Bat detectors

[The Dong]

On 04/08/2011 11:43, Chris Strellis wrote:
> I would like to make a nice simple bat detector.  I think our Mr Dong is
> an expert here and I hope he'll chime in. There's loads of info on the
> web but what are the good techniques? I like the simple divide down
> frequency division myself.

I'm not an expert, I can hear bats without biomechanical aids ;)
Here's a link to, many links:

http://bertrik.sikken.nl/bat/index.html

(Many dead links)
The simple bat detector might be a good starting point.

The heterodyne and frequency division remind me of metal detecting 
circuits. The 4024 is used by at least one major metal detector 
manufacturer. If building any of the freq div circuits that use the 
4024, I recommend expanding it a bit with a rotary switch or three way, 
so you can select different freq divisions (look at the 4024 datasheet)
If only for the novelty factor, but I'm sure it would make it even more 
useful for whatever you can think of, if not just bats.

Many of these circuits say to use an ultrasonic electret, which is 
expensive. You might get decent results with a small ordinary one if 
cost is an issue.

Or try a kit?

http://www.alanaecology.com/wildlife/Magenta_Bat_Detector_Kit.html

Though that might be a heterodyne detector.
This detector (heterodyne) is not too expensive (comparatively) and 
looks like all you'll need for any species:

http://www.semafor.co.uk/bat-detector.html#Nottop

Good luck :)