FM radio reception on neo/openmoko and some other questions

Doug Sutherland doug at
Sat Nov 10 16:36:14 CET 2007

Georg wrote:
> no only in terms of speakerphone, also the navigational software (as far 
> as there'll be one) may be connected through it.. There are a lot of 
> possible ways to use that extension and I personally think that it's a 
> very useful additional feature .

The supplier where I usually buy parts has only the FM receivers in
stock, but the interesting thing is that these went way down in price
just in the past couple of months. The SI4701 with RDS/RDBS is
$5.22 single qty, I paid over $18 for this same part from the same 
supplier in September! Back then the SI4700 (without RDS/RDBS)
was roughly half the price, now it is $4.55. At quantuty 100 this 
part goes down to $3.03, not bad for a complete FM receiver.
The price of the development board also dropped down to $125
and the USB FM radio stick demo is $35. But this distributor
(Digiykey) only has the FM receivers, not the AM/FM receivers,
FM transmitters, or FM transceivers.

Another distributor Mouser also only has the receivers. They have
an evaluation board for SI4713 transmittable orderable but not in  
stock and yet they don't list the chip itself. 

NuHorizons has these in stock:

SI4710  FM Transmitter $10.35
SI4711  FM Transmitter with RDS/RBDS  $12.43
SI4712  FM Transceiver $11.96
SI4713  FM Transceiver with RDS/RBDS  $14.35 
SI4730  AM/FM Receiver $14.87 
SI4731  AM/FM Receiver with RDS/RBDS $16.89

So assuming RDS/RDBS capable versions ...
FM receiver $5.22 from Digikey (SI4701)
FM transceiver $14.35 from NuHorizons (SI4713)
AM/FM receiver $16.89 from NuHorizons (SI4731) 

The SI4701 FM receiver has analog audio output so it could
connect direct to audio input, or could also be converted to 
USB audio using PCM2900 or similar. The SPI port is for 
control (scan frequencies) and receiving RDS/RBDS. If it was
done as USB, with a 2-port USB hub chip, PCM29xx USB
audio, and small USB microcontroller with SPI (and driver
for virtual USB UART), this could plug into the USB host 

The audio interfaces are simple but the control interfaces may
be a bit of a challenge for integration with Neo, if you want 
control from the phone itself. Alternatively, a simple FM 
receiver could just have a scan button on the receiver board
and only an analog interface to Neo. 

Regarding transmitters and transceivers, I need to look closer
at those. One of the other things about these is you basically 
need to buy a development board to even get full datasheet.

  -- Doug

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