FM radio receiver
#1
Hello

I know that the PinePhone doesn't have the hability to receive FM radio natively.
I am wondering if this is something that could be done using the pogo pins.

What I have in mind is something like a case with dedicated hardware to decode and then send the signal to the phone via I2C.

Note that I have no experience in hardware thinkering. This is just a thought.
#2
Hmm. Isn't the cellular/WiFi transceiver in the PinePhone an SDR? Isn't this the only reason other manufacturers have included FM band reception? If so, couldn't it be programmed to receive that band? (And other such bands)

If not, find yourself a really small FM receiver of your choosing, and glue it to the back of the phone. That's simpler than integrating new hardware into the phone.
#3
There is actually a FM receiver in the Wifi chip - but I don't think any drivers for it exists.
#4
(07-26-2020, 09:42 PM)KC9UDX Wrote: Hmm. Isn't the cellular/WiFi transceiver in the PinePhone an SDR? Isn't this the only reason other manufacturers have included FM band reception? If so, couldn't it be programmed to receive that band? (And other such bands)

If not, find yourself a really small FM receiver of your choosing, and glue it to the back of the phone. That's simpler than integrating new hardware into the phone.

The cellular and wifi transceivers in the Pinephone are entirely separate devices; the wifi chip is a Realtek RTL8723CS chip which connects via SDIO, while the cellular modem is a self-contained blackbox that connects via serial over USB (it's the metal-shielded EG25 module visible with the back cover removed). The modem's firmware is highly proprietary and assumed by many to be some combination of hostile and insecure, which is why it's treated with so much careful isolation in the Pinephone's design. In addition, the FCC mandates that all cellular devices like this have signed firmware that cannot be tampered with by the end user, so even if we reverse-engineered it, we couldn't modify it. Many mobile phone processors (almost all of them, actually; Qualcomm's Snapdragon line is a big one) have cellular baseband built into them, meaning that the whole chip is required to run signed code and is thus pretty much useless to open-source projects. The Pinephone's separation of system and baseband is one of its primary features.

Either of the wireless chips could be SDRs at some level, but thanks to intellectual property territorial disputes in the industry and a bunch of regulatory stuff, we'll probably never be able to hack them like this. At the very least, the vendors - and the FCC - are trying very hard to stop us.

Side note: reverse-engineering efforts on wireless chips have been successful in the past, like with the Nexmon project that managed to get arbitrary transmit capability on the BCM43455 wifi chip found in some phones and Raspberry Pi boards. Unfortunately, last time I checked, they never managed to get receiver capability working, and the project seems to have fallen dormant.

As for FM radio reception, it's true that many wireless chips have built-in FM receiver functionality, but for whatever reason, there never seems to be any kind of support for it in the drivers. I guess it's just not profitable enough to bother adding it nowadays. It would be cool to see a reverse-engineering effort to bring it back, but for now, it seems to be a lost functionality.

I would be interested in finding out if the I2C bus on the Pinephone's pogo pins has enough bandwidth to carry listenable audio. If so, adding various forms of additional radio connectivity could be a neat project.
#5
I will maybe try to do something once I get a PinePhone and some time.
#6
https://wiki.seeedstudio.com/Grove-I2C_FM_Receiver/

The i2c is there for control, not for transferring audio, and the headphones double as the antenna. It shouldn't affect battery life too much. If you want to get audio data into the phone you'd be better off using bluetooth or usb - rtl-sdr perhaps?
#7
The WiFi / BT chip has an FM radio receiver function clearly visible on the spec sheet.  Doesn't look like there was anywhere to route the audio it produces into the Allwinner SoC so none of those pins are connected.  You need either an analog or a digital audio channel and an i2c link, plus wiring the headphone's ground wire as an antenna input.  Modifying the board for all that ain't happening, especially since there isn't anywhere to send the audio anyway.

Because of the antenna requirement you would end up with a second headphone jack for the add on back plate, but other than that there isn't any real obstacle to making such a thing.  You have an i2c link on the pogo pins along with sufficient access to power.  Since it would need to be thick enough to have a second headphone jack you would have plenty of room to stuff some other goodies in, perhaps more battery?


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