Ultrasonic / Bat detector


Posted on Mar 18, 2013

I have found this circuit to have better sensitivity, both in distance to a visible bat and in audio frequency, than some other published circuits using a 40kHz transducer with 4000x gain amplification, though the 40kHz transducer I used for the comparison may have a bearing on these results. The high-pass filter is included purely to help eliminate the circuit being triggered by ambient noise. The filter is a 4-pole Chebychev with a very steep roll-off below 15kHz. There is virtually zero response at 10kHz and below. This type of circuit relies on the wanted signal being loud enough to trigger the CMOS counter, so the less unwanted signal that reaches the circuit the better.


Ultrasonic / Bat detector
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Ultrasonic / Bat detector - image 1
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Whilst any of the basic circuits based around a 40kHz transducer will perform adequately for the detection of bats calling within that frequency range, which includes many of the more common species, this circuit will give much better indication of the presence of less-common bats that call at lower frequencies, around 20kHz, as well, hopefully, those at somewhat higher frequencies. When used at dusk, when individual bats are still visible, pointing a unidirectional microphone at a solitary bat indicates a usable range of at least 100ft (30m). Bats actually call very loudly indeed ... it's probably a good job we cannot hear them, else they would keep us awake! My circuit was built in a metal box, because that was what I had to hand, using point-to-point wiring on a ground-plane. Perforated strip-board should be perfectly adequate and probably a lot easier to fault-find should you make a mistake. I do not have nor intend to produce a pcb layout, so please do not ask for one, though if you should feel the need to produce one and have the inclination to share it I would be only too willing to include it (or a link to it) on this page. The circuit may be more susceptable to interference from electronic sources if built in a plastic container. Current consumption is around 15mA with no audio output, so a PP3 battery should last for several evenings unless you have got a lot of bats in your area. For regular or extended use,...




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