MCSI breakthrough

Das Signal das.signal at
Sun Apr 7 19:02:27 UTC 2019

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
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.


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:
> > 
> >
> > 
> > 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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> > 
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