Simple LM386/BC547 indoor-outdoor intercom panel.

Here is a simple one-way intercom circuit using the LM386 integrated circuit.

I've used the schematic below to make to a one way intercom.

Two-way intercom.

You can turn it in a two-way intercom by using the DPDT switch. The speaker works both as a MIC and speaker.

The transistor I used for the
 intercom circuit is a BC547.

Or you could make another one like the first circuit without the switch. 

Connection to wall wires.

You might want to connect this circuit to your existing outdoor intercom panel. And this where things get a little tricky.

The way I understand it there is already an amp in the outdoor panel from which the indoor wall wires come from. 

Connecting a Lm386 amp with the wall wires seemed to work for me. It gives more amplification.

If I just connect a speaker directly to the wall wires it still works but I need to bring the speaker close to my ear to hear anything.

But I still need and amp for the outgoing audio from the indoor wall wires to the MIC in the outdoor panel.

The wire colors coming from the wall are not standard. Mine are:

Red-Common

Blue-Audio in

Grey-Audio out

Yellow-ring

Light blue-door unlock

This is how I connected the wires to my circuit and it worked.

I connected the red wire (common) to the audio in (+) coming from the wall. The microfone is in the outdoor panel. You don't need to add it.

The Blue wire (Audio in) to the audio in (-) and it worked just fine.

The LM386 intercom without preamp.

You should omit the MIC in the circuit above because it is already in the outdoor panel.

You could add a 5k variable resistor and then a 10uF capacitor in series from pin 1 to pin 8 for adjustable gain.

The 10k variable resistor in the input is volume.

Outcoming audio to outdoor panel.

The circuit above is for the indoor speaker for the incoming audio.

Now about the outcoming audio.

For the outcoming audio I have just connected a microfone to the wall wires.

Audio + to the common wire (red in my case).

Audio - to the audio out wire (grey in my case).

The rest of the circuit already exists in the outdoor panel. 

If you hear nothing then make another amplifier like this for the outcoming audio.

Intercom buzz

There is a constant noise coming out of the speaker. Probably due to ground loop or the 9volt battery or bad wiring . Or there could be a problem in the outdoor panel which I'm not willing to touch since  the apartment is not mine.

That can be improved with better wiring ,shorter wires except for the speaker ,star ground (all grounds connected to a single spot, twisted input wires with shielding if possible and a 9-12v adapter instead of a battery.

Maybe the problem lies in the outdoor panel transformer giving out noise.