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

( I am always looking to buy or trade telegraph keys ! )


I am often asked for help in building a working electric telegraph set for use in school projects or displays and demonstrations.
I have tried to outline the process of building a simple set in the paragraphs below and I have included several variations as well as a simple wireless telegraph set.
If you decide to build a telegraph set, I would particularly appreciate receiving photographs of your completed set and I will try to post some of them on this page for other "telegraph builders" to see.

Before you start to build a telegraph set, I suggest that you read about the way that their design developed and about how a telegraph set works. This LINK describes the THEORY and CONSTRUCTION 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.

Here is a photo of one homemade key and sounder:

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 find. It requires very few parts and all of them should be commonly available.

The project uses readily available parts:(12KB)

Construction of the telegraph set is very simple. Just look at the photographs and you will see how it is put together. Be careful not to cut yourself on the edges of the metal strips. If children will be using the set, you will want to round all sharp corners and perhaps put tape over any exposed sharp edges.

The key:(14KB) 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:(14KB) 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.

The Sounder:(12KB) 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 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.

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.

Here is another version of this set:(24KB)
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:(29KB)

This is a closeup view of the sounder:(36KB)

Here is a third version of this set:(37KB)

Here is an excellent Telegraph Science Project by 5th. Grader Katie:(50KB)

If you would like a listing of the dot and dash equivalents of letters and numbers in the American Morse Code and the International code, select the following link:

The American Morse Code and the International code:(2KB)

Simply connect the key, batteries, and sounder with wires as shown in the first picture.
Pressing the telegraph key completes the electrical circuit and allows electricity from the battery to flow through the sounder's coil and it makes a clicking sound as the metal strip strikes the nail in the center of the coil.
Releasing the telegraph key allows the metal strip to spring upwards and strike the other nail, making a different click.
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 battery through the closed key to the sounder and through the sounder coil back to the other terminal on the battery.

     !             !
     !             !

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 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: 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:



One resourceful parent who was trying to plan a simple telegraph project for 64 children writes:

"I built a prototype using two strips of sheet metal screwed down to a piece of wood for the switch or key to switch the electricity on or off."

"I used a nail as the core of my electromagnet and I wound 100 turns of insulated wire around the nail. I mounted the nail so that it would attract a piece of springy iron when it was activated. (at first, I used a piece of aluminum or copper metal and discovered that the metal had to be iron or ferrous metal for the magnet to be able to pull on it)."

"I connected them all as in your diagram and used a battery holder and two "D" size flashlight batteries to provide the voltage."

"When I push the key, it brings the two pieces of metal together and completes the electrical circuit. The electromagnet then pulls in the piece of springy iron and it makes a nice click."

"I can't figure out how to differentiate between a dot and a dash when all I get is a click". (All he needs to do is to put a second piece of metal up OVER the piece of springy sheet metal of the sounder to make a second click. when the sounder releases, and he will have made a complete replica telegraph system. - - see detailed explanation below - -)

"I built another prototype hooking a buzzer to the circuit instead of the sounder. That took care of the problem of telling the difference between a dot and a dash, but it isn't much of a challenge or learning experience for the kids."

"Any help or suggestions would be appreciated."


I replied:

What a great project! Congratulations on creating a working system like that... Yes, It is easier to have the kids learn to use a buzzer than to use a clicking "sounder". A doorbell buzzer, available in hardware stores approximates the early buzzer sounds quite well.

The sounders used from 1850-1950 were like your nail/solenoid.... IF... you were to modify it by putting a piece of metal OVER the piece of sheet metal that is moved by the electromagnet. This would give you a system that made a click when the electromagnet pulled IN and a slightly different clack when the electromagnet released.

Sounders all make a slightly different sound when they pull-in rather than release and the operator learns to discriminate between these two different sounds and soon unconsciously can tell a dot from a dash.
Click-in..clack-out is a dot.
Click-in..............clack-out is a dash.

That might be a bit of a challenge for your kids to learn so you might want to go to the buzzer system used from about 1910 to 1950.

You could also try using very different metal parts to strike on the pull-in and release to make the sound difference even more noticeable.

You could also use a light bulb as an adjunct to the sounder and have it go on whenever the sounder was activated. This might help the kids learn to copy the code.

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 approximate Samual Morse's very first telegraph systems used before people learned to copy code by ear. Morse invented 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 used this system, the kids could translate the short downwards pencil marks on the paper as dots... and the long downwards pencil marks on the paper as dashes...

Good luck with your project.


Overheating and dead batteries

One parent emailed that all his completed set did was to have the coil of wire get very hot and that the battery 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:

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.

PLEASE let me know if you have problems or solutions that might be of interest to other builders...

Good Luck with your project... and don't forget to send pictures...


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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