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Thread: Codec recommendations please for standalone keyboard/sequencer

  1. #1
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    Codec recommendations please for standalone keyboard/sequencer

    Hi everyone, first post after following Paul's CS42448 build on Hackaday.io and deciding to make a keyboard-based sequencer type device for my own education in audio and to see what my children do with the result.

    I will probably get an audio shield to go with my Teensy 3.2 (which I already have) for initial playing around but I have seen elsewhere that the codec chip used in the audio shield might not be best for my eventual application (no amp? cross-talk?). Do any of you have any codec recommendations, in light of the following information:

    • I would like built in (probably mono) speaker(s) so an integrated amp is nice to have
    • I would like headphone out, preferably with sufficient insight/registers/gpio to automatically or under Teensy control switch between built in speaker(s) and headphones
    • I would like an onboard microphone, so an input for that would be good. Mic bias etc would be great.
    • Budget is up to $10 but obviously the cheaper, the more mistakes I can make!
    • I am "happy" soldering qfn 0.5mm pitch but easier to solder parts will certainly have room on the board
    • I plan to power the system from 4x AA cells although I could be dissuaded for a good reason.
    • I expect to have to put in a separate e.g. 1.8V rail.
    • Other than that, needs to work with Teensy, so I2S etc. I2C for config is fine but if it works with power-on defaults, that's great! I don't think I need any DSP etc.


    So far my search has narrowed down to the likes of the TI TLV320AIC3110.

    If you have any wisdom to offer, I'd be grateful. Thanks

  2. #2
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by smerrett79 View Post
    Hi everyone, first post after following Paul's CS42448 build on Hackaday.io and deciding to make a keyboard-based sequencer type device for my own education in audio and to see what my children do with the result.

    I will probably get an audio shield to go with my Teensy 3.2 (which I already have) for initial playing around but I have seen elsewhere that the codec chip used in the audio shield might not be best for my eventual application (no amp? cross-talk?). Do any of you have any codec recommendations, in light of the following information:

    • I would like built in (probably mono) speaker(s) so an integrated amp is nice to have
    • I would like headphone out, preferably with sufficient insight/registers/gpio to automatically or under Teensy control switch between built in speaker(s) and headphones
    • I would like an onboard microphone, so an input for that would be good. Mic bias etc would be great.
    • Budget is up to $10 but obviously the cheaper, the more mistakes I can make!
    • I am "happy" soldering qfn 0.5mm pitch but easier to solder parts will certainly have room on the board
    • I plan to power the system from 4x AA cells although I could be dissuaded for a good reason.
    • I expect to have to put in a separate e.g. 1.8V rail.
    • Other than that, needs to work with Teensy, so I2S etc. I2C for config is fine but if it works with power-on defaults, that's great! I don't think I need any DSP etc.


    So far my search has narrowed down to the likes of the TI TLV320AIC3110.

    If you have any wisdom to offer, I'd be grateful. Thanks
    That TI part you've selected looks pretty good based on what you're asking for. Personally, I'm partial to the WM8731, mainly because it's decently priced, comes in a TSSOP package (easier to solder vs QFN or BGA), includes a headphone amp, and most importantly contains a built-in digitally controlled analog preamp providing both gain and attenuation which is essential for guitar applications.

    However, in your case, it sounds like you're only interested in mic inputs, and that chip has a digitally controlled mic preamp up to 60dB (no attenuation needed if only using mic inputs and not line level or guitar inputs). It has a pretty powerful headphone amp (1.3W is pretty strong for an on chip amp) and is reasonably priced.

    Only drawback I see is the QFN, but if that's not a show stopper for you the TI looks good to me.

  3. #3
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    That's great - thank you. I appreciate you taking the time to scan over the spec and give me the benefit of your experience in this area. I hope to get a board spun up in the next month or so.

  4. #4
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    I don't know if this is something people do on here but I have drafted a schematic for a TLV320AIC3110 breakout for Teensy 3.2 (and 3.x afaik). If anyone has any feedback, please post here and I will try to improve the design before layout next week.
    Click image for larger version. 

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  5. #5
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    I forgot to add a means of connecting analogue and digital grounds. Now remedied with 4x solder jumpers which can be cut and a ferrite added to bridge them if there are issues.
    Click image for larger version. 

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    I also fell into a layout session, which is good enough to add to a run that has already gone to the fab. Should be able to test in a few weeks.
    Click image for larger version. 

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    *the uSD holder is on the back.

  6. #6
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    Are you sure you want a Teensy 3.2 as opposed to a Teensy 4? The T4 is more powerful, and it has a useful floating point unit. The audio pins are different (IE Rev D).

  7. #7
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    Thanks for pointing that out. I have a Teensy 3.2 in my parts drawer and the largest hardware uncertainty for my project is the codec/mic/speaker side at the moment. I don't think I have ever been content with a Rev 1 PCB design so I'm inclined to "get something working" and then revise the design with more long-term considerations. I will almost certainly get a Teensy 4 if I can get this working and make a version of this codec board for it. I'm sure I won't be able to reach the limits of the 3.2 in my initial testing - I know nothing about music and will consider it a triumph if I can play monotonic "happy birthday" with a square wave to begin with!

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