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Thread: Audio Shield card (Rev D)-SNAP 2

  1. #1

    Audio Shield card (Rev D)-SNAP 2

    Hello,
    After ordering the Audio shield (Rev D) and after download the circuit diagram of the board (SNAP2) I can't see the pin correspondence with the component SGTL5000. Probably the Audio Shield card (Rev D) is design for Teensy 3xx and not for Teensy 4.0. And another point is the 2 pins 'SDA' and 'SCL' are used to control 'Digital Audio Processing'
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    I wonder what is the use of using this function in the SNAP 2 ? Thank you for your answer

  2. #2
    Hi,

    Sorry now I can find the correspondence between the Audio Shield (Rev C) audio card with the Teensy 3.x of the SNAP 2 card. But I still don't understand why to use 'SDA' and 'SCL' in SNAP 2 to acquire the signal from a Hydrophone ? Probably to add an additional gain in the measurement chain ?

  3. #3
    Senior Member PaulStoffregen's Avatar
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    I'm not familiar with SNAP 2. Could you give a link to the info?

    But I can at least answer this question.

    Quote Originally Posted by DOY38 View Post
    Sorry now I can find the correspondence between the Audio Shield (Rev C) audio card with the Teensy 3.x of the SNAP 2 card. But I still don't understand why to use 'SDA' and 'SCL' in SNAP 2 to acquire the signal from a Hydrophone ?
    Briefly, the SGTL5000 chip has many configurable features. SDA & SCL are the communication port (called I2C) which is used to configure the hardware. For example, the microphone input path has 2 analog amplifiers, both with software configured analog gain. When you call the sgtl5000.micGain() function to configure how much the mic is amplified, code in the audio library uses the Wire library (which uses SDA & SCL) to communicate with the SGTL5000 chip to configure those amplifiers.

    This page on the audio design tool (right side documentation panel) shows all the functions to can call to control the SGTL5000 chip.

    https://www.pjrc.com/teensy/gui/?inf...ontrolSGTL5000

  4. #4
    Quote Originally Posted by PaulStoffregen View Post
    I'm not familiar with SNAP 2. Could you give a link to the info?
    Thank you, now I understand that it is necessary to connect the I2C bus. For the SNAP, I use this link found in this forum
    https://github.com/loggerhead-instru...ematic/LS1.PDF
    In fact, in our University (Grenoble) we have an example of this product (By Loggerhead Instruments Inc).
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    I don't know if this is the same product in this forum but one thing is sure is this card has the component 'SGTL5000' like the audio shield board you sell. According to my previous topic with the Hydrophone with -180 dB re 1V/ÁPa (http://www.hightechincusa.com/produc.../hti96min.html), I still d'ont understand with this sensibility I have 2 values which vary between 0.3ÁV and 0.1mV after Hydrophone ; and with 3.3V supply for Teensy 3.xx ; The gain is (3.3/2)/0.1mV = 16,500 -> 83dB. And the gain max with SGTL5000 is only 40dB+22.5dB = 62.5 dB.
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    So it is missing approximately 83-62.5=20.5dB thus How do they do ?
    Last edited by DOY38; 04-05-2022 at 11:26 AM.

  5. #5
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by DOY38 View Post
    So it is missing approximately 83-62.5=20.5dB thus How do they do ?
    That's really a question for the people who designed this product.

    But for blind guess, I'd imagine that blue circuit board may have a low-noise amplifier between the sensor and SGTL5000 chip, which gives the extra 20 dB gain. An amplifier might also provide a benefit of lower impedance signal into the SGTL5000, if (purely speculation) the sensor's raw output is a higher impedance than the common condenser type microphones meant for SGTL5000.

  6. #6
    Quote Originally Posted by PaulStoffregen View Post
    That's really a question for the people who designed this product.
    Yes you're right. I'm going to go back to the site to review the electronic board in blue to see if there is an additional low-noise amplifier. I'm asking this question to get an expert opinion because I think there is no need to use an additional amplifier why ?
    I think we can do : 'MIC GAIN->Analog Gain->DAP (Digital Audio Processing) Gain -> I2S Out'
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    So 40+22.5+2x6+2x12 = 98.5 dB, and that will be enough.

  7. #7
    Senior Member PaulStoffregen's Avatar
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    Looks like you're also creating multiple threads on this forum, all asking for help to essentially reverse engineer this product. Asking and guessing how things work is usually ok, as long as nobody is disclosing trade secrets obtained by inside access (especially if violating a NDA). But we take a dim view of duplicate threads on this forum.

    Please don't keep creating new threads about the same project.

    The very least you could do is give a link on each thread to the others, so when people find these conversations by searching they can see all the info, rather than only a piece.

  8. #8
    Quote Originally Posted by PaulStoffregen View Post
    Asking and guessing how things work is usually ok, as long as nobody is disclosing trade secrets obtained by inside access (especially if violating a NDA).
    I don't understand your answer, I bought a shield audio card from you and I asked how it works with my microprocessor, and we're in research (in education) and teaching and we do not sell anything and the link on SNAP that I communicated before to you is open source to my knowledge. And this topic is only about the audio shield card (SGTL5000) that I bought on this site and which has no connection with the other topics.

  9. #9
    Hello,
    About the Audio Card, do you know where I can find a mic to use the microphone input of this card ?
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    or any microphone on the market will do the trick ? I can see also this mic
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    Does it fit for Rev D Audio Card
    Thank
    Last edited by DOY38; 06-17-2022 at 09:10 AM.

  10. #10
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    yes it should fit
    Rev D Audio card has only the pins adapted to T4.x, while Rev C Audio card has pins adapted to T3.x

  11. #11
    Quote Originally Posted by WMXZ View Post
    yes it should fit
    Rev D Audio card has only the pins adapted to T4.x, while Rev C Audio card has pins adapted to T3.x
    Thank you but I don't use Teensy, I use STM32. I would like some information. With this link :
    https://www.pjrc.com/teensy/gui/index.html
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    I was able to generate the code. But on the other hand I miss '.C' and '.h' of the code, do you know how I can get it ? where can i find the component library? At the NXP provider ?

  12. #12
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by DOY38 View Post
    but I don't use Teensy, I use STM32.
    This stuff is all designed for Teensy. It doesn't work on STM32 chips.

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