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The Telegraph Key

The Telegraph Key

Introduction: (Initial Observation)


The telegraph was the only long distance instant communication device until radio and other means came along. Railroads were always the largest users of the telegraph and utilized them for more than a century. The railroads would have had a very hard time operating safely and efficiently without them.

The telegraph key Samuel Morse used on his first line in 1844 was very simple–a strip of spring steel that could be pressed against a metal contact such as a screw. What Morse initially used can be similar to what you see in this picture.

Alfred Vail, Morse’s partner, designed this key, in which the gap was more easily adjustable because of changes in its spring tension. It was used on the expanding telegraph system, perhaps as early as the fall of 1844 and certainly by 1845.

Many manufacturers then started to design and build telegraph keys that offered more comfort and less muscle stress to operators. In this project we will review the telegraph keys made in the past and attempt to build a working model of a telegraph key.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about telegraph keys. Read books, magazines or ask professionals who might know in order to learn about telegraph keys. Keep track of where you got your information from.

Make sure that you visit The Sparks Telegraph Key Review with hundreds of photos and designs of telegraph keys.

What is a telegraph system?

A telegraph system is basically an electrical circuit consisting of 3 parts, all hooked together by a wire.

A battery supplied the electricity or voltage. A key was used to complete or break the circuit. At the distant part of the wire was an electricity detector or electromagnet consisting of a coil of wire which pulled on a piece of metal when electricity was passed through it. (More on this “electromagnet” in a moment.)

The circuit is shown below: (The lines indicate the wires and the arrowheads show the path of the electrical current as it flows through the wires.)

Key: Completes or breaks the electric circuit.
Electromagnet: Pulls on a piece of metal
Battery: Supplies the voltage

The wires were usually made of copper because it conducted electricity better than other metals. It was discovered in the 1830’s that the second wire could be eliminated by using the earth as an electrical conductor. From that time on, only a single wire was necessary to cover the distance between a key and an electromagnet.

The BATTERY consisted of a glass jar filled with a chemical solution (often Copper Sulfate) with copper and zinc electrodes immersed in the solution. A chemical reaction between the electrodes and the solution produced the electrical voltage. The voltage of each cell measured about 1 volt and several cells could be hooked together to produce higher voltages. These batteries produced voltages similar to the dry batteries that we use in flashlights.

The KEY originally consisted of two pieces of brass or copper which could be pressed together to complete the electrical circuit or allowed to spring apart using their natural “springiness” to break the circuit. As people developed the need to send messages more rapidly, the designs of keys changed and the evolution of these different designs of telegraph keys is the focus of my telegraph museum exhibits.

The ELECTROMAGNET consisted of a coil of from 50 to several hundred turns of insulated wire wrapped around an iron core. It pulled on a piece of iron whenever an electric current was passed through it. These devices first caused marks to be made on a paper tape and then, when it was discovered that people could decipher the noises that they made by ear, they developed into the electromagnetically operated “sounders” used from the 1850s to the 1950s.

This is another simple design key .

Click on the picture to see a larger image. Or click here for a different view.

The International Morse Code is a system of dots and dashes that can be used to send messages by a flash lamp, telegraph key, or other rhythmic device such as a tapping finger. As a telegraph key is moved up and down, it makes or breaks an electric circuit and transmits a signal as a series of electric pulses. The telegraph was invented by Samuel Morse in 1837. In the International Morse Code, each letter or number is represented by a combination of dashes and dots. A dash is equal to three dots in duration. A famous Morse Code signal signifies distress: dot dot dot dash dash dash dot dot dot (SOS).

A telegraph set (key and sounder )

What’s a Bug?

The telegraph key was invented in 1844 by Samuel Morse’s associate, Alfred Vail, and was called the “Vail Correspondent”. It was basically a switch with a knob mounted on a spring-loaded lever. The design evolved somewhat until the modern design was invented and patented by Jesse Bunnell in 1881. He called his key the “Triumph Key.”

However, many telegraph operators who used a key for long periods of time developed a debilitating problem, which they called “glass arm.” Today the same type of problem has a kinder name — “Repetitive Motion Disorder,” or RMD. Carpal Tunnel Syndrome is one type of RMD.

In 1902, Horace G. Martin, a New York inventor, patented the first semi-automatic telegraph key, which he began to manufacture as the “Autoplex.” Using a battery and coil like those in an electric bell, the Autoplex made endless strings of dots when the operator pushed a lever in one direction. Dashes were made manually by pushing the lever the other way. Since only dots were made automatically, the key was called a semi-automatic key. Unfortunately, the Autoplex required a separate battery and was probably fairly expensive.

Two years later, on May 7, 1904, Martin filed a patent for a completely mechanical semi-automatic key, which he named the “Vibroplex.” The Vibroplex was based on a lever that rotated around a vertical pivot. Pushing a paddle mounted on one end of the lever to the right and holding it there caused a spring-mounted contact on the other end of the lever to vibrate against a stationary contact, making strings of dots. Dashes were made manually by pushing the lever to the left and releasing it.

