Bat detector

The echolocation of bats has grown to a field of science since its detection and much is still being discovered. For the beginner, a bat detector is a way to better find bats, like some smaller species hunting very low or species emerging very late in almost complete darkness. As experience grows one learns to distinguish the sound patterns and associate them with certain species - but this subject fills entire books on its own and we will therefore restrict ourselves to the underlying electronics.

There are three different styles of detection:

Heterodyning detectors - a frequency can be adjusted and is combined with an internal oszillator, thus producing an audible result

Divider - a wide range of frequencies is scanned by dividing all frequencies to audible sound

Slower replay - Ultrasonics are recorded digitally and replayed more slowly

Detectors may be built relatively easily for the first two systems. Dividers have the advantage that bats will be detected over a wide range of frequencies even if their call frequency is not known. The result, however, is a coarse clicking sound and distinguishing species is impossible. Heterodyning detectors monitor only a small chosen range of frequencies but retain the feel of the call, enabling the observer to distinguish species by frequency and sound characteristics with some accuracy (at least where we live, with only 5 species frequent of around a dozend which may occur in the vicinity). In addition to the call, the flight patterns, size, surrounding habitat, and behaviour of the bat should be taken into account when trying to put a name to the species.

After a period of experimentation with different schematics I developed two boards from these:

	TCA440-mixing receiver minimum number of components can be build by "beginners" ideal for workshops speaker (headphone optional) optional time marker
	To be able to build the receiver in workshops I have had some circuit boards made by a commercial manufacturer who does high quality and already drills the necessary holes. Although such a kit is a nice "one weekend project" I am going to abandon this board because the following NE612 design provides more sensitivity and more options at only a slight increase in costs.
	NE612 mixing receiver good sensitivity (20..60 kHz) more linear and less noise optional time marker and frequency counters

The NE612-receiver is not a project for beginners, but for tests I built up some modules (like the circuit board shown above), which only need the external components and of course a case. Therefore they actually can be finished by a "beginner". Just email me to find out, if there are boards or ready-made components left.

I also recommend Tony Messinas Homepage. Tony presents a kit for a very simple but effective dividing detector.

Workshop in Kiel

New: I always wanted to add a low-cost frequency display, but also I wanted to reduce the number of wires running to the different controls. So I did a redesign - see here for details.

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