This is further extension of my last work of ESP-32 with PCM5122 DAC sound card. In this we have interfaced an I2S MEMS MIC INMP441 from TDK INVENSENSE with ESP-32 along with DAC PCM5122 to implement a Record capture Loopback Playback in our ESP-32 EspressIF C/C++ Application. The INMP441 is Omnidirectional MEMS MIC with good Sensitivity of -26 dBFS, 61dBA SNR with maximum Acoustic Overload Point of 120 dB SPL.

Now some Pros of using I2S MEMS MIC are:
1. Eliminates the need for adding Audio Codec or Audio DSP processor to do the ADC conversion and Decimation & Filtering associated with PDM to PCM conversion.
Due to this we can directly interface with I2S master as Micro-Controller or SOC as we have done in this demonstration too, of interfacing it directly with ESP-32 on I2S.
2. Small compact size in the form of SMT package. Low current consumption of ~1.5 mA.

The CONs of using I2S MEMS MIC are:
1. Only 24-bit PCM, Philips I2S format is supported. There is just no way any other format can be supported. No configuration registers to program or Pins to set for that matter. Another I2S MEMS Mic #Knowles SPH0645LM4HB is not conformant to I2S format due to Timing issues and so can't be used to READ I2S data. So, only 32/24-bit PCM, I2S format is supported.
So, please check if your I2S Master MCU or SOC supports 32-bit PCM, I2S format before using this MEMS MIC in your project.
2. The GAIN of these MICs are also not configurable & there is just no way GAIN of these I2S MEMS MIC can be configured by programming or by setting pins.
3. More Pins are required to Interface as against PDM based Digital MEMS MICs or Analog MEMS Microphones.

So, in short these I2S MEMS MICs save you the overhead of PDM PCM conversion & Decimation but Decimation factor is fixed to 64 only in these I2S MEMS MICs due to which only 32-bit PCM is supported. Never think of trying with 16-bit PCM as you will never be able to sync the frames correctly in I2S channels.

Luckily ESP-32 supports 32-bit PCM due to which I was able to share LRCK& BCLK lines of DAC PCM5122 which is also programmed to support 32-bit PCM Playback, 48kHz using our ESP-32 Driver which I wrote previously. Now the Word Select(WS) signal of INMP441 MIC is tied to LRCK signal, which ensures Stereo Capture of both Left & Right channel as LRCK varies between HIGH & LOW of 48kHz clock. In this Application we are doing I2S READ using DMA of Capture/RECORD samples of INMP441 MIC and these READ samples, we do I2S WRITE using DMA to write to PCM5122 for Audio Playback. Thus a Loopback of I2S READ to I2S WRITE is done here via our ESP-32 Application to provide a RECORD PLAYBACK loopback instantaneously like a Live MIC session.
The Volume that we are increasing/decreasing is that of Playback section, the AMP section or DAC section & not Record section.

свернуть