If you are a reader of Make Magazine you may remember seeing a "Bat Detector" as a weekend project. That was back in 2006. In the summer of 2010 I ordered some circuit boards from Tony Messina who designed this circuit. And last night, in the summer of 2011, I finally put together 3 of these neat little ultrasonic frequency division bat detectors. It took a while, but it was totally worth it.
I wasn't able to record any bats as they were scarce last night, but here are a couple of sounds that have an ultrasonic component to them. Rubbing fingers together and water running from a faucet. The water faucet sound clip sounds very much like my Geiger counter in the presence of radiation.
I don't have much to say about the construction of the bat detectors. I really just wanted to post about them to help spread the word. I think it is great when makers like Tony share their circuits for all to enjoy and I also appreciated buying the circuit board from him as I wanted to make several bat detectors for friends. Below is a picture of an enclosure being modified to accept a bat detector circuit.
As for enclosures I just looked through my junk boxes until I found something that would work. In the picture below you can see I used a slot car throttle for one of them. It almost closes all the way but the 9v battery I put in the handle is just a touch too big.
The other enclosures I used are a cell phone holster with the plastic box from a laser pointer inside it and just a plain old black otter box. I think the otter box will be useful when camping because it is waterproof until you open it up to use it and the slotcar throttle is neat because it kind of looks like a ray gun from science fiction. Future upgrades include bat like graphics to be applied.
I am really pleased I finally put the time into making these. It took about an evening for all three including enclosures. Right after finishing the first one I took it outside and within 5 minutes I heard a clicking sound. I looked to the dusky sky and there was a bat fluttering about before flying off over the roof. I didn't see or hear anymore bats that night, but that one literally put a smile on my face. Too fun!
Final thought; Go do this, but don't drag it out for 5 years like I did.