MCSI breakthrough

[Das Signal]

Hi Rafael, Mychaela,

I just tested an analog phone call on the FCDEV3B and I'm glad to report
it worked very well! The test setup is as follows:
- a standard 8ohm speaker which I soldered to 2.54mm female cables and
connected to the appropriate header on the board
- an electret microphone also soldered to 2.54mm cables and connected with
the correct polarity to the FCDEV3B

I recompiled the fc-magnetite firmware, flashed it and followed Mychaela's
instructions in https://www.freecalypso.org/members/falcon/fcdev3b/fcdev3b-userman-1.25.pdf
Then I tested voice calls with ATD<phone number>; and it worked perfectely,
audio was crystal clear on both ends. So this configuration is indeed shown
to be working fine! Although Rafael be careful when connecting a sound card,
you don't want to overload the microphone input which could cause in the worst
case permanent damage to the amplifier if the input level is too high.

--DS

On Sun, Mar 31, 2019 at 08:53:52PM -0300, Rafael Diniz wrote:
> Hi Mychaela,
> 
> Thanks for the support. I prefer first to have the speaker and Mic
> you'll provide us working fine here. As a later experimentation, I'd
> like to try to match the impedance of the sound card with the fcdev3b
> audio I/O and may be add a switch to change between official mic/speaker
> and AUX audio I/O. Just ideas for now.
> 
> Cheers,
> Rafael Diniz
> 
> 
> On 3/31/19 7:54 PM, Mychaela Falconia wrote:
> >> Hi Mychaela and Das Signal,
> >> Is there a way I could install two audio connectors for MIC and Speaker?
> >> For the use I have in the lab with the FCDEV3B it would be more interesting.
> > 
> > I am afraid that I don't really understand the question.  Are you
> > asking for a way to convert the speaker and mic hook-ups on the FCDEV3B
> > to audio connectors like the ones on a laptop, such that you could then
> > plug off-the-shelf end-user audio stuff into them?
> > 
> > If that is your question, then I don't have an answer to it, as I am
> > quite illiterate in the realm of audio myself - just producing the
> > circuits which are currently on the board was an extremely difficult
> > struggle for me during the design phase.  Someone who understands
> > analog audio much better than I do would need to review the circuits
> > which are currently on the board and figure out what can be done with
> > them, other than what I found to work.
> > 
> > As I already said before, I would be more than happy to send one of my
> > voice kits (speaker and mic outfitted with wires and connectors that
> > connect to the FCDEV3B) to each of you (both Rafael and DS), but if
> > you desire something different, you will have to figure it out
> > yourselves.  You will need to start with the Leonardo schematics:
> > 
> > ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_rev05.pdf
> > 
> > TI's Leonardo speaker and mic circuits are depicted on page 3 of the
> > above PDF; the corresponding circuits on the FCDEV3B are almost
> > identical, with only a few differences:
> > 
> > * Where the original Leonardo schematic drawing shows physical speaker
> > and mic parts, on our FCDEV3B we have a two-post header in the place
> > of each, for the physical speaker or mic to reside off-board;
> > 
> > * The differential input to the TPA6203A1 loudspeaker amplifier comes
> > only from EARN&EARP on the FCDEV3B (not from AUXON&AUXOP), and the
> > gain control resistor values are different, tuned to produce 3.6 V of
> > swing on each leg of TPA6203A1 output in our configuration when the
> > output from the Iota ABB (input to the TPA6203A1) is at the maximum;
> > 
> > * C333 and C334 footprints are omitted;
> > 
> > * HSP3xx ESD protection features are also omitted.
> > 
> > The above is all I know; from here onward you have to use your own
> > audio knowledge, which I lack.
> > 
> > Sorry for being of so little help,
> > Mychaela aka The Mother
> > _______________________________________________
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> > Community at freecalypso.org
> > https://www.freecalypso.org/mailman/listinfo/community
> > 
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