Prof. Tom Perera - W 1 T P - Historian and Collector


The Electric Telegraph is one of the most important inventions in the history of science ! It directly led the way to the development of all digital communications including computers, fax, the internet, email, and text messaging.

I am often asked for help in building a working electric telegraph set for use in school projects, science fairs, displays and demonstrations.

I have tried to outline the process of building a simple telegraph set in the paragraphs below and I have included several variations as well as a simple wireless telegraph set.

Before you start to build a telegraph set, I STRONGLY SUGGEST that you read HOW A TELEGRAPH SET WORKS.
This LINK describes the THEORY and OPERATION of the "electric telegraph".(4KB)


Many people have inquired about how to build a simple telegraph system to approximate the early systems used in the 19th century. You can view thousands of pictures of telegraph sets in my main telegraph museum:

Here is a photo of one homemade key and sounder that was build to look just like some of the telegraph sets that were used from 1844 to the 1950s:

As you can see, this was a carefully thought-out and executed project.

Many people just want to build a very simple set to become familiar with the basic principles of the electric telegraph.

The following project is the simplest functional telegraph system construction project that I could design. It requires very few parts and all of them should be commonly available.

The project uses readily available parts:



Construction of the telegraph set is very simple. Just look at the photographs and you will see how it is put together.


If children will be using the set, you will want to round all sharp corners with a file or sandpaper and perhaps put tape over any exposed sharp edges.

The key is made by screwing one of the strips of metal to one of the pieces of wood so that pushing down on the strip brings the strip into electrical contact with the screw that is mounted under it.

The Battery Holder: is made by screwing two of the metal strips to the wood so that they can make electrical contact with each end of the lineup of the two batteries. A rubber-band may be used to maintain pressure on the battery contacts.,br>

Be sure to put the batteries in the holder with the positive tip of one battery pushing against the negative bottom of the other battery. This is called a "series connection" of the batteries and adds the 1.5 volt voltage of one battery to the 1.5 volt voltage of the other battery to produce a total of 3 volts. Most flashlights are designed this way.

The Sounder: requires a bit of care in construction and adjustment.

The electromagnet coil consists of one of the iron nails with at least 100 turns of the wire wound neatly around it. ( If possible wind on 200 or more turns to make the magnetic force stronger. )

The longer iron-bearing strip of metal is screwed to the wooden base and bent so that it extends up and over the top of the nail. This piece has been labeled "IRON-BEARING" in the parts photograph to indicate that it is pulled in by the magnet. Many food cans are made of this type of metal. Be careful not to cut yourself on any sharp edges.

When the electric current passes through the coil of wire, it makes the nail into an electromagnet which pulls the strip of metal down to the nail and makes a clicking sound. (You may have to carefully adjust the strip of metal so it is close enough to the nail allow it to be pulled down by the magnet.)

The second nail is important because it keeps the strip of metal from pulling too far away from the electromagnet. It also serves to make a clicking sound when the strip of metal is released by the magnet and moves upward.

To complete the telegraph set, simply connect the key, batteries, and sounder with the wires as shown in the first picture.

When the coil is deenergized by opening the telegraph key, some stored electricity is released.
It is possible to receive an electric shock if you are touching both of the contacts of the key with your fingers while you release the key.
(This can not happen if you build the telegraph key as shown in the pictures because the bottom contact can not be touched while pressing the key down.)

There are two ways to eliminate this problem:

1. Make it impossible to touch the lower contact of the key.
The key in the pictures has a lower contact that is covered by the top contact and it is not possible to touch it at the same time that the top of the key is being pressed.

2. Place a diode between the two contacts on the key. Radio Shack sells a diode that will absorb the electricity when the key is released. The Radio Shack part numbers for appropriate diodes are: 276-1101, 276-1102, 276-1102 or 276-1104 and they cost about $ 1.00.
Just connect the two wires of the diode to the two contacts on the telegraph key with the white band on the diode being connected to the side of the key that is connected to the positive (+) side of the battery. If you have connected the diode incorrectly, opening the key will not open the circuit. In that case, simply reverse the diode connections.


