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Author Topic: Hamradio and APRS mobile tracking with gps  (Read 1816 times)
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Hello everyone,

I begin in the discovery of the arduino (for now I just read, with nothing purchased to date) and would like your opinion on the feasibility of beginning a project which I fail to find of similar schemes.
Indeed, I have a Garmin eTrex H (Yellow :-) with serial port. I can get into this unit new waypoints with compatible software on my PC without having to validate from the gps ... and tell me so it should be "easily" possible  to extract a callsign from a "Baycom module" and view its distance and heading on my gps.
What do you think ?
(more simply still "my" program to extract a string and inject it into the GPS could be added to an existing code capable of decoding the frames on my VHF APRS heard ? )

Thank you for your opinion !

... and although I have not found anything that looks like this project ... Perhaps you already have links :-)


Tete
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If you have a Baycom modem that outputs serial, and a GPS that inputs serial, it shouldn't be hard (famous last words) to get them talking to each other through an Arduino. You'd need to use software serial for at least one of them, and probably the hardware serial for the other - probably hardware serial for the Baycom since you don't know when signals will come in.

If you have a USB Baycom modem, that's significantly harder.
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Hello everyone,
and thanks AndyCC for your return :-)

Ok for those definitions (software and hardware serials) that already allow me to focus more easily in the bibliography.

(I am in the case of a serial Baycom :  an old installation with a tcm3105 ... that might revive as a shield :-)

... and unless the modem is useless because the arduino know directly decode the audio frames from leaving the vhf ?

tete
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I don't think the Arduino has enough processing power to decode AX.25 from a radio directly. You'd need to sample high-resolution sound, store it, then translate that into AX.25 - all in 2k of RAM and a 16MHz processor. That would be almost impossible.

You'll need something to turn the AX.25 into serial data before it gets to the Arduino.
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Ok AndyCC, thanks again :-)

> You'll need something to turn the AX.25 into serial data before it gets to the Arduino.

While surfing I found this link :
http://shieldlist.org/argent/radio

...  this morning I have found this URL :
http://sites.google.com/site/ki4mcw/Home/arduino-tnc
But, for this last link,  I'm not sure I understood everything (I do not control English, far from it :-(

... and wonder whether it would be wise (financially and also for not accumulate complications for a beginner) to choose the solution of tcm3105 (my old Baycom) ?

Tete
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AX.25 decoding has been done.  One example is the WhereAVR, which uses an ATmega8 and even parses simple APRS messages for command and control.

The magic phrase to google is "zero crossing detector". Watching for the AC audio signal to cross the zero point turns the signal into a digital square wave. It typically isn't as effective as using an analog modem Ic (e.g. MX614, or the TCM you mention), but it is simpler and cheaper to build and some folks give those a higher priority than performance.

-j
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