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.

Comments

[vitruvian8807]

does this actually work? have any of you people posting "cool" comments actually tried it? I'm just wondering, don't get me wrong, but i can't see how this would actually work without batteries, and magnets couldn't (i think) supply power just sitting there.

[slack-man]

The official term is "Sound Powered Phones". They are used on naval vessels for emergency communications, as no power is required.

I built them as a kid, using both terephone "receivers" and transistor radio speakers.

[pharoah]

Yes... The magnets are not supplying power "just sitting there", that's the whole point. Instead, they supply power only when the coil attached to the diaphram of the speaker is moved by your voice, creating electrical current in tune with the amplitude and frequency of the sound waves. This is reproduced at the other end using the opposite process.

[vitruvian8807]

hmm, how in the world did I miss that?

[epadgett]

:/
I am using two normal 8 ohm speakers and it does not work, could it be something to do with the length of the wires between? The length of the wire is about 10 inches.
Help would be appreciated

[mrdovie]

I've been known to cut the tops off 1 & 2 liter soda bottles for horns, I mostly use them on microphones, but they work as speakers too. Dad's Root Beer has a nice brown color. See my instructable on a blue light blocker mask. These bottles can be used by themselves or used as a mold to make a paper machet horn. An earphone is the right size to drive a soda bottle horn.

[johnpoole]

a little longer the wwii.. look up the ee-8 sound powered handset (called the double e eight) with only slash wire between gun placements we had "acceptable" com.. that was a basic speaker for a transmitter.. your voice moved the small cone, that moved a coil over a fixed magnet.. no batteries, .. way before chips or even transistors made it to the field, great weekend project.. that unit had a hand squeezed generator (90v, 20 mil) that moved a fixed mag on the far end showing white through a small window.. i want to say we did hear the 20 cycle ring through the rec on the far end..

[wobbler]

I used to do this as a kid with old phones. You can just get some old phones and just take out the earpieces. You won't use the microphone so you'll actually need four handsets to make two phones. These are already high impedance and won't need any transformers. Simply connect two earpieces together and when you talk into on it generates a voltage which you can hear in the other one. It will work both ways (Over!) but as you've already go a couple of handsets, you can make up a phone-phone handset by replacing the microphone with another earpiece, which you cross wire to the earpiece of the other handset. Old fashioned handsets where both the earpiece and mic are the same size would obviously be easier. They will work with a reasonable sound level.

[Axie2320]

so awsum!!! im only thirteen, but it sounds like a great project. i love electronics!!!

[rocketman221]

well it works but it is very hard to hear. i always used a pair of portable tape decks, the ones you could get for $1.99. i would hook up a mic to the play head and a speaker to the headphone jack and wire them together with 4 conductor phone/intercom wire. it worked well even with several hundred feet of wire between them.

[mashedpotato13]

Oi! Copycat!http://www.sciencetoymaker.org/SpeakPhone/index.html

[csmiler]

I dont get it...do both of them need to be able to hide under a cd or 1 atta time?

[drcurzon]

1 at a time

[leaterking]

i don't see the next step

[maker12]

ring ring magnet phone {does not sound as good as bananphone!]

[dunnos]

try magnetto phone

[maker12]

good one! ring ring ring magnetto phone

[Crash2108]

Old school simple electronics. I learned this on some show from the 60's.. Forget what is was called. Had a British host.

[iq_abyss]

Dr. Who? (he has taught me tons!)

[VIRON]

Well I have to work up slowly to the PMM. They don't teach this stuff in new school.

[maker12]

BUMER THATS WHY WE HAILL GEAKS!

[RyanPotter]

Wow... So amazingly simple, and so effective! Great idea! And better yet, it can be built with parts that any good geek's got lying around! It makes me want to rig something up so you can talt to a bunch of people at once! Awesome.

[maker12]

easy all you need is 1 fet, a transformer like the ones on telco POTS lines,like radioshack part no 273-1374 and part no 273-1380.

[TheCheese9921]

thats totaly rad dude is there like a way you could do this with a phone and make it ring???

[VIRON]

With this project you could hack a bell-less electronic ringer from a cheap phone to ring thru the speakers. Then it starts needing electricity, unless you can make a crankable generator that produces the sound of ringing. Most american landline phones can be connected in series with 48V about 20 milliamps to talk to each other, and 90 Volts 20Hz(!)AC on the line makes them ring. They may work differently on the other side of the planet, I don't know.

[Myself]

The resistance of the phone and the local loop means that, even though the central office is supplying 48 volts, the terminal voltage across the phone is closer to 10 or 20. It doesn't take much. The 48v DC is called "talk battery", by the way. An old phone tech trick is to create a "talk path" from 2 phones and a 9v battery, very similar to what you've done here, but with some power so the microphones work and the volume level is useful in a noisy office. I've done this lots of times, when I'm on a different floor of the building from someone I'm working with, and there happens to be an unused pair of wires running between floors. Simply connect the battery in series with the two phones, so current runs in a loop: from the battery, into phone A, out of phone A, into phone B, out of phone B, and back to the battery. Take both phones "off hook" and you should be able to talk between them over quite a distance -- depending on the wire you're using, a 9v battery should be good for a few hundred feet. If there are two treehouses/forts not too far from each other, such a talk path is a good complement to walkie-talkies, principally because the "enemy" would need physical access to eavesdrop. Ahh, tactics.

[James (pseudo-geek)]

lol cool. I'll look into building one of those.

[cheezstake]

The US Navy has been using this method since before WWII. Nice and simple instructable.