PicoBug I

 The NanoBug IV (a.k.a PicoBug I) Is now the Smallest in the Series.

     Previous attempts to build a very small bug arrived at a design that used a vertical and statically-balanced pendulum in a right-angle arrangement.  The last of these, the NanoBug III, was quite small.  However, experience in building it indicated that there were some places in which dimensions could be further trimmed without compromising the functionality.  So another instrument was planned and constructed.  It turned out to be significantly smaller than the other bugs in this series, so instead of calling it NanoBug IV, it became PicoBug I.  It has proven to be stable and reliable in on-the-air tests.


Changes from the Previous Version

            While the basic vertical pendulum and right angle design were retained, the overall length (in the direction of the pendulum axis) was reduced by shrinking the block on which the contact posts and bearing supported were mounted.  Further reduction was achieved by moving the speed adjustment magnet to the pendulum and placing the driver magnet on the end of the lever assembly.  The dash contact pillar was made to do double duty as a connection terminal, and some extra width was trimmed away.  The top plate was removed to make room for the speed-adjust screw and to allow placement of the connection terminals.  Essential parts of the new bug are shown below.

With the exception of the locations of the speed-adjust screw and the switch tube lock, the adjustments and principle of operation are the same as in the previous NanoBug.  The dot-adjust screw adjusts both the paddle travel and the weight of the dot string (by determining how far the pendulum is displaced during its oscillations).  The whole practical range of dot weights is covered with little noticeable difference in the distance of paddle travel.  There is some interaction between the dot-weight and the speed setting because of small changes in the starting position of the pendulum at different magnetic field strengths.  To save space within the mounting block, screw connection terminals were used instead of the phone jack of the previous version.


Construction of the PicoBug

The bug consists of three basic units that are mounted on a base plate.  They are

the base block, the lever assembly, and the pendulum.  Parts for the first two

of these units are shown below.

The base block (right, 329) will hold the contact pillars, the connection terminals, and the support for the pendulum.  The reed-switch tube (not shown) will fit in a hole drilled through the block and the pendulum support, which is held in place by two screws.  The lever assembly (left, 344) pivots on the two brass balls shown, which are fastened onto the lever plate and will fit precisely into the pendulum support holes.  A lateral extension of the lever plate (brass rod) will hold the magnet arm, and the fingerpieces attach to the end of the plate.  The dot contact is a polished brass screw, while the dash contact is a brass extension of the lever plate.  (The small numbers are for my identification of the photos.)

            The next set of pictures shows the sequence of assembly of the base block and its parts.  In the upper left (346) are the base plate of the key, and the parts that will be mounted on it.  At the upper center (349), the base block is mounted, and at the upper right (351) the pendulum support is attached.  The ground connection post and the rest stop are added at the lower left (355), and the contact pillars (lower center, 362) are next added.  The shaft for the pendulum, with the lever plate tension spring appears at the lower right (363).

       The lever arm assembly is next.  The parts are at the upper left (344), and most of the assembly is shown in the upper right (317).  At the lower left (315) is the complete lever assembly.


Its location in the assembled key is at the lower right (304).  In operation, the spring presses the lever plate float against the lever support, and pressing either fingerpiece “rocks” the plate out of position.  The two brass balls maintain the lever in register; they run in polished holes in the support upright that are 0.001 inches oversize. 

      Prior to final finishing and polishing, the key was assembled for a preliminary test.  At the upper left (314), the lever is mounted to the base block; the pendulum and its associated parts are at the upper left (309).  In (306) the pendulum is in place and the key is waiting for the lever magnet arm

to be attached.  The final rough assembly is at the bottom right (302).

        At this stage the key was functional and ready for a quick test, which is shown below.  The reed switch was temporarily placed in the switch tube, and clip leads made the connections to the test oscillator.  The key worked well, and the proper position of the reed switch within the tube was marked.  At this point the key was disassembled for final machining and polishing.

Final Assembly

            The three modules are at the upper left (427), and are assembled as shown (without the pendulum) at the upper right (412).  The wiring between the contacts and the reed switch runs in channels cut in the base (lower left, 435), with ample slack allowed for adjustment of the reed switch position.  The finished key is at the lower right (380).

 Some Final Comments

            Several views of the finished key are shown here.  While the key is quite small, its weight of 9.7 ounces and the rubber feet make it surprisingly stable in use, and it does not need to be held down to keep it in  place.  The speed range is range is from about 10 to 25 words per minute,



with minimal interaction between settings, although some “touching up” at each speed setting made for better sounding CW.  Because of the statically-balanced pendulum, the bug is very insensitive to position – it can operate on its side or upside-down.  While mobile-in-motion CW is a possibility and a temptation, safety considerations argue against this application.

            So how does this bug compare with its predecessors?  The picture above shows it in comparison with the NanoBug III – it is definitely smaller.  The size of the bug, in this configuration at least, seems to have reached a lower limit for a bug that can be used reliably with one hand.  The feel of the bug is like that of Nano III.  In contrast to NanoBug II, it has a well-defined center position; the ball pivots give it a very smooth action.  Paddle travel in the dot direction is comfortably small, unlike Nano I, which required rather large paddle travel and was very sensitive to the position of the bug.  Pico I uses polished aluminum fingerpieces that have minimal drag on the fingers, feeling more like polished wood than the acrylic plastic used on the other bugs.

Eliminating some of the parts of the NanoBug III has resulted in a smaller and lighter instrument with essentially the same feel and performance.  I suppose that this is consistent with the goals of QRP operation.

            There is still room for improvement; the current method for setting the position of the magnet arm makes it subject to being bumped out of position, and this will be remedied in the next try.   A couple of new designs, of roughly the same size but with different arrangements of parts, are in progress, and it remains to be seen if they will be a significant improvement.







73 de Rich, WB9LPU