Auto Analog Audio & NRF52840: Now working on non-Mbed cores

 Auto Analog Audio & NRF52840: Now working on non-Mbed cores

Playing around with the AAAudio library

So I finally decided to make the necessary purchase and get myself a relatively cheap oscilloscope, and with that play around more with the AAAudio library. Even with the added view into the output signal and what is going on using the scope, I still haven't been able to figure out what I'm doing wrong with the I2S interface, so for now the audio is not of the highest quality, which is relatively good for voice, but not so good for higher frequency audio signals.

I have, however, made progress on using the non-MBED core for both input and output of audio using the PDM (microphone) and PWM (amp/speaker) interfaces, which opens up more of the capabilities of this device! In the end, once I actually quit working with the I2S interface, it wasn't that difficult getting the non-MBED core to work. This means that AAAudio should work on other devices like the Feather 52840 Express etc, but it hasn't been fully tested yet. The PWM interface can handle ~10-bit audio at 16Khz, and lower at higher sample rates.

It also allows users to adjust between 20khz and 16khz PDM samples now as well!

Users can specify which pins to use for PWM by editing the library src/NRF52840/AutoAnalogAudio.cpp file and specifying the GPIO pin and port numbers, else it defaults to GPIO #5, port 0 for output.

As of this writing, users would need to download and install the library from ZIP directly from here because I will not do a new release for a while. (Still testing and potentially updating the new capabilities)

AutoAnalogAudio Arduino library updated with ESP32 Support

 AutoAnalogAudio Arduino library updated with ESP32 Support

ESP32 DAC/ADC Output/Input via the I2S peripheral

Previously this year, I received some ESP32 based MCUs with OLED displays from DigitSpace, and used these devices to add ESP32 support to the AutoAnalogAudio library. It is a bit different from previous iterations, since instead of AVR interrupts and PWM, the ESP32 uses much more advanced peripherals. The I2S capabilities of the ESP32 provide a fairly seamless interaction when in/outputting audio signals, since it is just a matter of configuring the I2S, DAC and/or ADC and feeding and/or drawing data from the device. The main challenge in this case was combining the I2S functionality with RTOS tasks to provide a simple, asynchronous audio interface as is the case with the AutoAnalogAudio library.

The capabilities are much the same, but the ESP32 portion is still a bit in development, although working nicely at this point. The ESP32 example is specifically for the ESP32 device, since some minor API changes were required to manage RTOS tasks in combination with the I2S peripheral. This allows asynchronous handling of audio, so users can start playback and manage other tasks however desired while audio playback occurs.

Hardware:

1 x ESP32 OLED Wifi Kit
1 x MAX9815 Microphone Preamp
1 x TDA7297 PA Module

The MAX9815 will provide some audio to sample, and the TDA7297 was used to amplify the output of the onboard DAC. The above hardware as mentioned is provided by DigitSpace.

Connecting the Hardware:

With the ESP32, the AAAudio library samples the ADC on analog channel 4 by default, and sound output is on DAC1 and/or DAC2 (See previous post for pinout) The ADC channel cannot currently be changed, but that is on the to-do list.

Limitations:

The ESP32 onboard ADC will provide relatively good quality audio sampling, at 12-bits. The onboard DAC however, is only 8-bits, so the output will not be quite as high quality as with the Arduino Due. Using a higher sample rate can make up a for the low bit-rate of the DAC, as higher sample-rate * bit-rate = quality.

Overview:

Updating the library for ESP32 support has been fairly interesting, as it required a fair bit of learning and development time to understand I2S and how to control the related peripherals, while providing the same or similar behavior as with currently supported devices like the Due or Uno.

All in all it seems to perform pretty well. Audio input or output from virtually any source can be managed via the AAAudio library.

The updated library has been released and should be available via the Arduino Library Manager.

Source Code: https://github.com/TMRh20/AutoAnalogAudio
Documentation: http://tmrh20.github.io/AutoAnalogAudio

Testing New RF24 Arduino Library Fork for NRF24L01 Radio Modules: Comparative Testing - Transfer Rates

Overview:

Per my previous blog posts, I have been working on some improvements to the RF24 radio library, and the main benefits of the changes have been realized. The following video compares the difference against the fork found at https://github.com/gcopeland/rf24. I did not compare against the main library since the gcopeland fork outperforms it quite a bit already.

The new library, source code and documentation can be found at https://github.com/TMRh20/RF24. Info in previous blog posts.

More to come...