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Hi All,
I am doing a GSM project for my third year, and I am clueless where to begin. Please advice me. The requirements are:
A microcontroller receives a signal from a door sensor. Whenever the signal is received (i.e. door opened), the microcontroller must send a command to the GSM modem, and the GSM modem must initiate a call to some pre-defined number. When the called party answers the call, the GSM modem must play-back a voice that says something like "Door opened". So there must be an audio file stored somewhere and played-back whenever a call is answered.
So my main problem is, how do I use a GSM modem or microcontroller to play-back an audio file? Where do I store this file and retrieve it? Your advice will be highly appreciated.
Think about using an external SPI-controlled flash memory. This would allow you to store a lot of speech messages for a reasonable cost.
Then use PWM to play a phrase to the microphone input of the GSM module - just make sure to get a GSM module that has the analogue section.
If you want to, you could either use a microphone, or connect an ADC channel of the microcontroller to the speaker output of the GSM module. Then you could record new phrases.