Bubble-Gum phone

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Bubble-Gum phone

Postby caverdoc » Apr 7, 2009 11:02 am

Has anyone ever built a "bubblegum phone" like the ones shown in the Communications portion of NCRC training? I was able to find an article in Speleonics #18 by Frank Reid, "Piezoelectric Sound-powered telephone" that outlines building one using a piezoelectric speaker element (part #273-091 at Radio Shack).

I'm just curious about whether any members have built such a device.

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Re: Bubble-Gum phone

Postby NZcaver » Apr 7, 2009 12:17 pm

Yes, I have built several - including the example shown in the NCRC communications material. :wink:

You want one? You've obviously found instructions to build one (it's VERY simple), but the piezo element to use is RS part number 273-073.

Or perhaps you're interested in something more? I can help with all of the above. Let me know.

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Re: Bubble-Gum phone

Postby caverdoc » Apr 7, 2009 3:18 pm

Jansen
Check your PM's.
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Re: Bubble-Gum phone

Postby NZcaver » Apr 11, 2009 3:30 pm

Here's a follow-up post for anybody else who wishes to make up their own little "Bubble-Gum phone" as shown in the NCRC communications material.

Firstly, know that a BG phone is merely a small piezoelectric element which can work as very basic sound-powered "phone" in a pinch. They can be useful as listening devices and for testing the line over a half mile or so range (if you're lucky). But they certainly don't have the range and clarity of the proper field telephones often used in cave rescue, so I suggest you don't rely on them as an effective substitute.

To build one for yourself, you'll need a couple of parts from Radio Shack. The piezo itself and some wires (preferably with alligator clips on the ends).

Here's the way I've done it. Carefully remove the rear of the piezo element case with a knife or tiny screwdriver. Unsolder the flimsy wires from the element itself, and solder on a couple of wires with alligator clips on the ends. I buy the jumpers in the link above, and cut the wire in the middle. Presto - 2 leads with clips on the end. Cut a small slot in the rear cover for the wires, and glue it back in place. Add a little glue around where the wires enter the case to help secure them and prevent water/mud getting in.

I've heard mounting the piezo in an original bubble gum tin or similar (maybe an Altoids tin) improves the acoustics a little. Or you can create a more compact version like I did, by finding an old 35mm film canister to stuff it in. If you do it that way, take a short length of very thin cord and tie a loop onto the piezo brackets. This allows you to hook the piezo over your ear and listen without holding it.

And that's basically all there is to it. See the photo in my previous post for a visual.
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Re: Bubble-Gum phone

Postby ArCaver » Apr 11, 2009 7:31 pm

What length of run will this work over?
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Re: Bubble-Gum phone

Postby NZcaver » Apr 11, 2009 8:11 pm

ArCaver wrote:What length of run will this work over?

Depends. In my previous post I mentioned these being good for about a half mile or so of range, if you're lucky. That's just a rough estimate.

Using one of these, you should be able to hear conversations from other regular (powered) field telephones easily. However there's a good chance they may not hear you very well, if at all.

Here's the thing. To communicate between two of these units, one person has to hold one right up to their ear and listen carefully while the other speaks very loudly. Think of a pair of tin cans and a string - this is the rudimentary electronic equivalent of that. For each additional device connected to the same length of wire, you lose more and more range. This is because each Bubble-Gum phone or regular field telephone adds resistance to the line, and there are limits to how much power your voice can generate using just a piezoelectric element. The phone wire itself can also contribute to poor performance, especially if it has broken strands, missing insulation, or is laying in water or liquid mud.

Does that answer your question? Basically if you're looking to run a phone line to communicate in a cave, this is not really suitable as a primary communication device. For that you could try obtaining army surplus field telephones, or seeking other alternatives.
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Re: Bubble-Gum phone

Postby ArCaver » Apr 11, 2009 8:19 pm

NZcaver wrote:
ArCaver wrote:What length of run will this work over?

Depends. In my previous post I mentioned these being good for about a half mile or so of range, if you're lucky. That's just a rough estimate.

Using one of these, you should be able to hear conversations from other regular (powered) field telephones easily. However there's a good chance they may not hear you very well, if at all.

Here's the thing. To communicate between two of these units, one person has to hold one right up to their ear and listen carefully while the other speaks very loudly. Think of a pair of tin cans and a string - this is the rudimentary electronic equivalent of that. For each additional device connected to the same length of wire, you lose more and more range. This is because each Bubble-Gum phone or regular field telephone adds resistance to the line, and there are limits to how much power your voice can generate using just a piezoelectric element. The phone wire itself can also contribute to poor performance, especially if it has broken strands, missing insulation, or is laying in water or liquid mud.

Does that answer your question? Basically if you're looking to run a phone line to communicate in a cave, this is not really suitable as a primary communication device. For that you could try obtaining army surplus field telephones, or seeking other alternatives.


Oops! Shoulda read that again. Thanks! What type and gauge wire have you tried it with?
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Re: Bubble-Gum phone

Postby NZcaver » Apr 11, 2009 8:52 pm

ArCaver wrote:Oops! Shoulda read that again. Thanks! What type and gauge wire have you tried it with?

No problem.

The wire most commonly used for cave rescue communications in the US is military surplus WD-1. There are 2 types - the earlier WD-1/TT twisted pair style, and the later WD-1A/TT bonded pair which is more common in most cave rescue caches. This wire is not the most highly conductive option, but it's used because it's strong and durable and survives rough handling well. Each of the two conductors contain 4 strands of tinned copper and 3 strands of galvanized steel. These 7 strands have a combined diameter slightly larger than 20 gauge wire. The insulation is black high-density polyethylene. More specs than you ever wanted to know can be found here.
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