> Funny you should ask.  Ran into this this weekend...
>    http://www.mitedu.freeserve.co.uk/Circuits/Misc/Sp-mic.htm

That looks like a pretty crappy circuit.  All the gain is in a single
stage and depends on the I/V characteristics of the first transistor's B-E
junction.  Yuk.  This could be cleaned up with some feedback.

I'm also not convinced that loading the speaker to its characteristic
impedence is the best way to use it as a microphone.  Maybe it's true, but
it's not immediately obvious to me.  I can see some reasons for doing it
either way.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics