Improved Mobile Intercom With A6 Module and Arduino Pro Mini

In this instructable I show you how I made an intercom using a GSM module (A6 module) and an Arduino Pro Mini.
If you press the big button, the programmed number is called. The call is ended after a programmed time or if the called phone hangs up.

You can also call this intercom from your phone if your number is programmed in the intercom.

This is an improved version of my first intercom.

See this intructable for the addition of an sound amplifier.

I bought all components on Aliexpress.

A6 module

Arduino Pro Mini (5V 168)

Speaker

Microphone (I found out that these mics work very well with the A6 module, some other electet microphone gave a very bad sound quality)

Button

Box

Perf board etc

I used female pin headers to make the connections in the intercom and to make it easy to remove the modules:

- easy to remove the A6 module tot change the mini SIM card

- easy to remove the Arduino to program it independant from the A6 connections

Connections:

The intercom is powered via the micro USB port of the A6 module

A6 module connections:

VCC to PWR and to VCC of Arduino

GND to GND of Arduino

U_RXD to TX of Arduino

U_TXD to RX of Arduino

REC- and REC+ to speaker

MIC- and MIC+ to speaker

Arduino connections (in addition of the above described connections)

Pin 2: 10K resistor to vcc

Button to pin 2 and ground

Green led to GND and via 220R to pin 4

Blue led to GND and via 220R to pin 5

Pin 8 = debug RX

Pin 9 = debug TX

The Arduino code is on my Github.

The Pro mini is programmed via the Arduino IDE and I standard USB 5V UART programmer.

The default baud rate of the A6 module is 115200 and an Arduino cannot handle this speed via software serial, therefore I used hardware serial for the communication between A6 module and Arduino.
I tried to use a ESP8266 which can handle software serial at a speed of 115200 BAUD, however I did not succeed in getting a stable serial connection at startup.

Important: doe not connect the Pro Mini to the A6 module because it will disturb the programming since the A6 is also connected to the TX and RX pins (hardware serial). Also the A6 module can use the power of your USB port of your computer which can destroy the USB port.

See the comments in the code. If you have questions, do not hesitate to ask me.

Put the mini SIM card in the A6 module (disable the PIN by putting the SIM in your phone and disable it there).

Put the A6 module and the Arduino in the female headers pins.

Drill holes in the box and glue the Leds, speaker and microphone, screw the button.

Connect al components to the right connections.

I 3d-printed two mounts for the box and attached it with hot glue.

Close the box and use it!