Richard Corfield (M0RJC)
Measuring the input to the "Carrier Detect" circuit on the FoxTrak APRS tracker
Input was the audio out from the netbook. The AC signal is quite reduced by the time it gets to the microcontroller. It is added to a DC bias set by RV2. Mine is set to just under 1.5V.
A technique for setting RV2 is to increase the bias voltage while playing music into Pin 5 of the radio connector. Don't start too low or you'll short out your music player. When the "CD" LED comes on stop increasing and stop the music. The CD light should go out after a couple of seconds. Then start the music again and see that it comes on.
You can measure the bias on Pin 10 of the PIC or Pin 2 of the radio connector. The picture shows measuring using a Picoscope PC oscilloscope on Pin 10 of the PIC.
DK7IN has some interesting notes on this at www.dk7in.de/TinyTrak_e.html
I reckon a simple circuit can decode the signal, something I'm working on in software simulation at the moment and fingers crossed could try in hardware.
Measuring the input to the "Carrier Detect" circuit on the FoxTrak APRS tracker
Input was the audio out from the netbook. The AC signal is quite reduced by the time it gets to the microcontroller. It is added to a DC bias set by RV2. Mine is set to just under 1.5V.
A technique for setting RV2 is to increase the bias voltage while playing music into Pin 5 of the radio connector. Don't start too low or you'll short out your music player. When the "CD" LED comes on stop increasing and stop the music. The CD light should go out after a couple of seconds. Then start the music again and see that it comes on.
You can measure the bias on Pin 10 of the PIC or Pin 2 of the radio connector. The picture shows measuring using a Picoscope PC oscilloscope on Pin 10 of the PIC.
DK7IN has some interesting notes on this at www.dk7in.de/TinyTrak_e.html
I reckon a simple circuit can decode the signal, something I'm working on in software simulation at the moment and fingers crossed could try in hardware.