Most of us are familiar with the old-fashioned "straight" telegrapher's key. We've seen them pictured in photographs and movies for years, usually to great dramatic effect. This is the type of key with a single lever, having a knob on the front which the operator grasped in his or her fingers. Dots and dashes of Morse code were formed by vertical motion of the sender's wrist and forearm, which opened and closed a set of electrical contacts on the key, turning a radio transmitter off and on or sending bursts of current down a wire.
Today, the hands-down favorite among radio amateurs for sending code is a quite different device. Known as the "iambic" key, it's a horizontally-acting dual-paddle key, similar to two straight keys mounted back-to-back and turned on their side. There are two separate sets of electrical contacts, one of which is closed by pressing the left paddle, the other by pressing the right one. In contrast to the older, strictly mechanical keys, the iambic key is meant to be used with an electronic keyer, which translates the contact closures into strings of dots and dashes to be sent to the radio transmitter.
Along the way from the time of the straight key to the invention of the iambic key, several different types of mechanical keys came into (and fell out of) use, all with the goal of faster and more accurate code. It also became quickly evident that a side-to-side motion was easier on the operator than the up-and-down, brass-pounding motion of the earlier straight key. Many early telegraph operators developed permanent neuromuscular damage due to carpal tunnel syndrome, known in those days as "telegrapher's paralysis" or "glass arm".
This project is a multi-mode electronic keyer which emulates a variety of these older types of keys, enabling the owner of a modern iambic dual-paddle key to experience the feel of differing Morse code sending techniques that have developed over the last 150 years of the telegrapher's art. In addition, the PropKeyer supports the use of a conventional straight key, as well as a full PS/2 computer keyboard, so that code characters can be sent simply by typing them.
As you can see in the photographs, the PropKeyer controls are quite simple: A five-position switch selects the various modes of operation, and the code speed can be varied over a range of 5 to 40 words per minute by a rotary potentiometer in the center of the front panel. An LED, labeled "CW" blinks on and off with the code being sent, as a visual indication. On the side of the cabinet is a small loudspeaker and volume control which reproduces the code as an 800 Hertz tone for audible monitoring.
The modes of operation emulated by the PropKeyer are:
Iambic A - A series of dots or dashes is transmitted when the operator presses the left or right paddle, respectively. (This is the usual setup for a right-handed person. Some left-handers find it convenient to reverse the function of the paddles.) If both paddles are pressed simultaneously, alternating dots and dashes are sent.
Iambic B - This mode is nearly identical with iambic A, with one subtle difference: At the end of the alternating dot-dash series that occurs when both paddles are pressed, an extra code element is sent which is the opposite of the element that was in progress when the paddles were released. In other words, if a dot was in progress when both paddles are released, a dash is sent, and vice-versa.
Bug - also referred to as a semi-automatic or "Vibroplex" key, after the company that originally manufactured and patented this design around 1904 (and, incidentally, is still manufacturing them today). The bug key has, in effect, a single set of electrical contacts and features a horizontal arm, or pendulum, which transmits a series of dots when the paddle is pushed to the right and held. The dot rate is controlled by a sliding weight on the vibrating arm. When the arm is pushed to the left, the contacts are simply closed and the operator forms the individual dashes by finger action. An arrangement of springs keeps the arm centered when no code is being sent. True bug keys are strictly mechanical and, unlike the iambic keys, do not require an electronic keyer to function. The bug appeared at a fairly early stage in the development of telegraphy and was widely adopted when it became evident that a side-to-side motion resulted in faster sending and less operator fatigue.
Sideswiper - The sideswiper (also known as a "sidewinder", or "cootie" key) was another early departure from the vertical acting straight key. This key is mechanically simpler and so less expensive than the Vibroplex bug. It has a single paddle which can be moved to either side and simply closes a set of contacts, regardless of which direction the paddle is moved. The length of both dots and dashes is under control of the operator who simply slaps the paddle back and forth.
Console - The PropKeyer accepts a PS/2 computer keyboard. When this mode is selected characters are fully formed and transmitted by typing on the keyboard. The internal buffer only holds 16 characters, so a fast typist should be careful not to get too far ahead of the output stream. The dash-to-dot ratio, or "dash weight" is controlled by software running within the PropKeyer. Standard dash weight is 3:1, but this can be changed by the operator over a range from 2:1 to 6:1 by typing Control-w on the keyboard, followed by a single digit number between 2 and 6.
Inter-character spacing is also under software control and is normally set equal to seven dot periods. This can be changed in increments of 3 dot periods by typing Control-f and a single digit number from 0 to 9. This is known as "Farnsworth" spacing and is often used to increase intelligibility when slow code speeds are being used. Beginning code trainees who are trying to increase their copying ability may also find this spacing beneficial. With longer spaces between characters, individual characters can be sent at high speed, while the overall words-per-minute rate remains low.
The following table contains links to a number of documents detailing the hardware and software that make up the PropKeyer. Enough information is contained here to enable anyone to reproduce this equipment.
Left-click on any .PDF file name to view it on-line, or you can right-click, then save the link to your computer. You will need Adobe Acrobat reader to view these files. Click here if you need to download the latest version of this free software from the Adobe web site.
The source code is presented as a zipped-up suite of programs in Parallax's SPIN language, which together make up the complete software package for the PropKeyer. After these programs are downloaded to your computer and un-zipped, they are ready to be programmed directly into the Propeller chip.
|Description||File Name||Size, kB|
|Hardware Block Diagram||PropKeyer_HW_block_diagram.pdf||58|
|Electrical Schematic Diagram||PropKeyer_sch.pdf||42|
|Bill of Materials||PropKeyer_BOM.pdf||16|
|Software Flow Chart||PropKeyer_SW_flow_chart.pdf||17|
|Propeller Source Code||PropKeyer_SW.zip||27|
|Construction and Usage Notes||PK_Const_and_Use_Notes.pdf||19|
The EEPROM supplied on the Propeller Development Board has a large area of unused space -- 32k bytes -- so it's entirely feasible to store several strings of characters which can be transmitted at the push of a button.Also, the sound of the sidetone audio monitor could be greatly improved. Right now, a simple square wave drives the small loudspeaker resulting in a rather raucous sound. A close approximation of a sine wave could be generated in software and passed on to the speaker through a linear amplifier.
Another helpful addition would be a diagnostic program which would be enabled by a jumper on the circuit board. This would write a few selected variables out the USB port for display on a computer running a terminal program such as Microsoft's HyperTerminal or Parallax Serial Terminal.
There's plenty of room in program memory and in the non-volatile EEPROM for all of these additions. However, improving the sound would probably mean including one more integrated circuit in the design, making it a more complex project. At any rate, some future version of the PropKeyer may well include these changes, as well as any others that come to mind.