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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.
Isn't it expected that, by the third year, you should have at least some clue...?
Yes, it is possible.
As far as the GSM modem is concerned, it neither knows nor cares where its audio input signal comes from - just so long as it meets the input specifications. Just make sure that the particular "modem" does have an audio input - ie, it isn't just a data-only modem!
Dialling the call is just a matter of issuing the appropriate AT Commands.
Note that some modems can embed an application within the modem - so you might not need an external microcontroller at all!
http://www.wavecom.com/openat www.telit.com/.../gsm-gprs.php etc, etc,...
There are chips available to do speech synthesis; There are chips available to do text-to-speech; There are chips available to store & play-back sampled audio; Or you could just store the data in a microcontroller, and use simple PWM to convert it to analogue audio.
I would like to see your research. If you think I am aloud.
Andy, yes at third year they might expect us to have some clues. But when I looked at the forum I realised that even experienced professionals still ask questions of this level, and most of them are way much simpler than the one I'm asking.
Thanks for the links you sent me. The problem still is that I can't seem to get hold of a chip that can store wave files, and if I were to find it, none of the GSM modems that I came across from the many different vendors have AT commands to read an audio file and play it back. Please guide me.
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.
"none of the GSM modems that I came across from the many different vendors have AT commands to read an audio file and play it back"
Read my post again: you would have to generate an analogue audio signal, and feed it to the modem's analogue audio input; the AT commands would just be for dialling the call...
"a chip that can store wave files"
Stop thinking about "wave files"; just think about data - digital samples of an analogue signal. There are lots of chips that can store data...
Or you could interface an SD Card or similar to your microcontroller - and read WAV files from it...