Listen-in to the world of bats with this low-cost b.f.o. detector

The author’s original purpose was to design a simple Bat-Band Convertor that would “really work”. The resulting Bat-Band Convertor project uses just a single IC and a handful of components to deliver surprisingly good performance.

The circuit has been named a Bat-Band Convertor, since it not only detects bats, but converts their sounds to frequencies that fall within the range of human hearing. In so doing, it gives a reasonably faithful representation of a bat’s sound.

It is well known that bats use ultrasound for navigation and the location of prey. A bat will emit rapid bursts of ultrasound – typically 10 to 200 times a second, increasing in rapidity as a bat closes on its prey. These bursts are in the region of 12kHz to 150kHz, with wide variations in frequency, depending on the species. They are high amplitude sounds, and the first time the author used a bat detector, he was surprised at the volume that a bat emits. A typical bat will “scream its little lungs out”!

The Bat-Band Convertor is a highly sensitive circuit that “hears” over the range of 13•6kHz to 180kHz. The only limiting factor will be the transducer that you use. The author settled on a standard 40kHz ultrasonic receiver transducer, and this gave good performance up to about 50kHz, with sensitivity dropping off around 60kHz. However, it was able to “hear” well above 100kHz.