It has two.
Bat detector circuit diagram.
From popular electronics 1994 the circuit shown here is for a heterodyne 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.
For the bat detector circuit i didn t design a pcb but soldered the prototype on perfboard.
I 3d printed an enclosure for the circuit and two knobs for the volume and frequency control.
Click image for a larger jpeg view.
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.
At the time although all stages worked correctly it was not possible to combine them to produce a working design.
The signal from the microphone is filtered to remove interference and amplified then frequency divided using a counter.
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.
Schematic of a heterodyne bat detector.
The circuit has three stages.
How does the bat detector work.
Detection of the high frequency clicks bats emit must be done with an ultrasonic transducer for two reasons.
Block diagram the block diagram shows the circuit sections for a simple frequency division bat detector.
Schematic and construction the original design concept for this equipment was developed by john errington msc and sylvain frenehard at northumbria university.
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.
Construction is straight forward and can be laid out very much as the schematic shows.
If you want to design your own you can grab the kicad schematic here and design your own pcb version.
The circuit diagram in figure 2 shows the complete project and it really is as simple as it looks.
The preamp is based on a standard dual opamp and although various types will work i found the tl072 to be the liveliest.
A schmitt trigger circuit prevents false counts.
Recording and analysing bat call audio is a great way to achieve this monitoring especially if it can be fully automated.
