Hi
I have a project idea where I want to interface with my intercom / door phone system. Its a proprietary system developed by SSS Siedle, and there is next to no documentation or research on how these devices work.
I have hooked the incoming wires onto my scope and found that the device likely uses a combination of analogue and digital signals for its operation.
From my understanding the system operates as a serial bus where each flat is connected to each-other, and not directly to the central unit.
When idle the bus sits at 30V. Whenever I submit a command (Unlock front door, or start audio/vide) the signal/bus/incoming lead drops to 0Vmin and creates a square wave signal with 9Vmax. Once "one" the signal returns to 30V (Slightly above 30v the first few ms).
I believe I should be able to interface quite simply with this by using an optocoupler or simply just some resistors as a voltage divider.
The problem however is the audio/video part. From my scoping this seems to be modulated into the 30V (carrier?) signal. Whenever there's video transmitted over the bus I can see a 20MHz sine wave that with about 100mV variation between Vmin and Vmax.
How would I best go forth and read this signal? I do not necessarily need to process it on the Arduino (or ESP* or similar), but I would use the Arduino (Or ESP* or similar) to intercept the signal before passing it on to a computer or wirelessly or something.
Would I need an external 200+MHz ADC (ie. an ST ADC120?) coupled together with a resistor voltage divider or some other smart voltage divider?
Is this at all feasible?
PS: Im no EE and I am likely not familiar with anything that go beyond EE basics.