Optical DIY mic idea

  • Thread starter Thread starter dres
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Warning - Time Warp
Thought I'd open this thread up to see if anyone has any intervening ideas or progress. Most of the posters haven't been around for awhile.

Here's a link to one company's simplified design for use in an MRI environment where electircal signals would be adversely affected by the magnetic fields.
http://www.phone-or.com/temp/data/MRI_wp.pdf

Here's another from a DIY'er - he uses a PIN (positive intrinsic negative) diode, but I can't seem to find any rated at sonic frerquencies - just microwave and beyond, due to its mechanism of action.
http://www.williamson-labs.com/laser-mic.htm

Here's a primer on PIN diodes:
http://www.microsemi.com/micnotes/701.pdf

I am thinking of modifying the laser/reader on a CD player, but still need some kind of analog detector for a variable intensity light source at sonic frequencies.

Any ideas?
 
<Thought I'd open this thread up to see if anyone has any intervening ideas or progress. >

Crazydoc,

Gottcha--you knew I will see it :D :D :D
Thanks for bringing it to attention--very nice thread!
There are two ways of building optical mic--analog and digital, with fiber optic pipe as a transmission line. I remember reading Stephen Paul's post on RO, where he was talking about his ideas about digital one. If I remember correctly, he was thinking of doing this. I tryed to make a search there, but the thread might be erased. If I am not mistaken, I vaguely remember D. Josephson also talking something about it on RAP.
All of these designs, including Sennheiser and Phone, rely on reflection of the beam from the membrane.
My thought is making "analog" ribbon one, so the ribbon is placed in between of the optopair. Here, think of the cost--20 bucks at the most for the parts. The major challenge would be linearity and noise performance, although it is very doable IMO.
Currently I am looking for the best photodiode available for this application. If you have any ideas please let me know.

Have a look at:

http://www.centrovision.com/tech2.htm

and

http://www.udt.com/pdf/pd_char.pdf

BTW, Crazydoc, I moved from Tempe AZ to SLC just a couple months ago. It's coooold here...
 
Marik said:
<Thought I'd open this thread up to see if anyone has any intervening ideas or progress. >

Crazydoc,

Gottcha--you knew I will see it :D :D :D
Thanks for bringing it to attention--very nice thread!
There are two ways of building optical mic--analog and digital, with fiber optic pipe as a transmission line. I remember reading Stephen Paul's post on RO, where he was talking about his ideas about digital one. If I remember correctly, he was thinking of doing this. I tryed to make a search there, but the thread might be erased. If I am not mistaken, I vaguely remember D. Josephson also talking something about it on RAP.
All of these designs, including Sennheiser and Phone, rely on reflection of the beam from the membrane.
My thought is making "analog" ribbon one, so the ribbon is placed in between of the optopair. Here, think of the cost--20 bucks at the most for the parts. The major challenge would be linearity and noise performance, although it is very doable IMO.
Currently I am looking for the best photodiode available for this application. If you have any ideas please let me know.

Have a look at:

http://www.centrovision.com/tech2.htm

and

http://www.udt.com/pdf/pd_char.pdf

BTW, Crazydoc, I moved from Tempe AZ to SLC just a couple months ago. It's coooold here...
Click to expand...

Yes, I knew you'd see it. This thread is more applicable for what we're discussing.
You are far beyond me in knowledge and experience with mic construction, but I might luck into a good idea once and awhile.

Thanks for the links on photodiodes. I'll read them when I get a chance.

I grew up in Denver, so I can remember what the weather was like up your way. Last time I visited in the winter about 10 years ago it snowed about 29 inches in 24 hours.
I played at the PF Chang Arizona marathon here yesterday - about 50 degrees when we set up at 6:00 AM, and 70 when we finished at 10. Had a garage sale in the afternoon - about 75 degrees. But hey, we pay for it May through September.
 
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