Summer is almost upon us and with it comes the biting insects that we all love. While we may not like all the gnat’s, mosquitoes, fly’s, etc., biting us but there are plenty of other animals that look forward to this time since for them it is a feast, this includes
Birds - from swallows to hummingbirds
Amphibians and reptiles - like frogs and toads
Arachnids - including garden spiders and my favorite - jumping spiders
And, most importantly for this post, Bat’s
Bat’s, like most animals, communicate through vocalizations. The difference with bats is that many of the vocalizations they make are beyond the range that we can hear (many of their calls are in the ultrasonic range).
In this project I’ll be using different techniques to convert ultrasonic bat calls from ultrasonic frequencies down to frequencies that we can hear. Human hearing range extends from 20Hz up to 20kHz (if you are young), but bat vocalizations extend from 12kHz up to 160kHz.
The main goals of this project are to:
listen to bats
identify bat species
There are 2 main methods used to convert ultrasonic bat calls to frequencies within our range of hearing.
The First approach uses the heterodyne method. This involves combining an internal reference frequency with a detected sound. The output that you her is the difference between the two frequencies. A simple example concerns a 42kHz bat call. The heterodyne technique would compare the call to a 40kHz reference frequency and the audible output would be a 2 kHz tone
The Second approach divides the detected frequency. Using this technique the frequency is usually divided by 16 – so a 42kHz bat call would come out as a 2.6kHz tone.
Each method has it’s pro’s and con’s. Before we can look at them I’ll first have to get the circuits working. Which I hope to show in the next post.