The simple bat detector uses frequency division to lower the bat’s chirping to a frequency we can hear. For example, if a bat is calling at 91kHz the system will divide it by 16 and put out 5.7kHz. The system is digital, so all amplitude is lost. You’ll just hear clicks like a Geiger counter. Being digital has its advantages though. Unlike similar analog devices that have to be tuned to a small frequency range, the simple bat detector can detect a much wider window.
[Tony] has supplied step by step directions on how to assemble the simple bat detector, along with plans for two different models. He not only encourages people to build there own, but seems to really enjoy seeing their work. He’s posted several images of other people’s builds (pictured above) on his site.
[suneth] has taken this idea in a slightly different direction with his Ultrasonic Batgoggles. Built for a school project in Arts, Media, and Engineering, they actually block your vision so you can try to use echolocation to navigate. You don’t hear the echoes, the processor deciphers that for you. You hear a beep that varies in speed based on the distance you are from an object. On the plus side, you will look totally awesome wandering around trying not to bash your nose on stuff.
[via only hacks]