When you push down on the telegraph key it completes the electrical circuit from the key to one end of the coil and from the other end of the coil to one end of the battery and from the other terminal of the battery back to the other side of the key.
Now the sounder magnet should pull down the metal strip and make a CLICKING sound. When you release the key, the metal strip should spring upwards and make a CLACKING sound.
(If it does not work, please see the "Troublshooting section below.)

You can learn to tell the difference between the dots and the dashes of the Morse code by learning to tell the difference between the pull-in "CLICK" and the release-"CLACK".

The pull-in "CLICK" is the sound the metal strip makes when it is pulled in by the electromagnet coil and strikes the nail which is in the center of the coil.

The release "CLACK" is the sound that the metal strip makes when it is no longer pulled by the electromagnet coil and it moves rapidly upward to strike the upper nail.

The Morse Code Characters are called DOTS (or 'dits') and DASHES (or 'dahs') They are made from the CLICKS and CLACKS as follows:

A DOT is created when there is just a LITTLE time between the pull-in CLICK and the release CLACK.
Try it now: Push the key and quickly release it.
Did you hear the CLICK followed quickly by the CLACK ?
That was a DOT in Morse code.

A DASH is created when there is a LONGER time between the pull-in CLICK and the release CLACK.
Try it now: Push the key and after a short wait, release it.
Did you hear the CLICK followed after a short wait by the CLACK ?
That was a DASH in Morse code.

Now let's send the letter "A".
In Morse Code, the letter "A" is: DOT DASH. (or Dit Dah).
Push down the key and release it quickly to make a DOT and then push down the key, wait a bit, and release it to make a DASH.
Try it! You have just sent the Morse Code letter "A".

Now let's send your name in Morse Code:
Find the letters in your name in this Morse Code table that shows the dot and dash equivalents of letters and numbers in the American Morse Code and the International code:
(The American Morse Code was mostly used by the railroads and the International code was used for wireless and radiotelegraphy and in foreign lands.)


Here is another version of this set:
It was made by 13 year-old Claire Berry in KwaZulu-Natal, South Africa. It won a high grade in a science project.

Here is another version of this set:

This is a closeup view of the sounder:

Here is a third version of this set:

***!!DO NOT MAKE A TELEGRAPH SET LIKE THIS ONE !!! This young builder has made the set with wire that has NO INSULATION on it. Each turn of the coil short-circuits to every other turn on the coil so the magnet does not work at all. Please use WELL INSULATED WIRE when you wind the coil.

Here is an excellent Telegraph Science Project by 5th. Grader Katie:

Here is an American 5th. grade student named Jasiah and the science fair project that won him first place in his school's Science Fair. He will be entering it in the County Science Fair in the Spring of 2015:

Here are three students practicing with their homemade telegraph set at a school in England:

An Excellent Modification of my Basic Design by Rahul Sharma:

15 year-old Rahul Sharma in India designed and constructed a system that uses a pencil to write dots and dashes on an electric motor-driven moving paper tape. This makes it easier to read the Morse Coded letters visually and does not require training in listening to a sounder. He recreated the very first method of recording the Morse code message on a paper tape as it was invented and used by Alfred Vail and Samual Morse. He writes: "I modified your design a little. Instead of a metal strip I made something like a see-saw with ice cream sticks and mounted a metal scale on it. It was much more difficult to make but it gave better results. Also, I installed a register to copy down the code." Here is a picture of Rahul's telegraph set: Nice job, Rahul...


You may use up to 100 feet of wire between the key and the sounder.

Please be careful not to hurt yourself while building this set. The improper use of tools during construction can cause serious injury. The original designer of the set and the maintainer of this web page accept no liability for injuries caused by the construction or operation of the set.

Here is the circuit diagram of the completed telegraph set:
The components are all in what is called a 'series circuit'. When the key is closed, the electricity flows in 'series' from the batteries through the closed key to the sounder and through the sounder coil back to the other terminal on the batteries.
(The 2 batteries are combined

     !             !
     !          BATTERY 1
     !             !

