The (O)ptions menu, (T)one submenu provides the signaling generator option
G that uses screen blinking to send the Morse code. This form of signaling
is used by the U.S. Navy for signaling between ships when other forms of
communications is not available. This option has been added to Morse
Academy because of several requests from hearing impaired persons who wish
to learn the code.
There are many problems in using the PC screen to signal CW. To reduce the
visual noise appearing on the screen care has to be taken to change the
screen contents during times when the electron beam is not updating the
screen image. The Morse Academy driver has been written to perform the
screen update in the minimum number of CPU cycles possible while the beam
is returning from the bottom to the top (HRI time). This restricts the
maximum signaling rate to the screen refresh rate. For a 60 Hz non-
interlaced screen, refresh occurs approximately every 16 milliseconds.
At 10 WPM, where the sending time for a dot is 120 milliseconds, this means
that an error of 15% can occur for one element. As the speed increases the
error does also. High resolution non-interlaced monitors will perform better
than interlaced types. LCD's used in laptop or notebook computers are very
slow and are not suitable for visual signaling.
The eye can not easily handle signaling rates as fast as those as the ear.
This fact combined with the larger error due to 16 ms timing increments make
copying visual signaling difficult at high speeds.
More accurate visual signaling is possible using external hardware the PC's
internal sound generator, e.g. Morse Academy's external tone generator, or
the parallel or RS232 port's. (See appendix C and E for more information on
methods of signaling).
Morse Academy was written to use the screen as a display of information
while the student listened to the audio practice. Adapting it to display
the same information and use the screen for signaling involved considerable
modification. Hopefully any errors introduced as a result are minor. Still
some sessions proved too difficult to modify and had to be dropped when
using visual signaling, e.g. the (E)ndurance session. Depending on the
response to this new mode of training, future developments may extend visual
signaling to support all Morse Academy functionality.
User comments on the visual signaling option would be appreciated.
By Joe Speroni
Email: