Intro: Magnet Powered Telephone
This instructable will progressively show how to make at least one kind of telephone that sounds good enough to be fun and useful, without requiring batteries, AC utility company power, or utility telephone services.
I suppose it may be most appreciated by smart young children with "forts".
Step 1: Things You Will Need
Since I have done this before I know that the following supplies will be needed:
Two SMALL transistor radio speakers with BIG MAGNETS. Usually they are 8 ohms,
... higher resistance would be better, they could be (rare) 16, 32, 45, 100, or 600 ohms
as long as they are both the same ohms resistance.
The speaker size is almost perfect if both of them can hide under a CD. Bigger is not better.
Wire... Telephone wire or computer network wire or extension cord wire WITHOUT PLUGS.
Optional but very effective... some things like horns or cones.
I suppose you could use cans instead of horns.
But I'll try to show how to make a horn like those ancient wind up groovy-disc music boxes have.
Optional for long distance... high impedance matching transformer such as used in PA systems,
or which are designed for tube or transistor radios to match 8 ohm speakers to 1,000 or 10,000 ohm
amplifiers. Such transformers are also used in some speakers in systems for playing
background music and paging in supermarkets.
Distance is limited by how much wire you have and how far you can run it without annoying anyone,
especially the police.
You don't need all this stuff. Just one long pair of wire and two speakers will be enough.
Step 2: Connect 2 Speakers to the Ends of the Wire
Well you might want to run the wire first at least into the next room and find someone to talk to.
If you have no friends, turn on the video and the news, they usually talk a lot.
Then put the speaker wires on your "telephone wires" like in the picture
and talk and listen to your friend. If it's the video, be sure your "telephone" speaker is near
the video speaker and not a picture tube.
(If you magnetize a picture tube the colors get messed up and that's not good.)
Well this in the picture is the functional part.
When I add more steps they will be improvements mostly to make it pretty.
Like putting it in a box, adding horns, stuff like that.
WOW. Even I'm impressed how loud and clear this is already.
Maybe you'll have to holler on a really long wire but you won't be misunderstood!
I'm thinking that when I put horns on it I'll be able to eavesdrop on the other room.
BUT, If you try to talk to yourself you won't hear yourself.
Definitely get a friend and hook them up in a room that you usually can't hear them in.
And be very careful with the wires not to yank them off unless you can solder and collect speakers like me.
OH, I forgot to mention in case you didn't notice, you talk and listen to the same speaker.
It's used just like a cans-and-string phone, but there are magnets in it too.
Step 3: Make It Look Nice, and Louder Too.
Still working on horn plans. Gramophone type horns are magic the way they can make
really loud sound without any electricity.
The speakers will work better when mounted. There is even a noticeable difference in
loudness if you hold the speaker between your thumb and finger. And if you duct tape
it to the inside of a cardboard box at least. Really beautiful boxes cost more than
the rest of the project so I'd recommend making the box out of wood in antique-radio style
if you really want to use this project a lot and your mate can't stand ugly stuff.
Hot glue around the speaker (definitely avoid gluing the paper speaker cone! ) seems convenient
for mounting a speaker inside a box. I've made corrugated-box speakers before and it should be
obvious that a round hole slightly smaller than the speaker should first be cut in the box,
and optionally a mesh (screen) could protect the speaker from accidentally poking holes in it.
Besides the sort of junk pictured below that you could use as a case, well, someone just made
an instructable about making a decorative speaker out of a tennis ball. Check that out.
In the picture are just a few odd things that could, did, or do have small speakers in them
and could be used in this project.
Step 4: Miscellaneous Ideas About Using Horns, Etc.
At this point in time my plans to build a gramophone horn (for an unrelated project)
looks like it may not be so soon. Essentially I will try to make a cone or flower-shaped one by
cutting a large semicircle and/or long triangle out of copper flashing, bending it into
a cone or creasing it to make an octagonal pyramid shape open at both ends.
And soldering the seam together and perhaps to some copper pipe that goes to
-in this case it would be- the speaker(s). If I do that then I will put a picture of it here.
There are probably many other sources of complete horns, and corrugated paper cardboard
and duct tape is a "el-cheapo" material to make one. Here are some ideas for where to get
Bicycle horn... Large vehicle horn... Broken or toy musical instrument... Traffic cone...
Totally rotten gramophone, or antique telephone or radio...
Actual field telephones that work the same way that this project does...
Surplus american fire sirens that usually consist of a fan with one or more horns around it...
Untried idea... since another instructable used earbuds as microphones, they may work well
with horns. Earbuds may have tiny rare earth magnets and high resistance but my guess is
that they can not handle very much sound.
Untried idea... pair of telephone handsets with only a transistor-radio-speaker at the ear-end
may look and work more phone-like.
The parts that are usually inside the handsets will not be useful for this magnet-powered project.
The use of the transformers mentioned in step 1 are for long-distance lines and I'd imagine them being used
between two large crop farms. What they do is take the low voltage from the speaker and step it up,
and also make the speaker have a much higher resistance than the wire. It's necessary because
if the long wire is more than 8 ohms then it will cause a big loss of volume between two 8 ohm
speakers. But if the speakers are making a higher voltage at a resistance of 1000 or more ohms,
then the wire resistance is of no effect.
WARNING: Actually using these phones over such "long distances" is likely to attract lightning
and accumulate dangerous voltages.