MCSI breakthrough

Rafael Diniz rafael at
Sun Mar 31 23:53:52 UTC 2019

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.

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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