RDS/RBDS FM receiver (external) for traffic conditions

Doug Sutherland doug at proficio.ca
Sun Nov 18 19:45:18 CET 2007

> A USB audio device does appear when it's plugged in.
> However, there is no audio until the FM radio app is run.
> This does SPI communication with the SI4701 to init
> and change its settings.

Yikes that was a poor description. Let me try that again.
There is a micrcontroller onboard the USB FM radio
stick along with the SI4701 receiver. The microcontroller
provides the USB interface and does SPI communication
with the SI4701. Plugging in the USB stick creates a
composite USB device, both audio and generic HID.
Nothing happens until the FM radio application is run
on the PC. This sends some init commands to the
microcontroller which in turn sends init commands to
the SI4701 over SPI. Then the radio starts working.
I have not seen any RDS/RBDS capability with this
FM radio stick. It is likely capable, assuming it has
SI4701 (not SI4700) onboard, but you would need
to be able to flash the microcontroller code with new
code for that capability (I think ...)

  -- Doug

> > They claim it uses standard USBaudio for the sound and that they use the
> > HID spec for control interface (which doesn't make a ton of sense to me,
> > as it seems backwards, but I have not reviewed the spec).
> Why would this be backwards?
> HID is human interface, which in this case is buttons on the FM radio
> GUI application, you have a stereo/mono select, volume slider, mute
> up and down frequency tune and scan buttons, a button for configuring the
> preset stations, and buttons for preset stations. What is backwards about
> this? Audio is standard USB audio, controls are custom "generic USB HID".
> > This is also the FM chip used in the M$ Zune, but there doesn't appear
> > to have been a lot of progress made on the linux front there.
> I haven't looked at the code for the FM radio application, and have no
> idea about making this existing application work with linux. There is
> other source code also for the evaluation board for the chips.
> The FM radio stick doesn't appear to demo any RDS/RBDS capability,
> at least not where I am, no station or artist/song names are appearing.
>   -- Doug
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