Bat detector

[hystrix]

Hi Keviom,

The electret microphone I use is totally passive. It plugs into the Headphone out/Mic in socket on the Wolfson card. I posted some wiring information on my website which may be useful.

One word of advice when using the same type of microphone that I have used - don't knock the actual microphone during recording; it's really sensitive. If you do, you'll get clipping and miss parts of the recording. I'm working on an improved design.

[sandyroman]

I too have been interested in bat call detection. Bertrik's pages and info are very good. 10 years ago or so, when I got interested in this, Knowles had invented the Sisonic mircophone. It was a freefloating silicon microphone. Very small, like a matchhead. Invented specifically for the cell phone market.

They had some that were broadband i.e. *flat* response to from ~1khz - 100Khz, with some wiggles going to 200KHz. Awesome unit. cost about $6.50 at Digikey. I ordered some and made a mouse microphone for a researcher. These would be awesome for such a project. Some were straight mics and some had integrated amplifier/buffers.

Unfortunately, looking over Digikey, I only see units rated for 20 Khz. They might have extended response. I had emailed and called Knowles about the mics I was interested in. They sent me a proprietary set of data I believe - showing the wiggles.

I don't know if the mics I ordered still exist or even what number they were. Maybe there was no market and they were taken out of production? I couldn't say. They were a fantastic product, and could possibly replace specialty mics that were $100 but needed a $1K - $3K preamp!

All bells and whistles would be a high sampling rate unit 100-200 KSamp/sec rate followed by a mathematical transform that down shifts the carrier frequency to the human audio band, (and does time expansion) while preserving the harmonic content. One Flemish EE Prof. described such a project, but he got married and changed his name!

I don't quite have time this week, but will definitely look around to see what happened to the Sisonic unit.

Bat detector folks are unfortunately a niche market!

[sandyroman]

Update. I looked at Digikey and found http://www.knowles.com/download/file?p=SPU0410LR5H.pdf is the only one they have currently (Feb 2015) that displays a frequency response above 10Khz. This unit goes from 100 Hz to 80 Khz with a 10 dB peak at 25Khz and an -8 dB broad dip at 60 KHz. That is not flat, nor 200 Khz, but it is still a lot of microphone for $1.84

Digikey data sheets http://www.digikey.com/catalog/en/partg ... series/102
SPU0410LR5H-QB http://www.digikey.com/product-detail/e ... ND/2420983

So there is still hope for a broad band mic.

[davidmam]

I've been using the dodotronic mic with the Pi. It works fine but there is a catch.

Arecord will not recognise the microphone as the recording frequency (250kHz) is too high. You need to change the code and recompile aplay in order to get ti to work. Yes, it contains a hard coded literal maximum for the frequency it will recognise.

When that is done, it works fine with the dodotronic ultramic 250k.

I'd like to find a USB linked ADC chip that I can put a cheaper mic onto - the MEMS microphones are reputedly the best ones to go for.
..d