APRS tracker with Arduino Duemilanove

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#1
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Hi,
I'd like to share a project to implement an APRS tracker using an Arduino 2009.

This device can be used to periodically send a message through a radio AFSK channel and log the received messages to a serial port (UART).

You can find complete source code and schematics on the project's home page.

Feel free to extend it and share comments! :)

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Hello lucaotta,

Interesting project, have you developed the AFSK part yourself or is it taken from another project? Can please explain how your demodulation algorithm works.

Is it possible to use it with an APRS software like UI-View?

Kind regards,

Gilles

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roodemol wrote:
Hello lucaotta,

Interesting project, have you developed the AFSK part yourself or is it taken from another project? Can please explain how your demodulation algorithm works.

The algorithm has been developed from AFSK specifications, no external libraries involved.

As for demodulation, you can find general information on the Wikipedia page.

The demodulator samples the signal at 9600Hz.
The samples are sent to a delay line of 4 sample.

The demodulation is achieved by multiplying the current sample with a
sample delayed of half bit.
In this way we get a signal which is positive when the bit is 1 and
negative when it's 0. There is however an high frequency component in
this signal. So the signal is then low-pass filtered (600Hz) to leave
only the bits information.

Then the bit stream must be demodulated again since the bits are
manchester encoded (NZRI actually).

roodemol wrote:

Is it possible to use it with an APRS software like UI-View?

Sorry, I don't know the software you mention.
If it can parse string serial input, you can modify the function message_callback() to customize the output.

Hope this helps.

Luca