Ultrasonic. - Here is Circuit Schematic Simple Bat Detector using LM386 and CD4024. The Simple Bat Detector is a frequency division type device. Frequency division type detectors allow you to hear ultrasonic sound by digitally scaling the frequency down into the human hearing range. For instance, a western pipistrelle bat emits ultrasonic sound in the range of 53 to 91 kHz. If you divide that frequency by 16, the new frequency range is 3.3 to 5.7 kHz, easily within our hearing range. Because the division is done digitally, all amplitude information is lost. Ultrasonic sources processed by the detector convert to sounds like geiger-counter clicks and chirps.
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| Figure 1. Simple Bat Detector using LM386 and CD4024 (Source: www.pw1.netcom.com) |
The basic circuit of the Simple Bat Detector is shown in the schematic diagram to the right. It is essentially composed of 3 integrated circuits, or ICs. The signal from an ultrasonic transducer is fed to IC-1, an LM386 audio amplifier, which is configured to provide a signal gain of 200. The signal is coupled to IC-2, a second LM386, by a .05 uf capacitor. IC-2 is configured to provide an additional gain of 20, for a total system gain of 4,000. The output of IC-2 is direct coupled to the input of IC-3, a 7 stage CMOS digital divider circuit. The input stage of the divider acts as a zero crossing detector, triggering on the negative transition of the signal from IC-2. The divide by 16 output is connected to a potentiometer, which serves as an audio level control. A high impedance ceramic earphone is connected to the output of the level control. The 10K level control is a small printed circuit pot that is set and forgotten. The detector circuit is powered by a nine volt battery. ( The numbers next to the IC nodes refer to the pin numbers of the IC's. Note the additional pins listed at the bottom of the schematic that need to be tied to ground. )
A major advantage of a frequency division detector is that it is a wide band device ... that means it will let you hear all detectable bat sounds without the need to tune the detector to any particular frequency. Heterodyne detectors, which process ultrasonic sound in the analog domain, only convert a small range of frequencies at any given time - you must select which frequencies to listen to. If you tune up around 60 kHz to listen for a pipistrelle, you may not hear the big brown bats flying nearby. The frequency division detector works in the digital domain, converting the full spectrum of sound that the transducer is able to detect. So you get to listen to all of the ultrasonic sounds around you, without missing anything due to unfortunate tuning choices. I feel this no-knobs-needed characteristic of the frequency division detector makes it a great choice for the casual bat observer, and student.
The Original Article : "Build a Simple Bat Detector"
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