DB-8 First Update

This update (2/8/2009) shows the bug in a further state of finishing, ready for on-the-air testing.  It illustrates the assembly and wiring of the instrument.  As before, these are high-resolution pictures - left-clicking on any one of them will enlarge it for closer inspection.


      The bug was disassembled for further finishing.  The base was given a milled finish on its top, and a concave chamfer was milled into the top edges.


     An important feature of the bug was a mechanism to make fine adjustments of the duty cycle of the dots and dashes.  The most direct way to do this is with a spring-loaded screw-thread mechanism.  As shown below, this involved two "sliders", one for the dots and one for the dashes, that would carry the magnetic reed switches.


     The two sliders run in a channel milled into the base of the bug.  Movement is controlled by a 4-40 screw that extended in from the side - a coil spring that fits into a pocket on the slider provides a return force.

    The amount of movement available is shown at the lower left.  It allows the magnet-switch tube to move back and forth by about 5/16 inch.  This has proven sufficient for the amount of adjustment required.  Shown at the lower right is the combination front foot / slider retainer mounted in place.  Two nylon setscrews can be adjusted to remove any play in the system.  The machined surfaces are smooth enough so that lubrication is not needed.  

     The view below shows the switch tubes projecting up through the base.  The solid uprights are the rest stops for the pendulums.  The panel at the right shows the electrical connection terminal posts mounted to the base.  My usual practice is to locate the "hot" post away from the (right-handed) operator for safety reasons that are now not very relevant.

     The other end of the bug holds the driving lever and the dot and dash pendulums.  The top panel below shows the bearings of the driving lever and the two driver magnets (with the red and black knobs) at its end.  They will exert an attracting force on the pendulum magnets.

     The two lower panels show the details of the pendulum.  Each pendulum magnet is borne in a holder with a slot for adjustment which will allow for proper positioning of the magnet under the driving lever magnet.  The pendulum tube is inside threaded at its far end, and a pair of axial setscrews is used to hold the signal magnet (for activating the reed switch) at a position that is the proper distance away from the switch.

 Above, Upper Left - This is the base, with the base of the pendulum and lever assembly mounted on it.  Upper Right - Shows the driving lever in place (it actually has to wait until the pendulums (Lower Left) are installed.  Lower Right - All moving components are installed.  

     The unit is ready for the top plate, which will hold the upper bearings of the lever and pendulum and secure the contact pillars.  The threaded rods extending from the contact pillars are used to keep the washers in place as the top (Right) is lowered into place.  Shown below is a view of the bottom of the base and the underside of the lever and pendulum assembly.  It can be removed from the base as a functional unit.

     The last part of the assembly is the wiring.  The copper strip (Below, Upper Left) is a piece of printed circuit material that has been divided into three lands for the wiring connections.  At the Lower Left is the wiring coming from the reed switches (red, white, and black wires).  The two black wires form a common junction and are connected to the "hot" binding post via the yellow wire.  The free ends of the switch leads (red and white) are connected in series with the lever contacts at the rear of the key (Upper Right).   

This arrangement requires that the lever contacts be closed before a closure of the reed switches can be detected.  This "wired AND" circuit prevents false signals due to bouncing of the pendulums.  The overall wiring is shown at the Lower Right.

Final Touches -

The most frequently used adjustments are fitted with knurled knobs, but several adjustments require Allen wrenches.  Since I can never keep track of them, there are two that can be stored in the base of the key (there are two sizes of screws to adjust).

      So here it is so far.  Initial tests by ear have produced acceptable CW without a steep learning curve.  Even though the final test will be how it sounds to others, there are some timing measurements to be made that will help with the fine tuning of the design.