Initial Testing, Notes & Progress on new PCB for Wireless Audio Prototyping

 Initial Testing, Notes & Progress on new PCB for Wireless Audio Prototyping

 Testing out the new circuit boards and getting the built-in microphone working

 If you weren't following along I just received some new custom built circuit boards from PCBWay.com and have been testing things out extensively. Everything works! I even got the custom-added I2S microphone working with the nRF52840.

The boards support functionality like voice transmission over the built-in radio, and can function as a radio, intercom or simple music player etc. 

                                            A full test of the new circuit boards

Getting the Microphone working with the AutoAnalogAudio library: 

The nRF52840 Feather Express/Sense does have an I2S interface, but it only supports up to a 24-bit window, whereas the SPH0645LM4H expects 32 SCK pulses per audio frame (18 bits of data + 14 bits of padding) and a 64 x BCK signal, where the nRF52840 typically does a 48 x BCK signal.

After a bit of searching, I found that the appropriate signal could be created by the PWM peripheral of the 52840, and the I2S interface would just need to be configured with special settings to grab the 18-bits of data properly.

The main drawback with using this mode is the I2S interface can only operate in either Input or Output mode, they can't be run at the same time unless both I2S Input & Output devices use the same settings. I had to make some modifications to the AutoAnalogAudio library, released in v1.54.0, in order to allow switching between I2S modes.

Currently, this mode is only supported for input devices. 

                                                                The Feather Express 52840 

Configuration for the Microphone: 

To use the new special settings, users need to set the aaAudio.manualI2S variable to True before calling the aaAudio.begin(2,0); function.

With the Feather Express, the LRCK or WS pin needs to be configured from the default of 29, to something like 28, which is A3 on the Feather Express 52840

Results: 

 I've put together a full Radio Transceiver example for this PCB, found at https://github.com/TMRh20/FeatherAudio/tree/main/Examples/I2S_TransmitterAndReceiver

In order to use the example, upload to two Feather 52840 Express or Sense boards, and plug them into the custom PCB, or manually attach external I2S microphone & amplifier.  

The example features 3 buttons, the PTT button is used to transmit, then there are two for Volume Up/Down. If users press and hold Volume Down, then Press Volume Up, the device will go into a continuous transmission mode, not requiring the PTT button to be pressed.

The device also toggles the onboard red LED when data is received.

 Audio is relatively high quality at 16-bits and 32kHz, so it is pretty clear and useful for many different applications.

 

New Circuit Board for Audio Prototyping, Sponsored by PCBWay.com

 New Circuit Board for Audio Prototyping, Sponsored by PCBWay.com

 Design and manufacturing of a custom circuit board

 With recent developments to my AutoAnalogAudio library for Arduino adding support for nRF52840 based devices like the Feather 52840 or XIAO 52840 lines, I was getting a little sick and tired of having a big tangle of wires in order to run an SD card, I2S microphone, I2S amplifier, speaker etc, in order to test things out and develop this library.

Thanks to a sponsorship from PCBWay.com, I was able to develop a custom circuit board for prototyping and development, that can later be used as a walkie-talkie or intercom, with range similar to bluetooth.

The first part of this was to actually create the custom circuit board, and I chose the KiCad application. This was a big learning curve, as I had only ever designed an extremely simple circuit board before, and that was quite a challenge for me. This would take things to the next level.

So first, in KiCad, one needs to create a schematic for the circuit. This part was not too difficult, although it still presented some challenges, and took up a fair bit of time.   

 

 Above is the original circuit design and all the KiCad files etc, are available on https://github.com/TMRh20/FeatherAudio

The people at PCBWay were very helpful in figuring this all out, and since this is what I consider to be my first real attempt at a proper circuit board, I made a number of mistakes. One of the hardest parts seemed to be matching the KiCad component footprints up with the proper part numbers. I assume there must be an easier way to do this, but I ended up searching and searching, and still made some somewhat unrecoverable errors.

Beyond the correctable errors that the folks at PCBWay helped me fix, one of the main mistakes was ordering the wrong part for the J5 connector. This was in addition to a bunch of other parts that I had incorrect, but were caught prior to production. In the end, I had the boards shipped without the J5 connector, but the PCBWay people shipped some connectors that I was able to modify to work, and soldered them on myself.

I was also missing a position file initially, because I didn't know at first, but you need to send three main files, the gerber files in a ZIP format, the Bill of Materials or BOM, and a Position file, all of which can be generated from within KiCad. Putting this all together was one of the hard parts, again I struggled quite a bit with finding the correct part numbers etc.

 

Above are pictures of the PCB itself, and the assembled PCB, missing the J5 connector which I messed up the part number on. Everything else was correct, thanks to a lot of help from PCBWay.com. As stated, I was able to solder on some slightly modified J5 connectors they sent along with the boards.

Upon hooking it up, inserting an SD card and attempting to play some music, the damn thing worked! I was pretty surprised everything actually seemed to be connected correctly, and functioned flawlessly! Upon trying the microphone however, I discovered that I might have selected an I2S microphone that the attached micro-controller (Feather Express 52840 or Feather Sense 52840) cannot quite handle. According to some searches, I may be able to modify my AutoAnalogAudio library to handle it, but as it stands, the built in mic does not function.

 I am still able to do some testing and work with the Feather Sense 52840, because it has a built in PDM microphone, but I was hoping to use the custom-added I2S microphone. Everything seems to be connected properly circuit wise, its just the 52840 MCU that needs what seems to be a special configuration to work with this microphone.

 

 Above is my test setup with all the components attached. The small battery runs the micro-controller, SD Card and microphone, while the large batteries handle the I2S amplifier. I'm still kind of amazed all the circuitry seems to be correct, there is just a compatibility issue with the microphone!

 

 That's all for now, I've posted all the related files and examples to my GitHub repo at https://github.com/TMRh20/FeatherAudio, and will do some follow up posts detailing how to use the AutoAnalogAudio library along with this circuit board. To be continued...