And Here is one of the circuits which will allow two of these sets
to be hooked together to send messages to a distant friend. You may
use up to about 100 feet of wire to connect to the other set:

This is the circuit which was used in the early land-line telegraph
stations.  Please NOTE that ONE KEY must be in the 'closed' position 
in order for the other key to operate the sounders.  Most of the 
early keys had a built-in shorting switch to keep the key circuit
closed and make it possible to receive messages.  One advantage of 
this circuit is that the battery can be at either end of the wire 
or even in the middle.
                        Wires to other set:
     !                                                    !
  SOUNDER                                              SOUNDER
     !    SET 1.                                 Set 2.   !
                        Wires to other set:

*** NOTE: ONE key MUST be kept CLOSED in order for the other to work. ***

Here is another circuit which was designed by Bill Horne, W1AC.
The advantage of this circuit is that it allows either key 
to operate the sounders at any time without wearing down the batteries and 
without the need to close the circuit closing switches on the keys.  
NOTE: For this circuit to work, It IS IMPORTANT to wire the batteries with 
the POSITIVE (+) and NEGATIVE (-) Terminals as shown.
If you do not do this, the sounders will close as soon 
as they are connected. 
NOTE: It is also IMPORTANT to use the same voltage..
( ..for example, 2 D-cell batteries.. ) for each battery.

                        Wires to other set:
   + ! +             !                      !             + ! +
  BATTERY           KEY                    KEY           BATTERY
   - ! -  SET 1.     !                      !    Set 2.   - ! -
                        Wires to other set:



Overheating and dead batteries {CAUSED BY USING UNINSULATED WIRES)
One parent emailed that all his completed set did was to have the coil of wire get very hot and that the batteries went dead shortly afterwards.

After asking him a few questions, I found out that he had wound bare (uninsulated) wire around the nail. I explained that the coil of wire had to be made from insulated wire so that the individual turns in the coil did not electrically connect to each other.

Sticking Sounder Won't release quickly or at all
One parent noted that closing the key caused the electromagnet to attract the metal armiture of the sounder but that it did not release after the circuit was opened.

I suggested increasing the strength of the springiness of the metal that pulled the armiture away from the nail...
..... AND
INSERTING a very thin piece of plastic sheeting or wrapping materal between the nail and the armiture to prevent the metal armiture from directly coming into contact with the nail.

Can't tell the differece between a CLICK and a CLACK
Try using a different metal nail as the upper 'stop'.
Try putting a bit of aluminum foil on the upper stop to change the sound of the release CLACK.

There are many ways that you can modify this basic circuit.

For instance, you could put a flashlight bulb or a 3-volt sounder or buzzer in the series circuit so it would flash or buzz in addition to clicking when you close the key.
This might help some people to learn to copy the Morse Code more easily.

You could also mount a pencil on the sounder arm and have it mark a piece of paper with either a high mark or a low mark while the paper was pulled under the pencil at an approximately constant speed. This would work exactly like Samual Morse's very first telegraph systems that were used before people learned to copy the Morse Code by ear. Morse invented what he called a "register" which used a clockwork mechanism to pull a paper tape under a pencil which was moved in and out by an electromagnet.

If you use this system it is quite easy to translate the short or long downwards pencil marks on the paper into dots and dashes. Registers were used to make Morse Code marks on paper tape right up to the time of the American Civil war when people finally discvered they could copy Morse Code by ear. President Abraham Lincoln had a telegraph office that kept him informed of the progress of the Civil War by receiving telegraph messages from his generals in the fields of battle.

Good Luck with your projects...


Explanation of how the telegraph works:


Please click on the following link if you would like to build:
A simple working wireless telegraph set:(15KB)


If you already have an old telegraph sounder and would like to have it operate in response to audio tones such as those from a code practice oscillator or short wave receiver, you will find a simple circuit diagram at this link:
A simple circuit for driving a telegraph sounder from audio tones:(20KB)



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Professor Tom Perera Ph. D. - W1TP
Professor Emeritus:
Montclair State University
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