Detecting Pressed Call Button on Video Intercom with ESP8266

Hi,


DOMOFON
1. video
2. VCC
3. GND
4. chime (4.5v) - short-circuits to ground when pressed.

I'm looking for hints on how best to solve the status detection problem.
I have a video intercom where 4 wires go. I wanted to detect pressing the bell and sending data over the mqtt further. I found 2 wires that short together when someone presses the bell only question arises.

I want to detect this from another chip (ESP8266), on 2 of these wires I have 4.5v with a multimeter I measured that the button simply short circuits the state line to GND.
What is the best way to detect a low state from an Arduino or similar?
I have a couple of ideas.
- transistor on the line esp
- measuring the voltage on the line analogue
- a common ground and a resistor to check the high state.

Please direct me on the right track.

Optocoupler. There is probably also an audio signal on 4 and shorting it to anything will distort the conversation. Additionally, there will be full galvanic isolation between the devices.

If the button is short-circuiting to ground and sound is flowing through there during a conversation, it is a good idea to detect the button press with a circuit with a high input impedance and a low-pass filter (which does not pass sound) at the input. You have an example of a mosfet solution here:

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simulation .

Since the audio signal goes to circuit ground (?) when the button is pressed, it will also go to the emitter of the transistor and thus interfere with the voltage measurement by the ESP, whose input in Input mode has an impedance of about 10 MΩ.

Added after 15 [minutes]:

MEN8989 wrote:

I want to detect this from another circuit (ESP8266), on 2 of these wires I have 4.5v with a multimeter I measured

.
From the 4.5v you will not be able to power the ESP directly, which requires a 3V3 supply.