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==Interesting Links== | ==Interesting Links== | ||
[http://sciencelinks.jp/j-east/article/200615/000020061506A0481275.php Development of a Bone-conducted Ultrasonic Hearing Aid for the Profoundly Sensorineural Deaf] | [http://sciencelinks.jp/j-east/article/200615/000020061506A0481275.php Development of a Bone-conducted Ultrasonic Hearing Aid for the Profoundly Sensorineural Deaf] | ||
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[http://home.netcom.com/~t-rex/BatDetector.html Build A Simple Bat Detector] - tons of great info and schematics, see especially the link Bertrik link at the bottom of the page for yet more circuits and groups interested in listening to bats... | [http://home.netcom.com/~t-rex/BatDetector.html Build A Simple Bat Detector] - tons of great info and schematics, see especially the link Bertrik link at the bottom of the page for yet more circuits and groups interested in listening to bats... | ||
==Research Notes== | ==Research Notes== | ||
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I did a whole bunch of reading about "bat detectors". Basically they come in two varieties, the Heterodyne, and the Frequency Division. The former takes e.g. a tunable 8kHz zone in ultrasonic, and moves it into an 8kHz zone in the audible region. You can think of it something like a radio for ultrasonic sounds. It preserves amplitude information, but since it only accesses a tiny fraction of the ultrasonic region at once, you can easily miss lots of stuff. Frequency Division is taking e.g. an 80kHz band of ultrasonic sound, and dividing it down to an 8kHz audible zone. The division is done digitally, so the typical result is a loss of amplitude information; the resulting sounds are comparable to a "Geiger counter" experience of ultrasonic sound. There is also an expensive technique of time expansion - record 1 second of data at e.g. 50kHz, and then play it back at 5kHz for 10 seconds. | I did a whole bunch of reading about "bat detectors". Basically they come in two varieties, the Heterodyne, and the Frequency Division. The former takes e.g. a tunable 8kHz zone in ultrasonic, and moves it into an 8kHz zone in the audible region. You can think of it something like a radio for ultrasonic sounds. It preserves amplitude information, but since it only accesses a tiny fraction of the ultrasonic region at once, you can easily miss lots of stuff. Frequency Division is taking e.g. an 80kHz band of ultrasonic sound, and dividing it down to an 8kHz audible zone. The division is done digitally, so the typical result is a loss of amplitude information; the resulting sounds are comparable to a "Geiger counter" experience of ultrasonic sound. There is also an expensive technique of time expansion - record 1 second of data at e.g. 50kHz, and then play it back at 5kHz for 10 seconds. | ||
The Bertrik page lists many sources for bat detector kits, but all but one appear to be dead, and that's not so much a kit as an offer of a custom PCB and BOM, see [http://home.earthlink.net/~bat-detector/TheBatShop.html Tony Messina Bat Shop]. You must order the entire BOM yourself. The list of products fairs much better, with most still being available, but the prices are quite high. Market entry is | The Bertrik page lists many sources for bat detector kits, but all but one appear to be dead, and that's not so much a kit as an offer of a custom PCB and BOM, see [http://home.earthlink.net/~bat-detector/TheBatShop.html Tony Messina Bat Shop]. You must order the entire BOM yourself. The list of products fairs much better, with most still being available, but the prices are quite high. Market entry is about $80, and the sky is the limit - there are some thousand dollar+ products for "professionals". | ||
Bertrik himself in 2006 was working towards an [http://bertrik.sikken.nl/bat/advdiv.htm amplitude preserving] version of the Frequency Division idea, but he appears not to have finished the effort. This is a promising approach to a more convenient device for listening to all ultrasonic sound. He also has some better info up at [http://wiki.sikken.nl/index.php?title=DigitalBatDetector Digital Bat Detector Wiki] | Bertrik himself in 2006 was working towards an [http://bertrik.sikken.nl/bat/advdiv.htm amplitude preserving] version of the Frequency Division idea, but he appears not to have finished the effort. This is a promising approach to a more convenient device for listening to all ultrasonic sound. He also has some better info up at [http://wiki.sikken.nl/index.php?title=DigitalBatDetector Digital Bat Detector Wiki] | ||
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That's the name of the ultrasonic toy that I ordered from Amazon. I received it on Wednesday, it works once you get a working 9V battery into it. It appears to be an untunable hererodyne circuit, but there is no information on what frequency it operates at. I was able to hear their "bat sound" emitter (which is actually just a nice wave pattern), plus the sound of CFL bulbs and the sound of bouncing coins. Everything else (computers, the North Paw, etc) was quiet. | That's the name of the ultrasonic toy that I ordered from Amazon. I received it on Wednesday, it works once you get a working 9V battery into it. It appears to be an untunable hererodyne circuit, but there is no information on what frequency it operates at. I was able to hear their "bat sound" emitter (which is actually just a nice wave pattern), plus the sound of CFL bulbs and the sound of bouncing coins. Everything else (computers, the North Paw, etc) was quiet. | ||