Recording Audio via SAR ADC

Hardware
#1

Hi,

I was wondering, can you record audio via the SAR ADC pins.

The idea is to record audio from an analogue source such as a standard Radio via an Aux cable.

To do this one would need an ADC converter for audio and thus I would like to know if the SAR ADC would work.

I have done this on a RPI, but needed an IQaudio Codec Zero sound card using Alsa mixer and it’s Linux come line function “arecord”.

In summary I would like to know if:

  1. Is this is possible on the Le Potato without an additional Sound Card.

  2. if not would the IQaudio sound card work with this board.

  3. Are there any sound cards compatible with this board.

#2

We recommend a simple USB Microphone or USB audio input interface. They have the necessary buffering and timing to correctly record audio with proper channels and bit depth.

Using SAR ADC would require precise timing of samples which is not possible. It is rather used for other analog measurements like resistor ladder keypads and temperature probes.

You can use I2S or PCM input with Le Potato. However you need to write a device tree overlay to enable the pinmux and enable it via the libretech-wiring-tool. This requires technical knowledge.

#3

Are there any more details about the SARADC that we can use to make these kinds of decisions? I believe the only technical details available are the resolution (10 bit) and full scale voltage (1.8V).

#4

The SARADC pins are not designed to digitally sample audio as there’s no hardware for controlling timing. You should use a proper converter with buffer for audio applications. It will convert to I2S, PCM, PDM, or other formats.

#5

What about for other applications? Is any information available on noise floor, or a rough estimate of response time?

#6

You can lookup the datasheet for the SoC. It is available on Google. It is a 10 or 12 bit SAR ADC.

SAR ADC is usually used for ID or resistor ladder keypad.