Teensy 3.6, audio shield, Adafruit I2S microphone noise problems

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jessr95

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Hi everyone,

I'm trying to use a Teensy 3.6, the audio shield, and the Adafruit I2S microphone (https://learn.adafruit.com/adafruit-i2s-mems-microphone-breakout) to record sound to the SD card.

Here are my connections:
Microphone --> Teensy
SEL --> GND
LRCLK --> pin 23
DOUT --> Line in
BCLK --> pin 9
GND --> GND next to line in
3V --> 3V

I have adapted the recorder example to remove the play option and use of buttons as shown below.

Code: 
// Record sound as raw data to a SD card, and play it back.

#include <Bounce.h>
#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

// GUItool: begin automatically generated code
AudioInputI2S            i2s2;           //xy=105,63
AudioAnalyzePeak         peak1;          //xy=278,108
AudioRecordQueue         queue1;         //xy=281,63
AudioOutputI2S           i2s1;           //xy=470,120
AudioConnection          patchCord1(i2s2, 0, queue1, 0);
AudioConnection          patchCord2(i2s2, 0, peak1, 0);
AudioControlSGTL5000     sgtl5000_1;     //xy=265,212
// GUItool: end automatically generated code

const int myInput = AUDIO_INPUT_LINEIN;
unsigned long currentMillis;
unsigned long lastMillis;
unsigned long startMillis;
const unsigned long period = 20000;

// Use these with the Teensy 3.5 & 3.6 SD card
#define SDCARD_CS_PIN    BUILTIN_SDCARD


int mode = 0;  // 0=stopped, 1=recording, 2=playing
// The file where data is recorded
File frec;

void setup() {
  // Audio connections require memory, and the record queue
  // uses this memory to buffer incoming audio.
  AudioMemory(60);

  // Enable the audio shield, select input, and enable output
  sgtl5000_1.enable();
  sgtl5000_1.inputSelect(myInput);
  sgtl5000_1.volume(0.5);
  sgtl5000_1.lineInLevel(2, 2);

  // Initialize the SD card
  if (!(SD.begin(SDCARD_CS_PIN))) {
    // stop here if no SD card, but print a message
    while (1) {
      Serial.println("Unable to access the SD card");
      delay(500);
    }
  }
  startMillis = millis();
}


void loop() {
  currentMillis = millis();
  startRecording();
  Serial.println("Recording..");
  while ((currentMillis - startMillis) <= period) {
    continueRecording();
    currentMillis = millis();
  }
  if (currentMillis - startMillis > period)
  {
    stopRecording();
    Serial.println("Stopped recording.");
    while (1);
  }
}


void startRecording() {
  Serial.println("startRecording");
  if (SD.exists("RECORD.RAW")) {
    // The SD library writes new data to the end of the
    // file, so to start a new recording, the old file
    // must be deleted before new data is written.
    SD.remove("RECORD.RAW");
  }
  frec = SD.open("RECORD.RAW", FILE_WRITE);
  if (frec) {
    queue1.begin();
    mode = 1;
  }
}

void continueRecording() {
  if (queue1.available() >= 2) {
    byte buffer[512];
    // Fetch 2 blocks from the audio library and copy
    // into a 512 byte buffer.  The Arduino SD library
    // is most efficient when full 512 byte sector size
    // writes are used.
    memcpy(buffer, queue1.readBuffer(), 256);
    queue1.freeBuffer();
    memcpy(buffer + 256, queue1.readBuffer(), 256);
    queue1.freeBuffer();
    // write all 512 bytes to the SD card
    //elapsedMicros usec = 0;
    frec.write(buffer, 512);
    // Uncomment these lines to see how long SD writes
    // are taking.  A pair of audio blocks arrives every
    // 5802 microseconds, so hopefully most of the writes
    // take well under 5802 us.  Some will take more, as
    // the SD library also must write to the FAT tables
    // and the SD card controller manages media erase and
    // wear leveling.  The queue1 object can buffer
    // approximately 301700 us of audio, to allow time
    // for occasional high SD card latency, as long as
    // the average write time is under 5802 us.
    //Serial.print("SD write, us=");
    //Serial.println(usec);
  }
}

void stopRecording() {
  Serial.println("stopRecording");
  queue1.end();
  if (mode == 1) {
    while (queue1.available() > 0) {
      frec.write((byte*)queue1.readBuffer(), 256);
      queue1.freeBuffer();
    }
    frec.close();
  }
  mode = 0;
}


I'm able to record to the SD card successfully, when I import the file into Audacity you can hear music playing in the background but there is so much noise in the recording too.
I know the audio library is set up for 16-bit data and the microphone outputs 24-bit so I don't know if that's the problem, however, I have seen in others have managed to get this microphone working.

Does anyone have any ideas how to fix this please? The recording and wiring photos can be found here: https://drive.google.com/drive/folders/1hZaF_oPHFYxPeRJft5oK1y-HC7paSW5i?usp=sharing

Thanks in advance!
 
Okay, thanks, so if I connect DOUT to mic instead and keep the other connections the same should that work?
 
jessr95 said:
Okay, thanks, so if I connect DOUT to mic instead and keep the other connections the same should that work?
Click to expand...

No.
mic is for analog microphones, not i2s microphones.

You can't connect it to the audio shield.

BUT:
The shield outputs a I2S signal, too. You could perhaps disconnect that pin and connect DOUT to the teensy, instead.
But I really don't know if that works.

Ways easier and without hassle would be to just use a analog mic.
 
So just to confirm, I can't use this microphone with the audio shield at all? Can I use it with just the Teensy?
 
Yes, if you don't use the audioshield. Or, as said above, you can try to just disconnect the pin and connect the mic there, instead.

But, really, I don't know if that works. Maybe yes.

I2S = Digital Audio


Edit: Using a cheap analog mic would be so much easier... you can get them for a few cents.
 
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