andybee
Posts: 2
Joined: Sun Apr 27, 2014 8:46 am

FM antenna pin on Pi 3's BCM43438 chip

Tue Mar 01, 2016 10:49 am

I understand from the longer Pi 3 discussion thread that the new BCM43438 chip has the ability to receive FM radio, but the pin isn't connected.

Has anyone done any further digging on this? Is it free-floating - not attached to a pad - or is it to the board, but not attached to an antenna from there?

I'm wondering if it's possible to connect to an antenna and then coax the software in to life.

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4221
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: FM pin on Pi 3

Tue Mar 01, 2016 10:52 am

It was mentioned in another thread. Unfortunately there was no way to bring it out, so it's disconnected under the chip and there is no way to use it.

User avatar
RaTTuS
Posts: 9591
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: FM pin on Pi 3

Tue Mar 01, 2016 10:53 am

it is not routed because of routing problems
it is not brought out and not accessible because it is underneath the chip
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

andybee
Posts: 2
Joined: Sun Apr 27, 2014 8:46 am

Re: FM pin on Pi 3

Tue Mar 01, 2016 11:07 am

Thank you both.

Heater
Posts: 8143
Joined: Tue Jul 17, 2012 3:02 pm

Re: FM pin on Pi 3

Tue Mar 01, 2016 12:24 pm

Is that the antenna pin we e talking about?

Sounds like a challenge to burrow into a board and make contact with it :)

Is it really so that it won't receive anything without that antenna? Not even my home made transmitter nearby? This calls for an experiment.

What software do we need to use the FM radio hardware?

User avatar
RaTTuS
Posts: 9591
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: FM pin on Pi 3

Tue Mar 01, 2016 12:31 pm

you don't want to be drilling into a 6 layer board to find a spot on the other side ;)
your best bet would be to try with the transmitter
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4221
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: FM pin on Pi 3

Tue Mar 01, 2016 1:32 pm

If it was possible to drill a hole through all six layers without breaking an important track, there would already be a hole there. I think they were rather disapointed that they couldn't at least route it out from under the chip.

Heater
Posts: 8143
Joined: Tue Jul 17, 2012 3:02 pm

Re: FM pin on Pi 3

Tue Mar 01, 2016 1:58 pm

I did say it was a challenge. I'll leave it to the neurosurgeons here.

User avatar
ric96
Posts: 1254
Joined: Sun Mar 17, 2013 6:03 am
Location: NOIDA, India
Contact: Website

Re: FM pin on Pi 3

Tue Mar 01, 2016 4:37 pm

Heater wrote:Is that the antenna pin we e talking about?

Sounds like a challenge to burrow into a board and make contact with it :)

Is it really so that it won't receive anything without that antenna? Not even my home made transmitter nearby? This calls for an experiment.

What software do we need to use the FM radio hardware?
If they decided not to connect the antenna, they probably not have connected other circuitry required to control it, until or unless it uses the same connections as that of wifi/BT.
My apologies for shameless YouTube Plugs...
youtube.com/sahajsarup
twitter @sahajsarup
skype srics1996
e-mail: sahajsarup@gmail.com
Blog: http://www.geektillithertz.com/wordpress
Web: http://www.geektillithertz.com

Heater
Posts: 8143
Joined: Tue Jul 17, 2012 3:02 pm

Re: FM pin on Pi 3

Tue Mar 01, 2016 4:54 pm

I have no idea what the FM hardware might be.

I was kind of assuming it only needs a single pin for the antenna and then all the control happens by software control through registers internally and the sound is read by software as well.

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4221
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: FM pin on Pi 3

Tue Mar 01, 2016 5:26 pm

I would assume that the FM receiver stuff is in the GPU area and the details of that will probably not be made public.

The SoC is actually a GPU that has an ARM as a peripheral. The GPU starts the boot, configures all the memory and grants the ARM access to various devices either by mapping their addresses into the ARM address space or by providing API to control them.

gregeric
Posts: 1495
Joined: Mon Nov 28, 2011 10:08 am

Re: FM pin on Pi 3

Tue Mar 01, 2016 6:20 pm

The FM hardware is inside the new BT/WiFi combo chip, BCM43438, nothing to do with the VC4. It can route audio out as analogue stereo, play it out over bluetooth with no CPU intervention once set up, and I think squirt it back PCM to the host CPU. Unfortunately none of which are available on the Pi3 without an antenna.

