SKS Bus

[AzonInc]

I have an intercom by SKS Kinkel and reverse engineered their bus to be very similar. The audio is superimposed onto the 19-28 VDC baseline. The control messages are using FSK (Frequency Shift Keying), so basically sending two different tones for 0 and 1 instead of just dropping the voltage.
I would love to get my hands on a Doorman with audio functionality that I could use to implement the protocol for ESPHome.

Originally posted by @kroimon in #5 (comment)

[AzonInc]

The v2 core board is designed to still only handle voltage drop based bus systems like the TCS/Koch TC Bus or Siedle In Home Bus.

The audio extension is using the es8388 and will provide digital i2s audio data to the ESP32S3.

How would you access the data in there?

[kroimon]

My naive approach would be to run the audio input data coming from the ES8388's ADC through the Goertzel algorithm to detect the two distinct frequencies making up the symbols. Sending data would also be possible by using the DAC on the ES8388.

Some quick notes I made when analyzing the protocol:

SKS Kinkel Audio Bus uses Binary Frequency-shift keying (FSK) on the a+/b- lines with an amplitude of 2 V, superimposed on the 19-28 V base voltage:

Symbol L = 1.5ms @ 18.3 kHz
Symbol H = 1.5ms @ 22.8 kHz

3 Symbols per Bit:
Bit 0 = LHL
Bit 1 = LHH

222.2 bits/s
Each transmission consists of 16 bits (48 symbols):
1 peak (noise?), 15 ms pause, 15 ms H sync pulse, 48 x 1.5 ms per symbol

Complete transmission:

Symbol H:

Symbol L:

[jsschmid]

@kroimon Do you have a capture you could provide so I can run some tests on it? A friend of mine has a SKS door station, but I'd rather not open it if not necessary...
And please, could you elaborate which SKS device it is that we're talking about here?

[kroimon]

What do you mean by capture? Which format would help you?
I have the package data pretty much figured out at this point.

[jsschmid]

What do you mean by capture? Which format would help you? I have the package data pretty much figured out at this point.

Excuse my late reply please.
What I meant is the data in a captured format which would allow to replay the data to a doorstation e.g. to invoke certain functionalities.

[kroimon]

No, sorry. I really only have some captures from my oscilloscope, nothing that can easily be replayed. Also, you would need the correct hardware for that anyway.

When I find some time, I will write up and post my findings about the protocol messages.