First, here are some important precautions. Read and follow them carefully.
As this homemade toy phone is likely to be used by children, these instructions should be carried out by an adult or by a child or children under close, adult supervision. As will be reiterated later, styrofoam cups should substitute the tin cans wherever possible. This should be done especially if there is any question of safety with the metal edges of the cans.
You will need two, clean, empty tin cans, preferably new with no rust or sharp or jagged edges. Remember to substitute the styrofoam cups for the tin cans for safety if you have any doubts. The children will be putting the open ends of these to their ears and mouths.
You will also need a long piece of white kite string, new, with no knots or unraveling.
You will need a clean, new nail just slightly thinner than the kite string you will be using.
You will need a hammer. If you are using the tin cans you may want a forked hammer to pull the nail from the cans when making the holes. If you are using the styrofoam cups you won’t need a hammer and may even be able to use a toothpick for the holes if it is the right size.
How to construct your toy phone
Using the nail and hammer, poke a hole in the center of the still-sealed ends of the open cans. Make sure the open end has the lid completely removed. If you are using the styrofoam cups, simply use the nail or a toothpick to press the hole at the bottom of each cup. Now, run the string through the hole in the can or cup. Tie a knot in the string at the end inside the can or cup. You should have a can or cup with the string knotted inside and the string running to the other can or cup and knotted inside in the same way. The knots need to be at the very ends of the string.
To use the phone each user should have one can or cup and be far enough apart to draw the string uptight. While one party is talking into their can or cup the other should have theirs to their ear to listen. If you can’t hear the other party, the string isn’t drawn up tight enough, the holes in the cans or cups are too big, or you have the wrong string. You need to also make sure you have a tight seal around your mouth with the can or cup.
How does it work?
The sound vibrations or “resonance” as it is called is carried down the string to the other cup. The cup acts as a sort of megaphone for the hearer and a sound tunnel for the sender. You will be amazed how well your toy telephone works.