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4221
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: FM pin on Pi 3

Tue Mar 01, 2016 6:29 pm

Ah. Sorry I was not understanding. Still under the chip and inaccessible though.

Heater
Posts: 8143
Joined: Tue Jul 17, 2012 3:02 pm

Re: FM pin on Pi 3

Tue Mar 01, 2016 7:05 pm

Ah, thanks for the clarification.

Still wondering if it would receive something without an antenna if we shouted at it loud enough. And what software could we use to drive it?

gregeric
Posts: 1495
Joined: Mon Nov 28, 2011 10:08 am

Re: FM pin on Pi 3

Tue Mar 01, 2016 8:01 pm

Before all this kerfuffle over Pi3 & this new fangled SDIO thing, I bought a couple of these http://www.ebay.co.uk/itm/Azuware-BC432 ... SwpDdVGa4B. Looks like a mini PCI-e card, but it's not electrically - the BCM43438's older stablemate the BCM4329 is on board, connecting in much the same way: SDIO for WiFi, Serial, PCM for BT & FM etc I've read up a little (but have been distracted by esp8266 in sdio mode recently) & afaicr the FM is controlled over serial, in common with bluetooth. I was hoping to get it to tune & play audio on its analogue audio outputs just by sending serial commands to it...

User avatar
Hitechcomputergeek
Posts: 28
Joined: Wed Nov 27, 2013 4:29 am

Re: FM pin on Pi 3

Mon Mar 21, 2016 11:47 pm

Screw the BCM43438 - just stick an antenna on a GPIO :P
(edit)
jamesh wrote:DO NOT DO THIS.
(/edit)

FM transmitting has been done before by using a GPIO on the Pi.[Mod link removed] I'll quote from that wiki page:
Below is some code that was hacked together over a few hours at the Code Club pihack. It uses the hardware on the raspberry pi that is actually meant to generate spread-spectrum clock signals on the GPIO pins to output FM Radio energy. This means that all you need to do to turn the Raspberry-Pi into a (ridiculously powerful) FM Transmitter is to plug in a wire as the antenna (as little as 20cm will do) into GPIO pin 4 and run the code posted below. It transmits on 100.0 MHz.
Unfortunately, this is only capable of transmitting FM signals, not receiving them. I was almost inclined to say that with the right software, receiving FM would probably be possible. However, after thinking, I'm not so sure about that anymore - it's quite possible that the hardware is not capable of receiving signals at this speed.
Last edited by Hitechcomputergeek on Thu Mar 24, 2016 4:18 pm, edited 2 times in total.

User avatar
rpdom
Posts: 11860
Joined: Sun May 06, 2012 5:17 am
Location: Essex, UK

Re: FM pin on Pi 3

Tue Mar 22, 2016 6:02 am

Hitechcomputergeek wrote:FM transmitting has been done before by using a GPIO on the Pi.
and is illegal in most countries. Mostly due to the echoes it creates on other frequencies.

This is one reason why the ability to do this was removed on later Pi versions.

Just don't do it.

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4221
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: FM pin on Pi 3

Tue Mar 22, 2016 8:18 am

Hitechcomputergeek wrote:I was almost inclined to say that with the right software, receiving FM would probably be possible. However, after thinking, I'm not so sure about that anymore - it's quite possible that the hardware is not capable of receiving signals at this speed.
People are using the Pi to receive, however they use a faster computer to do the hard work.
https://www.adafruit.com/products/1497
Note that the UK is one place that receiving certain signals is illegal but you're not going to get into trouble unless you tell anyone what you heard, (unlike transmitting when everyone around you knows.) All the very secret stuff is going to be encrypted now anyway, unlike in my youth when we used to listen in to the police frequencies. Fortunately that device can't get down to the fishing boats on around 5MHz where you can learn advanced swearing.

User avatar
Hitechcomputergeek
Posts: 28
Joined: Wed Nov 27, 2013 4:29 am

Re: FM pin on Pi 3

Tue Mar 22, 2016 4:31 pm

rpdom wrote:This is one reason why the ability to do this was removed on later Pi versions.
Do you have a source for this?

