Thread: FM Transmitter Mod
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YoDude is offline YoDude
2010-04-04 , 23:42
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#59
Originally Posted by mzanetti View Post
Yay! Got it!

According to the drivers documentation found on http://www.mjmwired.net/kernel/Docum...nux/si4713.txt the transmitters lower range is 76 MHz. However, the limit on mine is set to 87.5 MHz. I guess this depends on where you bought the device as 87.5 is also the lower limit here in Germany.

You can check the limits on your device/region by executing
Code:
cat /sys/class/i2c-adapter/i2c-2/2-0063/region_bottom_frequency
The transmitters properties (such as the current frequency) can be changed using a tool called v4l2-ctl. I have found a binary compiled for the N900 in this thread:
http://talk.maemo.org/showthread.php?t=46427
Go there, download and install the provided package (lfocus).

After installing lfocus you should have the tool v4l2-ctl installed in /usr/share/lfocus/v4l2-ctl.

Now start your FM transmitter. v4l2-ctl will work only while the transmitter is on.

Set the frequency by executing the following command as root:
Code:
/usr/share/lfocus/v4l2-ctl -d /dev/radio0 -f 87.5
This will set the frequency to 87.5 MHz. Change the value to your desire within the valid range.

PLEASE INFORM YOURSELF ABOUT THE LOCAL REGULATIONS FOR FM TRANSMITTERS AND MAKE SURE THAT YOU DO NOT VIOLATE THEM!!!

Optionally you can change fm-boost to switch frequency every time by adding the above command in the file /sbin/fm-boost. Make sure you insert it after the "#!/bin/sh" and before "exit 0"

Here is an example of mine:
Code:
#!/bin/sh
/bin/echo 120 > /sys/class/i2c-adapter/i2c-2/2-0063/power_level
/usr/share/lfocus/v4l2-ctl -d /dev/radio0 -f 87.5
exit 0
If you are using simple-fmtx-widget and have set it up to execute fm-boost you can now turn on your fm transmitter and immediately tune it down by just tapping the widget.

Have fun!
You da man!
...and why yes, I am having fun.

Just so everyone is clear on this, Installing lfocus with the v4l2-ctl tool will not magically add lower station indicators to the FM transmit tuner.

It will however, allow V4l2-ctl to change the frequency via the command line. In fact, when it makes this change you won't see any difference in the tuner. If the last frequency you had it tuned to was 106.5, it will still show 106.5. However, the N900 will now be transmitting at the frequency specified by the command you or your script entered..

The ideal set up would be to change the FM-Boost script and add the command line to it as shown in mzanetti's post.

I did this and don't even mess with ifocus or the command line once ifocus was installed. Just plug in your charger, fire up Media player, tune to 87.9 in your car, make sure FM transmitter is enabled, and then push the FM-Boost button on the desktop.
BAM! Wall to wall sound dude.

In the US the 87.5 frequency has been reassigned by the FCC for digital TV broadcasting. 87.7 is the DTV buffer frequency and 87.9 would be the FM radio buffer frequency. As a result of this reassignment, newer radios and the N900 do not tune below 88.0 as built.

So IMHO, (I am not a lawyer, nor do I play one on TV.) if you are going to use one of these reassigned frequencies, be a good neighbor and stay out of the assigned DTV freq. of 87.5. If you stick with 87.9 and there are men in black driving the highways in vans with antennas sticking out of them like porcupines, the squawk they here as they drive by your set-up could be construed as just FM frequency bleed and not some one intentionally jamming an FCC assigned channel.

Edit: Through some more reading I now believe 87.9 is still an assigned FM frequency... No one uses it commercially because now most new car tuners won't go below 88.0.
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Last edited by YoDude; 2010-05-14 at 01:13.
 

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