Ball size: 113/32" (35.8mm)
Designed for EU-M30 endoscopic ultrasound system, but in fact it's pretty much standard raw output 3-button pointing device.
Actual trackball unit is Tamagawa TA3414N, mounted in rectangular steel case with buttons. Quality of trackball itself is very high: classic scheme with two shafts and 5th. support bearing is used.
Main bearings are of 3x7x3mm size, and support one is 4x9x4mm. They're unmarked, but dimensions correspond to the MR683 and MR684 in NSK catalogue. Both are of top grade, and despite their quarter-century age didn't even required lubrication change - rotation is perfect: without ball, shafts are spinning by own inertia for about half minute upon flick. Interesting detail is a separate ring, freely laying between the ball and upper cover: probably intended to wipe ball surface, protecting internals from contamination. It does not give any remarkable resistance to ball rotation, but produces annoying wobbling - so I've hot-glued it to the cover.
Signals from 18-slot discs are read by photointerrupters marked S6Z and purified by Toshiba TC74ACT14 Schmitt inverter IC. Resolution is 216 PPR (49 CPI).
Switches are ordinary 6mm tact buttons, covered with soft plastic membrane with square inserts. Actuation force is a bit high, and button's surface is level to the case - so, clicking is not as convenient as in more common microswitch-based design, but totally usable.
Proprietary 10-pin connector looks similar to MiniDIN used on PS/2 or bus mice, but have precision casting shell with complicated profile, and contacts arranged in 4 rows at fixed pitch.
Conversion to USB was simple: I've added ELAN Microelectronics EM84502AP controller with PS/2-USB adapter, soldered directly to the connector wires, and replaced the cable, keeping its original color.
Tracking feels amazingly smooth, and device is really pleasant to use. Of course, "old-school" arrangement of buttons above the ball is not optimal today, so I've briefly tried to use it upside down with axis signals inverted - but finally returned to correct orientation and assigned click-lock function to the middle button. Also, two-hand operation with trackball as pointing-only device in conjunction with external buttons (belonging to the notebook's touchpad) turned out to be surprisingly convenient. Traditionally, device was used to prepare this article.
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