EEVblog® Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: EdenPal on September 29, 2026, 12:47:27 pm
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Hi All,
I'm new here.
I designed a PCB with ESP32 (standalone chip) and I connect microphone to the ADC pin of the ESP.
Claude wrote code for this design that the ESP32 will stream the sound to my phone by the WiFi channel.
I hear the sound but it is very noisy. I tired to add a software LP filter but it is still very noisy.
In addition, I added a hardware LP filter (RC filter after the opamp) and it still noisy.
I added the project file (EasyEDA) to this message.
Anyone can help me to understand what no good with my design?
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Desolder L5 and connect an independent battery to C63; this way we will find out if the noise is transmitted through the power supply.
LMV321 has high noise, but I don't think it is the main cause.
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A low signal amplitude into the ADC can be the cause.
In addition to the previous suggestion, can you check for us the DC voltages, referenced to GND, on:
1) pin 1 of the microphone (must be >1.8V)
2) MIC_out (must be 1.65V)
3) Node "1.65Vref" (must be 1.65V)
4) Pin 3 of U12 (must also be 1.65V)
That way we could check if the mic + preamp biasing and supply levels are OK.
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Your post got me curious about how the mic and preamp works.
Found an excellent detailed reference design by TI of your topology (see attached file.)
Single-Supply, Electret Microphone Pre-Amplifier - TI Reference Design
Question - what is the nature of the noise:
low frequency hum or buzz, high frequency tone, wideband static, clipping or other?
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Thank you very much for your answers.
marco.van.steen, about your answer, I checked all the voltage nets before I continued to the code.
MariuszD, thank you for the idea. I supply the microphone circuit with battery, like you said and the noises disappear.
Do you think that if I will add capacitance to the buck converter it will help?
I try to think what to do for the next project with sensetive analog design with DC-DC cirucit that supply it (not LDO).
Thank you very much!
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Try to make a better filter, use a large inductance for L5 and a higher capacitance in parallel with C57.
If you have an oscilloscope, check the ripple on the 3V3 and 3V3_f rails.
L5 can also be replaced or connected in series with a resistor of a few hundred ohms.