The PropKeyer - A Multi-mode Morse Keyer

PropKeyer photo

A Little Background

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".

The PropKeyer

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.

PropKeyerSys photo

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.

Modes of Operation

The modes of operation emulated by the PropKeyer are:

Inside the Hardware and Software

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
Detailed documentation PropKeyer_exp_docs.pdf 101
Construction and Usage Notes PK_Const_and_Use_Notes.pdf 19

Possible Future Developments

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.

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