does stm32h7b3i-dk Audio input support sennheiser MKE 200 microphone

[AmrithHN]

Hello,

I am trying to get a microphone (senheiser MKE 200) to work , it has TRS connector and it needs 2-10V BIAS (I think :)  )

I looked at schematics and the datasheet for the codec , MIC1 doesnt seem to have a MIC BIAS voltage support but the BSP has the below code which sets BIAS to MIC2 (which is not at all present on the board)

  /* Mic control : ADC single volume off, ADCB boost off, ADCA boost off, MicBias on AIN3B/MICIN2 pin, MicBias level 0.8xVA, MICB boost 32db, MICA boost 32dB */
  tmp = 0x03U;
  ret += cs42l51_write_reg(&pObj->Ctx, CS42L51_MIC_CTRL, &tmp, 1);

I am really confused with stm32 design, does MIC1 support BIAS ? do I need one ?

and why BIAS is applied to MIC2?

Board: stm32h7b3i-dk

Audio codec: Cs42l51

[Peter BENSCH · Accepted solution]

The  microphone MKE 200 has three connection contacts, of which only GND (large connection ring) and phantom power are used via the tip. The phantom power carries both the supply voltage (2...10V, called bias here) to which the microphone signal is superimposed.

The BSP of the discontinued codec CS42L51 itself is generic and not limited to the STM32H7B3I-DK. The codec does have the option of providing a microphone bias, but this is not so easy with the STM32H7B3I-DK because it does not provide the required hardware for this.

The codec has three stereo input channels, of which only AIN1A/AIN2A are used in the STM32H7B3I-DK. The bias voltage on AIN3B is only an alternative function of AIN3 in the CS42L51 and can of course be used for a microphone on AIN1x. You can connect the necessary phantom power resistor to BIAS/AIN3B at C75, connect it to R42/C71 or R33/C69 depending on the channel used and program the codec according to your needs.

Hope that helps?

Regards
/Peter

[AmrithHN]

Thank you @Peter BENSCH  for confirming my understanding. It will be hard to connect wires on the board , I think I will just add a pull up resistor and power it directly to the female jack on the board (much easier to solder) .

Thank you for confirming this ! have a great day!

[AmrithHN]

@Peter BENSCHI have one more question ,

Why is AIN3B/MICIn2 Bias turned on in the BSP? i found this in the repo of the same board that I use , can I turn off this Bias since I dont use MIC2 only MIC1 is wired to input ?

 /* Mic control : ADC single volume off, ADCB boost off, ADCA boost off, MicBias on AIN3B/MICIN2 pin, MicBias level 0.8xVA, MICB boost 32db, MICA boost 32dB */
  tmp = 0x03U;
  ret += cs42l51_write_reg(&pObj->Ctx, CS42L51_MIC_CTRL, &tmp, 1);

[Peter BENSCH]

tmp = 0x03U is not the address of the register, but the date that is written to the CS42L51_MIC_CTRL register (see the data sheet in my previous answer). This sets bits 0 (MCLKDIV2) and 1 (PDN_MICBIAS), which puts the microphone bias circuit into power-down status.

[AmrithHN]

Thank you Peter! I am still learning a lot now