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Offline Paul ATopic starter
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« on: November 02, 2010, 11:57:55 am »
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Yep..... me.....
Sorry if this is in the wrong place... mods feel free to move it.
Anyway,
Couple of years back I built a "Bat Listener" for the amusement of my lad.
(we've got loads of the little bu**ers around the garden)
Ultrasonic transducer - 2 stages of pre-amp - divide by ten chip - audio amp.
Well, it never did work... as soon as it was swiched on it went loopy... all kinds of chirping from the speaker (even if you put the damn thing under several cushions...)
Spent ages messing with it ..... never got it right, so it got thrown in the "junk box" for parts.
Last week my lad announced that he was doing a project at his (new) high school on......bats.......
I dug the "listener" out from the junk box..... the transducer had come off and was hanging from the box by it's wires.
Put a battery on it....and......it worked perfectly!
Much head scratching later i realised why.....
Where the transducer was mounted on the box it was causing "feedback" !
Now it was just hanging on wires ...... no feedback!
It's mounted back on the box now, but seperated by mucho foam!
Perfect!
But...... do I feel stoopid.......


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Offline GoldDigger1950
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« Reply #1 on: November 02, 2010, 12:00:05 pm »
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Isn't it just so amazing how accurate hindsight really is?

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« Reply #2 on: November 02, 2010, 12:45:11 pm »
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Weird!   I was just looking at one of those the other day.

My Need was to check Geodes.

I was thinking if I Placed the Transducer to a Geode and tapped it with a metal rod, I could hear if it had a cavity or not.





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Offline mdiede57
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« Reply #3 on: November 02, 2010, 01:58:22 pm »
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you shoudl put a schematic up of your project, I think people would have fun with it.

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Offline seldom
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« Reply #4 on: November 02, 2010, 02:00:32 pm »
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Quote:Posted by homefire
Weird!   I was just looking at one of those the other day.

My Need was to check Geodes.

I was thinking if I Placed the Transducer to a Geode and tapped it with a metal rod, I could hear if it had a cavity or not.






Thats interesting Home are you going to try it?

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« Reply #5 on: November 02, 2010, 02:16:55 pm »
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They are actually quite useful....
Not only can you hear "bats" but you can "hear" if a high voltage circuit is working.
You can also find tiny punctures in tyres and inner tubes as the air escaping makes very high frequency sound.
Dunno about the geode thing.... don't see why not though.. I'll give it a try as we've got a few "thunder eggs" that haven't been cracked open.
I'll dig around my cd's which I'm sure have the schematic on and post it (it's a dead easy build).


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« Reply #6 on: November 02, 2010, 04:25:45 pm »
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I'm given to understand that the ultrasonic range of a bat listener can also detect a termite nest from a great distance.

Posted on: November 03, 2010, 12:55:48 AM
Here's one that looks pretty easy.

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It looks to me as if you could add a small rotary switch to increase the ultrasonic range to include hummingbird wings, a mosquito in the room and maybe even the ultrasonic crackle that comes just before a lighting strike.

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« Reply #7 on: November 02, 2010, 06:11:06 pm »
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Cool, If it works there would be a limited market for them here on the Rock Hound Roundup Rock show.



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« Reply #8 on: November 03, 2010, 01:54:54 am »
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Quote:Posted by GoldDigger1950
I'm given to understand that the ultrasonic range of a bat listener can also detect a termite nest from a great distance.

Posted on: November 03, 2010, 12:55:48 AM
Here's one that looks pretty easy.

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It looks to me as if you could add a small rotary switch to increase the ultrasonic range to include hummingbird wings, a mosquito in the room and maybe even the ultrasonic crackle that comes just before a lighting strike.


That's the one I used!
Only I added a third amp to drive the audio to a speaker.....
That was my mistake! it was also what added all the feedback.....
It's a very good little circuit VERY sensitive .......
Stick with the earphones and don't get all fancy like I tried and It'll be good!
Actually the range is pretty good... shouldn't need a switch.
GO FOR IT!
 Cheesy


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Offline GoldDigger1950
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« Reply #9 on: November 03, 2010, 08:39:03 am »
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Paul, I was referring to extending the range of frequencies, not the detection range. The transducer is center tuned to 40khz and divided digitally. By switching between the divisors, you can extend the range of frequencies that it can sense. Anything above and below the 40khz will not be as strong as the center frequency but it will allow other ultrasonic listening.

All in all, a great looking little project that might be useful for non destructive geode 'cracking' as has been suggested.

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Let's Talk Treasure!
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