Bats use echolocation to see objects in front of them. They emit an ultrasonic pulse around 20 kHz (and up to 100 kHz) and then sense the pulses as they reflect off an object and back to the bat. It’s the same type of mechanism used by ultrasonic proximity sensors for object-avoidance. Humans (except perhaps the very young ones) can’t hear the ultrasonic pulses since the frequency is too high, but an inexpensive microphone in a simple bat detector could. As it turns out bat detectors are available off the shelf, but where’s the fun in that? So, like any good hacker, [WilkoL] decided to build his own.
[WilkoL’s] design is composed primarily of an electret microphone, microphone preamplifier, CD4040 binary counter, LM386 audio amplifier, and a speaker. Audio signals are analog and their amplitudes vary based on how close the sound is to the microphone. [WilkoL] wanted to pick up bat sounds as far away as possible, so he cranked up the gain of the microphone preamplifier by quite a bit, essentially railing the amplifiers. Since he mostly cares about the frequency of the sound and not the amplitude, he wasn’t concerned about saturating the transistor output.
The CD4040 then divides the signal by a factor of 16, generating an output signal within the audible frequency range of the human ear. A bat signal of 20 kHz divides down to 1.25 kHz and a bat signal of up to 100 kHz divides down to 6.25 kHz.
He was able to test his bat detector with an ultrasonic range finder and by the noise generated from jingling his keychain (apparently there are some pretty non-audible high-frequency components from jingling keys). He hasn’t yet been able to get a recording of his device picking up bats. It has detected bats on a number of occasions, but he was a bit too late to get it on video.
Anyway, we’re definitely looking forward to seeing the bat detector in action! Who knows, maybe he’ll find Batman.
The real question i have is whether this could be used to repel the locusts that invaded Las Vegas last summer…
Hey, it’s Las Vegas, it’s just the first plague. (Hope you’re not the first born!)
Expecting people to turn into pillars of salt?
I was looking forward to a searchlight with a stencil. This is even better.
We agree!
De bat he rat got wings,
All the chillen know dat.
All I need to know from the Lord,
Is how to get de wings on de cat.
Whatever for?
Elastic and velcro… https://www.aliexpress.com/item/4000252787545.html?
That brought back memories.
Back in the old days, the rare TVs that had remote controls, responded to jingling keys.
… for example, the Zenith “Space Command” remote control. We had one (1960’s), and from the factory, the tuner only handled channels 2-13 (U.S., VHF). If I remember correctly, ít had a provision to add a tuner for UHF (special 14th position on the tuner). The alternative was a Blonder-Tongue UHF adapter. Don’t remember for sure, but I think it output on VHF frequencies.
They were pretty simple- little tuned rods that were hit when you pressed a button. Sort of manual wind chimes.
Was expecting a search light and a metal cut out of a bat for calling The Batman…
Hopefully this device didn’t disappoint :)
Gotta make one!
WilkoL here. Thanks for having my simple detector on Hackaday! It is correct that there aren’t that many bats here, but I have detected bats on several occasions. I just can’t get it recorded…
Hi WilkoL, thanks for the correction! I’ve updated the article accordingly. Let us when you’re able to get a recording. We’re pretty excited to see it.
I just added a “video”with five minutes of almost total darkness and the sound of one or two bats flying around my backyard. See step 4 of the Instructable.
Or just go to the video itself….
https://youtu.be/C1KVKyYYUbI
There was an instrument that HP made a long time ago, called an ultrasonic translator leak detector. The principle was, since the pitch of the sound air going through a small hole makes is inversely proportional to the diameter of the hole, if a leak is small enough, you can’t hear it. So they made this “translator”, which is really just an oscillator and mixer, kind of like a superheterodyne radio, only acoustic. It shifts the spectrum of the sound down by the frequency of the oscillator. Because this doesn’t use counters, the sound doesn’t have to be at digital triggering levels, so it is very sensitive. It had more than one transducer – I think one was a contact probe, and another was a directional microphone, probably not important for bat detection, but real useful for pinpointing (as it were) small gas leaks.
Any references on the HP ultrasonic translator leak detector? A quick Google search reveals HP Delcon 4818, 4917A, 4918A and a 4905A.
Well, the pictures I’m finding for the 4917, 4918, and 4905, all look alike, and look like the instrument I used. But this was 1980 or so, and I don’t remember exactly which model we had. It may be that they differ by how far they translate the signals, for different applications.
But HEY! Here’s a video showing a 4918A in action!
https://www.youtube.com/watch?v=QE-m58nvNOk
I’ve used something similar for finding corona points in HV systems (with an appropriately insulating rubber ‘snoot’).
That basic principle is still in use… with some enhancements:
https://www.fluke.com/en-us/product/industrial-imaging/sonic-industrial-imager-ii900
Awesome edition to the Instructables line of Bat Detectors and very simple too!
The Intelligent Bat Detector was a great recent addition too with some informative comments regarding Shazam, transducers and MEMS. I’ve been reviewing options the last few years and neat communicating with the manufacturers also to see options for making. These portable systems are nice!
For mobile or base station use and recording, I’ve been wanting to invest in the Texas Instruments ADC5140 evaluation board that has a 768kHz sampling rate capability that would be neat to work with… though not quite the performance as the G6. https://www.ti.com/tool/ADC5140EVM-PDK These however aren’t so handheld portable devices which are nice to have as an option especially if you’re not having to scan to ID or pinpoint a signal.
Wouldn’t this also significantly distort the sound by converting it to a square wave?
Yes, but sound quality wasn’t the goal in this one. The output of the divider is a squarewave anyways. I made this one to warn me when bats are around. They are rather rare here and I didn’t want to stare at an empty sky all night. I’m building a heterodyne and dividing detector that should sound better.