframe would be in 2017.
    is this still under consideration?

    I think (especially with teensy 4.0) there is a lot of potential in building eurorack modules from teensies, as long as the audio/CV in/out is available as a shield such that one does not have to reinvent the wheel all the time.

  6. #31
    Member
    Join Date
    Nov 2012
    Location
    Olympia, WA
    Posts
    54
    Well, there is this from 1010 music: https://1010music.com/product/euroshield1

    Also the Ornament and Crime Module is crazy popular, among other Teensy based modules. Things have progressed since 2016. Nothing Teensy 4.0 that I know of, yet.

  7. #32
    Junior Member
    Join Date
    Mar 2015
    Posts
    19
    Quote Originally Posted by drjohn View Post
    Well, there is this from 1010 music: https://1010music.com/product/euroshield1

    Also the Ornament and Crime Module is crazy popular, among other Teensy based modules. Things have progressed since 2016. Nothing Teensy 4.0 that I know of, yet.
    thank you for your answer.
    I think the euroshield is somehow a too limiting approach, since the number of outputs/inputs as well as the module layout, i.e. the knobs etc. is predefined.
    A general shield which just provides audio/CV inputs/outputs (maybe with OP amps integrated for input and output, although this is debatable) and passes through all the other teensy pins would be more versatile

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •