Bat Detector

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Bat Detector

Post by bwts » Sat Apr 12, 2003 4:49 am

I think somebody has posted something on this B4. Anyhow I want to pick up bat sounds and convert them to an audiable signal.
1) Do I need a special microphone?
2) How would I divide (?) the frequency to bring the ultra sonic signals into the audio range?<p>Tx B)
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Re: Bat Detector

Post by Dimbulb » Sat Apr 12, 2003 7:55 pm

An ultrasonic mic goes a two stage op-amp
output is divided by sixteen.
approximately in the bat world there are a vaiety of frequencies.
37.8Khz divided by 16 = 2.36 Khz
40.2Khz divided by 16 = 2.51 Khz<p>

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Re: Bat Detector

Post by russlk » Sat Apr 12, 2003 9:03 pm

I built a device like that to listen to ultrasonic alarm sounds. It used hetrodyning to bring the sound down to audible levels. The "microphone" was an ultrasonic transducer used in an alarm system. I hooked it up to an oscillator and drove the dog crazy. It is interesting, what the dog hears. I probably still have a transducer, I will look for it if you are interested.<p>I might be able to find the schematic from 30+ years ago also.<p>[ April 12, 2003: Message edited by: Russ Kincaid ]</p>

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Re: Bat Detector

Post by hamsterears » Sun Apr 13, 2003 3:46 am

Please note, I've built the circuit indicated by the post above. It does work, and fairly well.<p>You can use a "Walkman" type headset, instead of the crystal earphone indicated.<p>Otherwise, there are two types of bat detector. Frequency dividers, and heterodyne. Each has it's advantages and disadvantages.<p>The frequency divider circuits are generally easier and cheaper to build. They also work on a wide range of frequencies at once.<p>However, you tend to lose all the amplitude (loudness) information, so a bat on the edge of detection range sounds just as loud as one right in front of the microphone. This means that a call that sounds like beep-beep-BEEP-beep becomes beep-beep-beep-beep. No variation in loudness.<p>Heterodyne detectors retain the amplitude information. However, since they work on a frequency subtraction principle, they can miss stuff you'd pick up with a frequency divider unit.<p>For example, if you've set your frequency to 45khz to pick up species "X", and a bat from species "Y" flys by making 75khz noises, then 75khz - 45khz = 30khz, which is still outside human hearing range. So you won't hear it.<p>Also, since the relative frequencies stay the same, a bat with a range of sound greater than 20khz will still produce sounds outside the human hearing range. (I don't know if there are bats with that much range, but it's possible).<p>If you search the web for the term "Bat Detector", you'll find a lot of plans for both types of detector, as well as complete units of both types. Deciding which you want depends on what you need.<p>Michael Fagan

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Re: Bat Detector

Post by jimmy101 » Sat Jun 23, 2012 11:46 am

It should be pretty easy to make a detector that is both heterodyne and digital. For the heterodyne circuit in the 2011 N&V you would just need to add a digital divide chip (e.g., CD4024B) and perhaps a single resistor to limit the output to the ear piece. Put a DPST switch in that shunts the amplifier's output to either the mixer opamp input (heterodyne detection) or to the CD4024B CLK input (digital detection).

The power supply might have to be boosted to a 9V battery since I believe the CD4024B would be a bit marginal at 3V.

EDIT: Or, use the switch to select which of the two outputs (heterodyne's mixer opamp vs. CD4024B output) is routed to the headphone. The CD4024B and the mixer opamp should both be able to be connected to the amp's output all the time.

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Re: Bat Detector

Post by Externet » Sun Jun 24, 2012 9:51 am

I would use a NE602 ic
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Re: Bat Detector

Post by haklesup » Tue Jun 26, 2012 12:44 pm

Getting the bat to fly where you want it to is easier than you think. Just toss a pebble in front of its flight path and most often it will follow it almost to the ground thinking it is a fat jucy bug. This is the best way to get them to leave a room. With the right orientation to the mic, you should be able to record some nice homing signals

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