If you want to design your own you can grab the kicad schematic here and design your own pcb version.
Bat detector circuit diagram.
I 3d printed an enclosure for the circuit and two knobs for the volume and frequency control.
A schmitt trigger circuit prevents false counts.
Click image for a larger jpeg view.
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.
Schematic of a heterodyne bat detector.
This was first presented by popular electronics magazine as an ultrasound detector in 1994.
A preamplifier to boost the signal from the microphone a divider to down convert the frequency of the bat to something we can hear and a power amplifier to drive the loudspeaker.
From popular electronics 1994 the circuit shown here is for a heterodyne bat detector.
Schematic and construction the original design concept for this equipment was developed by john errington msc and sylvain frenehard at northumbria university.
Build an enhanced simple bat detector view experiment home built frequency division bat detector view experiment chris eve s bat detector circuit view experiment bat detector circuit with leds to give a visual indication of a bat s presence instead of reproducing the audio at a lower frequency.
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.
The circuit has three stages.
For the bat detector circuit i didn t design a pcb but soldered the prototype on perfboard.
It has two.
Construction is straight forward and can be laid out very much as the schematic shows.
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.
The signal from the microphone is filtered to remove interference and amplified then frequency divided using a counter.
How does the bat detector work.
Detection of the high frequency clicks bats emit must be done with an ultrasonic transducer for two reasons.
Recording and analysing bat call audio is a great way to achieve this monitoring especially if it can be fully automated.
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.
Block diagram the block diagram shows the circuit sections for a simple frequency division bat detector.