Hi Southpark,
What I meant by 0.5 - 1.5 is AC voltage that is present on the speaker while it is ringing.
Please have in mind this is "simple" door Interphone. I am aware there are various Interphone systems and signals are different.
I have done quick and dirty "hack" to just test my code, arduino and toys I got with arduino kit.
What I need is to sense voltage on Interphone speaker. Voltage is present at the speaker only when Interphone is ringing so there is no special cases.
Because it is AC signal Arduino will detect only positive site of a wave. This is okay if I do.
if( analogRead(A1) > 0 ) just once and then open the door delay(n) timeand I am happy that this works as intended.
Now the logic for "advanced" sensing is what I lack.
Because it is AC I cannot count time of ringing simply with START STOP variables. Because if I measure that with just analogRead(A1) my stop will be immediatelly after the signal goes into negative side.
I think that I should measure.
If at least once in eg. millis(20) there is positive peak.
That way I can tell Arduino that the doorbell is still ringing.
Then, I need to note the time of FIRST positive peak and the last positive peak in this 3 second period.
That way I can calculate that I actually rang for the N seconds duration.
This is where I am stuck.
No code is needed for help. Just a general direction how should I do this.
I beleive that this thread is solution for me.