Recording audio?

OpenMV Products
1

We want to record images of animals in a nature conservation project, and also birdsong: initially as audio clips on the SD card but later perhaps for processing onboard - see here, for instance: Birdsong analysis and visualisation | The Cacophony Project

In our case audio and video processing do not have to be simultaneous.

Cheap digital microphones are available, with the I2S interface.

Q1 - has anyone attempted to record sound on the OpenMV?
Q2 - are I2C pins available on the OpenMV?

Thx - Charles

2

Hi, I’ve seen a few attempts on the forums to play WAV files, but no recording, and yes we have two I2C interfaces on the pin header.

3

The ADC pin can record audio. However, there’s no driver software to make a WAV file for this.

4

Hmmm - I have found some background that might be of value if anyone wants this feature…

I have never interfaced to digital audio products. I had heard of I2S (which is different from I2C) as an audio interface.
And the ST processor supports this interface. It seems it needs three pins: in effect clock, data and sync (called WS).
When WS is low the left data is clocked out and when WS is high the right data. Microphone chips have a left/right select pin,
so if you want stereo you can connect two chips in parallel with their selects wired differently.

From what I can see, The OpenMV camera can support I2S on the pins provided for SPI interface (possibly - is this right?):
PB12 = SPI2_NSS on JP1 pin 7 = I2S2_WS
PB13 = SPI2_SCLK on JP1 pin 3 = I2S2_CK
PB14 = SPI2_MISO on JP1 pin 2 = I2S2_SDI (audio in?)
PB15 = SPI2_MOSI on JP1 pin 1 = I2S2_SDO (audio out?)

An example of a digital microphone with an I2S interface is the Ivensense ICS-43434: https://invensense.tdk.com/wp-content/uploads/2016/02/DS-000069-ICS-43434-v1.2.pdf Modules with these may be available, for instance here: ICS-43434 I2S Digital Microphone Breakout Board - SensorMaestros
Other I2S digital microphone modules seem to be available.

As for the software - I don’t know. Someone has got this working on an STM32 chip:

This person has done it in Python for the ESP32: I2S Microphone | Details | Hackaday.io

This this seems to describe a MicroPython I2S library (but is it only for ESP32?): GitHub - miketeachman/micropython-esp32-i2s-examples: Usage and examples for I2S support on the ESP32 microcontroller

5

If there’s an I2S interface on SPI2 then you just need to write a C driver and then you can support a Microphone. The STM32 hardware will take care of audio data reception.

6

Yes, I also want this feature. So it there any plan to integrate the I2S interface into openmv? :grinning:

7

It’s too much to add to the plate right now.