RDS/RBDS FM receiver (external) for traffic conditions

Joshua Layne joshua at willowisp.net
Sun Nov 18 20:50:02 CET 2007

Doug Sutherland wrote:
> Josh wrote:
>> I have always thought of HID as using an external device that then 
>> communicates to the computer, this is using a virtual app on the 
>> computer to control an external device - I don't disagree that it is 
>> Human Interface.
> Aside from keyboards and mice, this idea is exactly what generic
> HID is for. I have seen others that do the same. For example 
> audio codec evaluation boards use generic HID communication
> and have volume, balance, fader etc controls in a similar PC app.
> Interestingly though, generic USB HID can also be used as just a 
> simple comminication protocol between host and slave, and can
> do pretty decent throughput.
ok, cool - thanks for the explanation.
> I will look further into this, because I have some of the SI4701
> chips here too, my intention was to write my own SPI code on
> a different micro, so I haven't looked too closely at their source.
> I was thinking about doing something better: using a micro to 
> create a virtual com port, using the driverless USB ACM CDC
> (communication device class), which would be translated to the
> necessary SPI commands on the micro firmware, to control 
> the FM tuner and to read and send the RDS/RBDS data.
> This way you would have generic USB audio and generic 
> USB CDC serial, and you could just open a serial port and
> send commands to change stations and such, and the RDS
> data would just "arrive" at the serial port.
> This assume a different custom small board with SI4701 and
> microcontroller, most likely an ARM7.

wow - that sounds like a pretty cool approach.  Not having those 
engineering skills :) I was looking to more COTS products.  I may pick 
up one of the dongles to just see if I can hack something out with my 
utter lack of C++ expertise.

Please keep the list posted on your progress and let me know if I can be 
of any help.

One of the apparent weaknesses of the Si USB dongles (from my armchair 
research) is the antenna connection - it might be nice to have a mini 
SMA or something (with the standard FM resistance -- 75 Ohms?) that 
would be robust and an adpater cable could be used to car antenna or 
such - of course, in an embedded device, the old 'headphones as antenna 
works well enough, but since this would external anyway, it might make 
more sense to allow for a 'real' antenna.


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