The signal from the microphone is filtered to remove interference and amplified then frequency divided using a counter.
Bat detector circuit diagram.
From popular electronics 1994 the circuit shown here is for a heterodyne bat detector.
Firstly such transducers are very responsive to ultrasound and thus produce large output voltages upon detection as compared to a generic audio microphone.
The circuit diagram in figure 2 shows the complete project and it really is as simple as it looks.
At the time although all stages worked correctly it was not possible to combine them to produce a working design.
I 3d printed an enclosure for the circuit and two knobs for the volume and frequency control.
The preamp is based on a standard dual opamp and although various types will work i found the tl072 to be the liveliest.
Block diagram the block diagram shows the circuit sections for a simple frequency division bat detector.
The by far most popular method for bat detectors appears to be the heterodyne down converting if you judge by the number of commercial and home built circuits frequency compression or time lapse this is the most advanced technology based on digital signal processing of the sampled bat sounds but it also requires the most advanced electronics.
Each of the four amplifiers in the quad op amp ic is used as a building block and these correspond quite closely with the functions shown in the block diagram.
Recording and analysing bat call audio is a great way to achieve this monitoring especially if it can be fully automated.
Click image for a larger jpeg view.
If you want to design your own you can grab the kicad schematic here and design your own pcb version.
How does the bat detector work.
This particular bat detector device can be run off 12 volt batteries and be deployed in the wild for days weeks at a time with data being transmitted every now and again via a lora radio link.
Resistors r3 and r4 were selected for high gain in ic1 a.
Schematic of a heterodyne bat detector.
Detection of the high frequency clicks bats emit must be done with an ultrasonic transducer for two reasons.
The circuit has three stages.
For the bat detector circuit i didn t design a pcb but soldered the prototype on perfboard.
This was first presented by popular electronics magazine as an ultrasound detector in 1994.
A schmitt trigger circuit prevents false counts.
It has two.
Construction is straight forward and can be laid out very much as the schematic shows.