lowering the DC voltage on a circuit programmatically

[ClockToshi]

I have an intercom that is based on a two wire system with DC 28 V It's an elvox duefili.

With an esp32 + adc and a voltage divider I was able to sample the voltage. upon ringing the doorbell and opening the gate I can see the different voltage drop. I can also "see" my voice on a plot of the sample if I speak into the intercom phone microphone.

I can now detect when someone rings the doorbell and I can send a notification as needed.

I would like to extract the audio (I believe it is mixed with video) and I would also like to at the very minimum trigger the gate open but even better talk into the intercom (i'm a bit familiar with esp adf)

what other hardware do i need to lower the voltage with precise timing to at least open the gate or even better encode the voice as voltage changes.

My understanding is that I need a solid state relay and some DAC pr LEDC controllable load, but i am not sure about what really would fit the use case. Maybe it's none of that and something else entirely

Thank you

[ESP_Sprite]

The original hardware probably simply connects a resistor over the two wires. If you know what resistance that is (either by reverse engineering the original unit, or by simply trying) you can use a mosfet to switch that resistance on or off as well. For the voice, it's likely AC-coupled onto the line: imagine an audio amplifier with its output connected to the positive line via a capacitor.