I am writing a program to continuously save 12-bit acoustic recordings from a [microphone using the the RP2040’s in built ADC. The ADC works just fine, however, I have to write buffered acoustic data multiple times per second to the SD card. When the SD card is writing, it creates low level broadband noise on the ADC (see spectrogram image below - the SD card noise are the faint vertical lines).
A few observations.
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The noise is present when the microphone is replaced by a resistor. It is also present using different types of microphone.
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Connecting the microphone to an external battery (grounds connected) helps but does not get rid of it entirely.
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When the board is connected via USB power, then the overall noise in the recordings is greater but the SD card noise is no longer present (or perhaps drowned out by the increase in noise)
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The noise only occurs when the SD card is writing.
Has anyone else come across this issue/have any suggestions on how it might be solved. Any help much appreciated.
A spectrogram of the noise on the acoustic recordings. ](https://www.digikey.co.uk/en/products/detail/adafruit-industries-llc/1063/4990762?utm_adgroup=Evaluation%20and%20Demonstration%20Boards%20and%20Kits&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Development%20Boards,%20Kits,%20Programmers&utm_term=&productid=4990762)