Martin was probably not the sole inventor of the semi-automatic key. William O. Coffe of Cleveland patented a mechanical semi-automatic key with a vertical pendulum on January 11, 1904. He must not have sold many copies of his “Mecograph” with the vertical pendulum, because only one is known to exist today. However, he made and sold a number of Mecographs in several different versions with horizontal pendulums.

The Vibroplex did help telegraphers avoid RMD, but it also helped them send faster, which meant they earned more money, since telegraphers were generally paid by the word. Within about ten years, the Vibroplex and a number of clones made by others became very popular.

In those days a poor telegraph operator was called a “bug,” and some operators bought a key from Vibroplex or a competitor and started using it without much practice. The result was poor sending, and the keys themselves became known as “bugs.”

The Vibroplex Company has made a variety of bugs during its long history. Some models are unusual, some are scarce, and some are common. Several other manufacturers made clones and copies of Vibroplexes, some legal and some illegal. Some of the people involved are interesting and colorful, including Martin himself and J. E. Albright, who ran the company for more than forty years, many of them spent in court defending his product.

The Morse Signal Key is shown in fig. 10.* It consists of a brass lever, A, four or five inches in length, which is hung upon a steel arbor, G, between adjustable set screws, D D, in such a manner as to allow it to move freely in a vertical direction. This movement, however, is limited in one direction by the anvil C, and in the other by the adjustable set-screw, F.

Question/ Purpose:

Why are there so many different telegraph keys? What are the differences? What do they do? Can we just use any key as a telegraph key? what caused developing so many different designs? The purpose of this project is to investigate and make a close observation of different telegraph keys and build a simple working model of a telegraph key.

Identify Variables:

Variables that may affect the working quality, comfort and performance of a telegraph key are as follows:

    1. Pressure needed to push the key.
    2. Swing or gap (the distance that key is pushed until contact is made)
    3. Contact type (I added this variable later when I noticed that regular Iron as contact will quickly oxidize and stops working. Also in one test contacts stuck to each other by spark)


My hypothesis is that the swing period and key pressure must be adjustable so the operator can adjust it based on his muscle strength and the weight of hand.

Contacts must be made from metals that do not get oxidized or different metals that do not get welded to each other.

Experiment Design:

In order to do any experiments related to function, quality and comfort of a telegraph key, we will first build a sample telegraph key. Then we can adjust or modify one component at a time and do the test.


Use a piece of wood about 5″ x 7″ as a base for your telegraph key. You will need an arm for the key. A metal arm such as an aluminum or brass square rod is a good choice, but you can also use wood for your model.

In this model we used a wood dowel for the arm and we used two other pieces of wood dowel for the arm stand. They are all drilled so we can use a nail to connect them to each other. Arm is able to swing like a see-saw.

For upper contact we used a zinc plated screw. We then used a wire to connect this screw to another screw at the back of the switch, from where will be connected to the circuit wires. If the arm, connectors and the base were metal, we did not have to use such a wire. Metal is conductive and does transfer the electricity to the screw on the base.

To make sure that the key will remain open while it is not being pressed, we have used a robber band at the tail of the arm. Rubber band will pull the tail of the arm down, so the contact side goes up.

Now we need a stopper to make sure that the robber band does not pull the tail all the way down. We placed a screw under the tail to stop it from going down.

For the bottom contact we used a steel screw! copper or graphite could be better choices, but we couldn’t find those in our junk box.

Bottom contact can be connected to the second contact screw at the back of the key board by a wire, copper strip or aluminum strip that we used in our model.

For the handle we could use a knob, but we made it from another wood dowel.

When the key was ready, we adjusted the stopper screw, so the contact gap was about 2 millimeter and working with key was quite comfortable.

Another working model:

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.

A simple key and sounder system:

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.

    • 2 Pieces of wood. (Any kind of wood will do fine.)
    • 9 Small wood screws or nails.
    • 2 Large IRON nails. (About 2-3 inches long.)
    • 4 Flat strips of metal. Three of them should be about 4 inches long.
      One should be about 7 inches long and MUST be iron-bearing or “ferrous” metal which is metal that is attracted by a magnet.
      (This kind of metal is often found in food cans.)
    • 20 ft or more of INSULATED solid wire.
      (22 – 30 gauge…. about 1/64 inch or less in diameter.)
    • 2 Flashlight batteries.

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 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.

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 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.

This model was made by 13 year-old Claire Berry in KwaZulu-Natal, South Africa.

It won a high grade in a science project.

Materials and Equipment:


Results of Experiment (Observation):

After you make your working model of a telegraph key, you can test it by placing it in a simple circuit with a sounder, a buzzer or a miniature light bulb. How does it work? What problems did you observe at you initial tries? What did you do to improve your design or solve the problems? What are the final specification of your key?


You may need some calculation while preparing your design. If you do aany calculation, write them at this section.

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List your references.