While itís possible to send and receive with MorseKOB using just the keyboard and speakers, sooner or later youíll probably want to hook up a key and maybe a sounder. There are three options to choose from:
Each of these interface options connects to the computer via an RS232 serial port. Since few computers come with a serial port nowadays, most likely youíll need a USB adapter cable to make the necessary connection. See the USB-to-serial adapters section for some recommendations.
|Warning: Switching the current on and off in a circuit containing
inductive components like the coils of a sounder or relay can generate
high voltage transients which are likely to interfere with and possibly
damage sensitive electronic devices. Itís important to guard against
this by placing a ďsnubberĒ across all sounder or relay terminals. See
the Snubbers section for more information.
Static electricity is another source of high voltage that can damage electronic components, for example if you touch the metal part of your key while your body is charged with static electricity. Although unlikely, it has happened, so take appropriate precautions. Using a USB-to-serial adapter cable instead of connecting directly to the computerís serial port can limit the extent of possible damage.
The easiest way to connect a key is to take a serial cable with a female DB9 connector on one end and simply cut off the connector at the other end. You can buy a Belkin F2N209-06 serial extension cable for $5 or less from many online suppliers.
Youíll need to find which wires correspond to pins 4 and 6 on the connector, and connect those two wires to your key. Unfortunately, thereís no standard color code for serial cables. For the Belkin F2N209-06 cable the correct wires are orange and green, but if you have a different cable then youíll need to use an ohmmeter or continuity tester to determine the right wires.
|RS Catalog #|
|TIP120 NPN Darlington transistor||276-2068|
|10 Kohm 1/4 watt resistor||271-1335|
|1N4005 micro 1 amp diode||276-1104|
|9-pin D-sub female connector||276-1538|
|D-sub connector hood||276-1539|
In order to drive an external sounder from the serial port, youíll need an interface circuit like the one shown above. The circuit can be built from parts available at Radio Shack for about $6. The components can even be made to fit inside a DB9 serial port connector, although you may prefer to build it in a project box.
The loop interface circuit allows the computer to function as part of a normal telegraph loop. In its simplest configuration, that telegraph loop would consist of a key, sounder, and power supply, but it could contain other instruments as well. A circuit diagram and explanation of its operation can be found in the MorseKOB Loop Interface document.
Circuit boards for the loop interface are available from the Morse Telegraph Club. Youíll have to buy the circuit components yourself, mount and solder the components on the board, and provide your own enclosure. Write to firstname.lastname@example.org for information on availability and cost of the circuit boards.
Most likely youíll be using a USB adapter cable to provide the necessary serial port for your interface. Itís important to understand that MorseKOB uses the RS232 control lines of the serial interface, not the data lines. This means that an adapter that may perform very well in a more conventional application could be unsuitable for MorseKOB. To play it safe, use one of the following adapters that are known to work. And remember, you may have to install driver software that comes with your particular adapter.
When a key in a telegraph loop is opened, the collapsing magnetic field in the inductors in the circuit (sounder and relay coils) caused by the sudden cessation of current flow creates a large transient voltage across the key contacts. A snubber, also known as a spark suppressor or spark killer, is a device used to damp this transient spike. In traditional telegraph circuits, the snubber was used to prevent pitting of the key contacts. With MorseKOB, however, the more important reason for using a snubber is to prevent interference or possible damage to sensitive components in the computer or USB-to-serial adapter.
The best place to put the snubber is directly across the terminals of every sounder or relay in the circuit, as this minimizes the amount of radiated electromagnetic interference. If thatís not practical, then snubbers should be placed across all keys in the circuit. (Note: a snubber is not required for the ďkey onlyĒ interface. Itís only an issue when a sounder or relay is in the circuit.)
The following snubber designs have all been used successfully:
The following table identifies the RS232 lines used by the program to interface with an external key or sounder.
|Manual key or
|Manual key or
*The color code shown is for the Belkin model F2N209-06 serial extension cable. Some other cables follow the same color code, some do not.