[Community] GTA04A5 ready to be pre-ordered

[Dr. H. Nikolaus Schaller]

Am 07.11.2013 um 00:02 schrieb NeilBrown:

> On Wed, 23 Jan 2013 12:20:01 +0100 "Dr. H. Nikolaus Schaller"
> <hns at goldelico.com> wrote:
> 
> Seeing you are considering trying again for the GTA04a5, I thought I might
> re-visit these issues:
> 
> 
>> 
>> Am 22.01.2013 um 12:29 schrieb NeilBrown:
>> 
>>> On Tue, 22 Jan 2013 10:02:38 +0100 "Dr. H. Nikolaus Schaller"
>>> <hns at goldelico.com> wrote:
>>> 
>>> 
>>>> Preliminary (there may still come minor changes coming from PCB
>>>> Layout tuning and from first production feedback) schematics can be found here:
>>>> 
>>>> 	<http://projects.goldelico.com/p/gta04-main/downloads/48/>
>>> 
>>> Thanks!
>>> 
>>> One thing that has always bothered me a little bit is that the FM transceiver
>>> is wired for digital IO rather than analog.  That means that the CPU needs to
>>> be active to copy sound around in order to listen to the radio.  If the
>>> LOUT/ROUT pins were connected to the line-in pins on the audio chip you
>>> should be able to listen to the radio with the CPU off.
>> 
>> Yes, that should be possible.
>> 
>>> It would mean that you couldn't get the same fidelity if you wanted a digital
>>> copy of the broadcast, but I wonder if that really matters.
>>> 
>>> What is the expected use-case of the FM radio?  If it is just for listening
>>> to, the current config doesn't seem to be optimal.
>> 
>> Well, the TX direction is more interesting since it can play sound (incl. navigation
>> information) to a car radio. By using text2speech. And mix with sound.
>> 
>> Connecting to the Audio in is a problem since we have already connected them
>> to the headset jack. So that it is possible to record sound fed into the headset
>> jack. I.e. portable audio recorder...
> 
> Is the "portable audio recorder" use case more valuable than the "FM radio
> without excessive power usage" use case?  I would be happy to sacrifice the
> stereo-aux-in if it meant I could listen to the radio for longer.
> 
> For the price of another analogue switch like the one you use to isolate the
> headset outputs (U703) you could support both FM and AUX inputs.  Maybe that
> price is too high??

I will check. It is probably less a cost issue (such chips are around 50ct) but space
and (shielded) wiring. But since headset jack and the Si4721 are not far away
from each other it could work.

> 
>> 
>> And the FM-analog out are multiplexed with the digital interface on the Si4721.
>> So we would need some analog/digital switching circuits where we don't have
>> space for :(
> 
> I wouldn't suggest enabling both the analogue and digital interfaces.  Just
> the analogue.  Digital might be nice but isn't really necessary.

Well, it gives a better S/N since the signals are already A/D converted in the Si4721
and just need to be arecord >file if you want to capture signals.

> 
> 
>> 
>>> Related: have you thought about connecting the bluetooth PCM interface
>>> directly to the TPS chip in the same way that the Modem's PCM interface is
>>> connected?
>>> 
>>> That should allow the use of a bluetooth headset on a phone call without any
>>> CPU intervention.
>> 
>> Yes, that could work to add these 2 wires (at least in the schematics - I don't
>> know if we can squeeze them into the PCB wire hairball). And I have checked
>> that these two pins at the TPS65950 come up in GPIO (input) mode, i.e.
>> don't interfere.
>> 
>> One issue could be that there is no BSP clock for that interface on the TPS side.
>> I.e. it is shared with some other interface and I am not sure how to operate it correctly.
>> So we might have to wire up something else to really make it work.
> 
> The clock for the bluetooth interface and the voice interface are shared.
> So the clock from the GSM module drives the whole chain from bluetooth
> through TWL4030 to GSM.

Well, we likely can't use the BT PCM to play music from memory? I put it on the checklist as well.

> 
>> 
>>> Just thinking out loud - looking forward to the A5 being a reality!
>> 
>> So I find both proposals really good, but I hesitate to add them... may need a lot
>> of work to add, and may finally not work. The problem with hardware is that
>> we have to do it 100% right or risk scrapping a big set of PCBs or costly rework
>> in the production line. Unfortunately there is no apt-get upgrade or git pull for
>> the wires on a PCB...
> 
> :-)  I'm waiting for the day when a 3D printer can print a fully populated
> multi-layer PCB (under voice command of course).

Me too. Incl. printing the wires and transistors on a Si chip :)

> 
> Maybe in the spirit of openness a vote might be  instructive.
>  Does anyone actually want stereo aux input through the 2.5mm jack?
>  Does anyone actually want to listen to the FM radio without wasting power?
> 
> (no and yes for me).
> 
> Thanks,
> NeilBrown