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?
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.
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.
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 DesignQuestion - what is the nature of the noise:
low frequency hum or buzz, high frequency tone, wideband static, clipping or other?
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!
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.