OVMS3-idf/examples/peripherals/i2s_adc_dac/README.md

I2S built-in ADC/DAC Example

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• This is an example of:
  • Recording sound from ADC
  • Replay the recorded sound via DAC
  • Play an audio file in flash

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• Run this example
  • Set partition table to "partitions_adc_dac_example.csv" in menuconfig, or rename sdkconfig.default to sdkconfig directly.
  • Set IDF_PATH and run "make flash"

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• This example will execute the following steps:
  1. Erase flash
  2. Record audio from ADC and save in flash
  3. Read flash and replay the sound via DAC
  4. Play an example audio file(file format: 8bit/8khz/single channel)
  5. Loop back to step 3

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• Hardware connection:

  ESP32	Microphone + amplifier	amplifier + speaker
  GPIO36(ADC1CH0 input)	data output pin
  GPIO25(DAC1 output)		right channel speaker input
  GPIO26(DAC2 output)		left channel speaker input

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• How to generate audio files:

  • tools/generate_audio_file.py is an example of generate audio table from .wav files.
  • In this example, the wav file must be in 16k/16bit mono format.
  • generate_audio_file.py will bundle the wav files into a single table named audio_example_file.h
  • Since the ADC can only play 8-bit data, the script will scale each 16-bit value to a 8-bit value.
  • Since the ADC can only output positive value, the script will turn a signed value into an unsigned value.

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• Note:
  • DAC can only play 8-bit data, so the wav file data are scaled to 8-bit data.
  • I2S DMA can only output 16-bit/32-bit data to DAC, DAC will only take the highest 8-bit data and output accordingly.
  • Before I2S DMA can output data stream to DAC, the data format should be converted to 16-bit or 32-bit by padding zeros.