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Date: Sun, 23 Aug 2015 18:27:07 GMT
From: falcon AT ivan DOT Harhan DOT ORG (Spacefalcon the Outlaw)
Message-Id: <1508231827.AA21909@ivan.Harhan.ORG>
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Microphone footprint woes
Reply-To: geda-user AT delorie DOT com

Richard Rasker (rasker AT linetec DOT nl) wrote:

> Correct me if I'm wrong, but I don't think that this is an SMD part, and
> that you're supposed to simply solder wires to the contacts.
>
> For SMD type microphones, search for "MEMS Microphone", e.g.
> SPW2430HR5H-B from Knowles.

Thank you for shining the light on my ignorance!  As I have just
learned, the type of microphones I've been looking at are called
electret condenser: they are the type that's been used in the
old-fashioned cellphones of the early 2000s, they are what the GSM
chipset I'm using has been designed to work with, and I don't feel
like changing to MEMS - my motto in this project is Do Not Innovate.

And I also just learned why ECMs are generally not made in SMT form
factor: they can't withstand the heat of reflow soldering.  This part
certainly explains why most cellphones I've examined have their
microphone on wires or on a little strip of flex whose other end is
hotbar-soldered to the main PCBA, and very few of these old phones
have their microphone directly on the main PCBA.  As for the few
phones that did the latter (Openmoko GTA02 and Pirelli DP-L10 do that,
which is where I got my naive idea of doing the same), it looks like
there were some very few electret condenser microphones made in SMT
form, but they are now "obsolete" and unobtainium.

My solution: I'll put a two-pin header on my board instead of the
microphone part, and make the actual microphone a post-board addition.
The same as I already did with the loudspeaker.

Thanks again for the education,
SF