Flick-o-wrist sensor

[Brightlightredlight]

Hello, can anyone really explain a lazy flick of the wrist sensor in P4's ? Is it actually a tiny mercury switch or what really activates the module to come on. Has anyone ever replaced the switch ? If this was such a great feature why did Pulsar not continue this with their later watches ? Any real cure for a lazy flick of the wrist action ? Thanks.

[767Geoff]

From enquiring minds, I too want to know. I have a pulsar 902 that lights up when sitting flat on a table and someone walks by.

Needs to be toned down or bypassed so that it does not work and only the button works.

Cheers

[SASM]

The problem with these switches is that they are active low (permanently closed and only open when activated). The contacts of the switch were not made for 40 years or more of operation as the material they used corrodes (you can see that if the contacts look blackish instead of silver grey inside the glass tube). New switches are available in China, but I am not allowed to import them to the EU. That´s one of the reasons why I used a completely different kind of switch in the #HGWC watches.

[bruce wegmann]

To actually answer the question...yes, they are grain-of-rice-sized glass tubes (distantly related to the "Tilt" switch in pinball machines). A bead of mercury approximately 1 cubic millimeter in volume provides the inertial component. In operation, the mercury bead is forced off the "wettable" electrode pin (the other pin is a steel alloy which mercury does not adhere to), momentarily opening the switch (which is normally closed). Reversing the flick drops the bead back onto the wettable pin and re-closes the switch. If the switch opens and closes in 125 to 165 milliseconds (1/8 to 1/6 second), the circuit recognizes it as a valid command, and displays the time. "Open" durations outside this range are ignored (for you engineers, this is called "time-domain sensitivity"). It was simply an energy-saving feature, designed to keep random arm and hand motions from accidentally activating the display function and prematurely draining the batteries.
Auto-Command modules are found in all P4 models, Special Edition Touch-Command Dress, and 902 and 903 Calculators (a few Sport watches have also been found to have AC modules...probably an oversight at the factory when the watch was serviced, as no 3502s were originally issued that way; the AC switch is half the size used on other modules, and could be easily overlooked).
This would have worked a lot better if there had been some provision for switching the Auto-Command function on and off (an oversight which was corrected on the Gillette Touch-Sensor modules.

[767Geoff]

Thanks Bruce and SASM

my 902 flick lights up at the slightest vibration. Actually draining the batteries, while on display in its case, as someone walks by. So where is the switch so that I can remove it? Am I correct in assuming this will disable the flick response but still allow the buttons to activate the display.

Or, does anyone have a Mercury switch that works!

Geoff