Circuit Diagram Wiring

Posted on Feb 7, 2014

This Bat Detector Circuit is authored by Chris Eve. Basic tests with a variety of salvaged electret microphones all showed good response to 50kHz and beyond, the smaller the unit the better the response. My tests indicate that a small electret microphone has at least some response to 100kHz and that this response is reasonably flat  to at least

Circuit Diagram Wiring
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50kHz. The microphone I use is approximately 6mm in diameter and can be mounted within the body of a 3. 5mm jack plug. Having the microphone socketed rather than fixed within the detector case is optional, but gives further opportunity to experiment with uni-directional or Pressure Zone  modules (see below), or other microphones mounted remotely from the electronics. This bat detector 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. 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...

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