FAQ: Wireless audio streaming via WiFi/Bluetooth (With mod demo!)

[Hamberthm]

As there’s a lot of people asking about this, I decided to concentrate here all the info I gathered about this topic, what is possible and what is not.
BEWARE: This info applies to ATS-MINI style receivers of the V1/V2 revisions and the AMNVOLT V1, V2 and V3. Further chip redesigns might introduce new features that could make this info obsolete.

TL;DR / In a nutshell

• Without hardware mods: Not possible.
• Bluetooth: Not possible ATM.
• WiFi: Very low sample rate, high noise, mono, needs a trace cut and two wires soldered. Instructions down below.
• Adding codec chipsets: Unexplored, this is advanced modding beyond the receiver’s design and, of course, anything is possible by adding components.

Explanation: Audio connection to the ESP32S3

There is no connection between the audio output of the SI4732 radio chipset and the ESP32S3 main processing unit. There’s only I²C bus communication between both chips and this is only used for issuing control commands to the radio chip, like changing freqs.
The SI4732 has the capability to output audio in normal analog stereo modulation, or via some digital modes like I²S.
Connecting I²S or Inter-IC Sound, is not possible. The SI4732 has the option of an external clock reference, or an internal oscillator mode. When in internal mode, it requires the addition of an external crystal, which is connected using one of the pins that carries the I²S protocol if activated (GPO3/DCLK pin 2). The ATS-MINI uses the internal osc mode, therefore no digital audio option is possible due to pin 2 being used for the crystal.
Only analog feed is achievable via a (relatively) simple mod, as I will explain further below. For this, one of the Analog to Digital converter inputs of the ESP32S3 must be used. The ESP32S3 has 2 ADC units, called ADC1 and ADC2, and both have up to 10 input pins, or “channels”.

The use of ADC2 would be desirable because the design of ATS-MINI left free/unused pins only for ADC2 channels, but this is not possible for these reasons:

• ADC2 is also used by the WiFi firmware module and is known to cause problems and instability in continuous sampling mode, needed to sample the audio. Only one-shot RTC sampling is possible which is not suitable for audio sampling.
• ADC2 continuous mode is UNSUPPORTED by ESPRESSIF, the manufacturer of the chip, due to chip design flaws (check official errata) and library support is disabled by default in the ESP Core for Arduino IDE and cannot be activated without recompiling the core, which is troublesome for most DIYers. It can only be force-activated in ESP-IDF compiling environment and that would need a total project migration, also unpractical.

Only ADC1 is left as an option and this requires a further challenge, because no free ADC1 pin is left on the ATS-MINI design. The only simple way is to relocate the battery voltage sensing to an ADC2 pin, because it is done via one-shot sampling, and that would leave us with GPIO4/ADC1_Ch3 pin for use to sample audio. Check below for the explanation.

Explanation: Audio streaming from the ESP32S3

Bluetooth audio is not possible at the moment, because the ESP32S3 wonderful and futuristic (and cost cutting!) feature-set left us with NO Bluetooth Classic support. Between the features of BT Classic, there’s the A2DP audio streaming profile that is what powers all the Bluetooth speakers/headphones/music-emitting-whatever of the world. We only have the newest BLE, or Bluetooth Low Energy on this chip. There’s of course a new profile called BLE Audio but its adoption is yet to be widespread; there are circa none BLE Audio products like speakers, and there are no libraries nor official support from ESPRESSIF to use the protocol on the chip. Even if ESPRESSIF releases the library tomorrow, it would cost you a little fortune to buy a compatible device to use it, as they are yet too novel.
The other wireless capability of the ESP32 is of course WiFi. The easiest way to do it is to use the already implemented webserver on the ATS-MINI project and do streaming on another port, so you can listen in a web browser. This is the only thing that has being done by me and is explained below.

The only possible and relatively easy mod

This will only get us LOW SAMPLE RATE and HIGH NOISE audio because the ADC modules on an ESP32 are not suitable for audio sampling. This is ONLY useful for voice broadcasts.
As we can’t use ADC2, we’ll use the ADC1 module of the ESP32, as explained above. For this, we need to get a pin free because all of the ADC1 ones are in use. The only candidate is GPIO4 which does the battery voltage sampling to calculate the battery level on screen, and this can be relocated to a free ADC2 pin as we can use it to recover it’s function.

PROCEDURE:

1- Cut the trace going to GPIO4 (BAT_ADC) to effectively disconnect it from the pin, using a sharp point knife. Before continuing, turn on the radio and use a multimeter to verify there’s no longer a voltage present at this pin (is usually 2 volts or so on normal conditions).
2- Solder a jumper wire between PIN 8 of the NS4160 amplifier chip (VOP pin) to the recently freed PIN 4 on the ESP32S3 (GPIO4/ADC1).
3- To recover battery status functionality, solder a jumper wire between BAT_ADC point (R8, R10 or C12) to PIN 19 on the ESP32S3 (GPIO11/ADC2).

Now you need to make modifications to the firmware:

1- Use Arduino Audio Tools library to sample ADC1 channel 3 in continuous mode.
2- Start a webstream on another port, like port 81.
3- Reconfigure BAT_ADC pin on the firmware to GPIO11.

I can provide such modifications but you’ll have to wait another week or two, as I’m currently without my ATS-MINI, I’ve got a broken screen.

DEMO VIDEO

https://youtube.com/shorts/P2JalmDXG0s

Well, I hope this answers all the questions regarding wireless audio on our beloved receiver, and makes good and interesting reading for some people.

Cheers!
Humberto

[G8PTN]

Hi Humberto,
Thank you for the great summary. A couple of comments.

• The firmware with the CW/RTTY decoder uses one of the spare pins on the ESP32-S3 module, IO11 which is associated with an ADC2. Perhaps WIFI is not being used in this case, or the sampling rate is lower.

• Theoretically, it would be possible to get access to DLCK on the SI4732-A10.

  I tried an experimental build using the LEDC block in the ESP32-S3 to generate a 32.768 kHz clock with the fractional divider, and fed it out on one of the spare IO pins to the RCLK input as the external clock.

  

  This has some drawbacks, because of potential noise generated from the clock signal, although I did slew limit the signal with a 2k2 series resistor.

  It may be possible to use a small DS3231 module (with battery), which has an integrated TCXO, and can generate an accurate 32.768 kHz clock, stable to within a few ppm. This would also provide a real time clock for the ATS-MINI via I2C.

  

  With an external RCLK, it frees up the I2S signals to be used, but unfortunately, I have read on some of the forums that the SI4732-A10 does not appear to work in I2S mode, only the SI4735-D60.

Additional notes on the DS3231:
There are two versions of the DS3231, one is marked “DS3231SN” and the other “DS3231M”.
The device marked “DS3231SN” has a temperature compensated TCXO and outputs an accurate 32.768 kHz signal.
The device marked "DS3231M" is an accurate RTC, but the 32.768 kHz output is only accurate to within +/ 2.5%.
Also, the "DS3231SN" can output different frequencies on the INT#/SQW pin, 1 Hz, 1.024 kHz, 4.096 kHz and 8.192 kHz, which is not possible on the "DS3231M", which can only output 1 Hz.

73, Dave