[Gta04-owner] FM Transceiver - split frequency?

Andreas Kemnade andreas at kemnade.info
Mon Apr 9 20:20:41 CEST 2012


On Mon, 2012-04-09 at 19:04 +0200, Christ van Willegen wrote:
> Hello,
> I was wondering if the FM transceiver was a split-frequency receiver/sender?
> If so, it would be possible to tune to an FN station, 'overlay' system
> audio over it and transmit it to a (car) FM receiver on another
> frequency. That way, you can overlay voice navigation, messages, read
> SMS messages, you name it...
> But is that possible with the hardware?
At least using it that way is not documented. There is something
like this in the docu:"Write xx to register yy to put it into transmit
mode" and "Write xx to register yy to put it into receive mode"
So I guess no.

But there are also usb-sticks containing that kind of chip so maybe
that is a solution. The transmitter needs also a separate antenna. 
There is no one in the gta04. I have not tried connecting one and
using the si4721 as a transmitter.

About the driver. the status is:
I can play audio data into the si4721. It arrives at the right pin.
Clock comes from the SoC and looks sane. 

When I try to record things from the si4721,
I also have clock signals from the SoC and the si4721
gives out data at the right pin but programs like arecord
do not spit out data.

Andreas Kemnade

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