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 18214
Joined: Sat Jul 30, 2011 7:41 pm

Re: FM pin on Pi 3

Tue Mar 22, 2016 6:20 pm

Hitechcomputergeek wrote:Screw the BCM43438 - just stick an antenna on a GPIO :P

FM transmitting has been done before by using a GPIO on the Pi. I'll quote from that wiki page:
Below is some code that was hacked together over a few hours at the Code Club pihack. It uses the hardware on the raspberry pi that is actually meant to generate spread-spectrum clock signals on the GPIO pins to output FM Radio energy. This means that all you need to do to turn the Raspberry-Pi into a (ridiculously powerful) FM Transmitter is to plug in a wire as the antenna (as little as 20cm will do) into GPIO pin 4 and run the code posted below. It transmits on 100.0 MHz.
Unfortunately, this is only capable of transmitting FM signals, not receiving them. I was almost inclined to say that with the right software, receiving FM would probably be possible. However, after thinking, I'm not so sure about that anymore - it's quite possible that the hardware is not capable of receiving signals at this speed.


DO NOT DO THIS.

It can get you in to BIG TROUBLE depending on where in the world you live.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

User avatar
RaTTuS
Posts: 9591
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK

Re: FM pin on Pi 3

Wed Mar 23, 2016 8:26 am

http://stakeholders.ofcom.org.uk/enforc ... cement/law
http://www.legislation.gov.uk/ukpga/2006/36/contents
in the UK spamming the FM band will get you in serious trouble

because the GPIO way make for a very messy signal you can expect a visit from some serious people if you happen to be anywhere near
a police station , Hospital , airport

in the US this is probably very similar

so in general don't do it
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

User avatar
Hitechcomputergeek
Posts: 28
Joined: Wed Nov 27, 2013 4:29 am

Re: FM pin on Pi 3

Wed Mar 23, 2016 11:45 pm

:(

Thanks for the warning, though. I didn't realize that the signal was messy enough to be illegal. Kind of a shame, but I guess you could buy one of those cheap low-powered car FM transmitters (like this) - I've seen them as low as $5 here in the US - and hook it to the audio out jack for legal Pi FM transmission.

For an FM receiver, you could also get an FM radio and a USB sound adapter with a mic input (might want to look for one that has a stereo mic input), and hook the headphone jack to the mic input on the sound card.

(But that's so boring...)

Pithagoros
Posts: 559
Joined: Wed Nov 12, 2014 8:16 pm

Re: FM pin on Pi 3

Thu Mar 24, 2016 8:01 am

If you want to play with radio on a Pi, get an inexpensive USB RTL-SDR receiver and install GNU Radio. For RTL2832U based receivers there is kernel support.

No TX but loads of possibilities for projects.

User avatar
rurwin
Forum Moderator
Forum Moderator
Posts: 4221
Joined: Mon Jan 09, 2012 3:16 pm
Contact: Website

Re: FM pin on Pi 3

Thu Mar 24, 2016 9:22 am

I saw a spectrum analyser plot of the Pi transmitting on 30MHz and there were equal-sized outputs every 10MHz up to the limit of the measuring equipment at 120MHz. That includes air-traffic frequencies. They probably continued on up and hit the emergency services above 146MHz.

In the UK, anything that an unlicensed individual builds to transmit is illegal. Unless you are a Radio Amateur and therefore trained to do it properly, all transmitters have to be certified as type-approved; there's a lot of people squeezed into a small space in these sceptered isles. Elsewhere in the world the laws will be different and may be more relaxed.

If you are interested in using your Pi with radio, Google for SDR or Software Defined Radio. Adafruit do a USB receive-only device for about $20 but there are transmitters out there for the Amateur Radio market. You might find it surprisingly easy to get an Amateur Radio license.

User avatar
karrika
Posts: 952
Joined: Mon Oct 19, 2015 6:21 am
Location: Finland

Re: FM pin on Pi 3

Thu Mar 24, 2016 9:48 am

Hitechcomputergeek wrote:I guess you could buy one of those cheap low-powered car FM transmitters
Actually transmitting anything over 1 microwatt (100 µV/m at 30 meters) in the bands reserved for FM radio is illegal. But these car FM transmitters are ok in most countries around Europe since 2006. And they do not require a license.

As a kid I loved tuning in to high power Radio Caroline, Radio London and all the other wonderful pirate radios operating outside UK territorial waters.

I also had a tunnel diode based FM transmitter in my guitar and in summer we were playing and singing on the docks during the regatta spreading joy to (or annoying) all the sailors who tried to tune in to next days weather forecasts. The output was very modest but you could hear us on the radio if you were on the same dock.

Return to “General discussion”

Who is online

Users browsing this forum: beatsal, DougieLawson, Heater, Imperf3kt, Maxwell175 and 54 guests