I need to record audio with STM32. I've got electret microphone and pre-amp based on MAX9812.

This is a schematic from datasheet:

How I can connect this pre-amp to the ADC? If I just connect it as-is I will get only positive half of wave, so I need some shift +Vcc/2. How can I do this? Maybe I can just remove output capacicator? Also, STM32 has differential ADC. Maybe I can use it here?

  • \$\begingroup\$ What does the ADC data sheet recommend? Have you read it yet? \$\endgroup\$
    – Andy aka
    Mar 4, 2018 at 10:59
  • 2
    \$\begingroup\$ Errrm. That chip has only a single rail. Its output would just about have to be at Vcc/2 already. If you check at pin 3, you can see if it has a DC offset. \$\endgroup\$
    – JRE
    Mar 4, 2018 at 11:12

1 Answer 1


MAX9812 has a DC offset of VCC/2 on pin 3 already. So yes, you can drop the capacitor and connect directly.

If this was not the case, you would keep the bypass/FC-blocking capacitor and use a resistor to add the DC component. For example a 100k ohm resistor connected to VCC/2. VCC/2 can be made with a voltage divider of say 1k ohm resistors.


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