A brief look back in(side) time.

[popoki nui]

I'm not really sure in which forum this belongs best, so I'll just try here.

I needed to perform a small corrective procedure on one of my Pulsar Time Computer LED watches. I was delaying that until it was time to change batteries, which I did today, and I thought it might be of interest to some (some/few/none etc) of you to come with me for a look inside what was the world's first solid-state timepiece.
Attachment 18735
My P4-series "Big Time" from 1975. In order to not have to push a button to see the time, Pulsar included the "Auto Command" system; a tiny glass mercury rocker switch which activated the LED display with a flick of the wrist. Great in theory, but few worked correctly. Often they were either too sensitive, or not sensitive enough. Mine was much too sensitive, which caused excessinve battery drain. So the procedure today was to disconnect the mercury switch while I was replacing the batteries.
Attachment 18736

The case back is a two-piece affair: a stamped stainless steel back with battery contacts, attached to the case by a threaded locking ring:
Attachment 18737
A little tricky to thread properly and not cross-thread, but the system has the advantage of not twisting/distorting the O-ring on the case as can happed with one-piece threaded case backs. Help to keep Pulsar water resistant.

The back of the module:
Attachment 18738
Attachment 18739
The module is held in place by two tiny screws. Under the 403 identification sticker is the quartz crystal, which zips along at the common 32,768Hz. To adjust the timing to the 60 seconds/year it is capable of, Pulsar repair centres had their own timing machine, and adjustments were made via the square~ish shaped trimmer and a special tool.

Front of the module:
Attachment 18740
Time Computer modules were unique: they used glass tubes containing magnetic reed switches on the module, and command buttons containing tiny, very powerful rare-earth magnets and a curved leaf spring. When the button is pressed, the tiny magnet inside moves closer to reed switches (upper and lower in the photo) immediately adjacent to each button; the reeds connect and sends the time or date signal to the LED display. Earlier models used the same system to set the time and date, too. Trippy, eh? As complicated as this sounds, the advantage is that the button(s) are completely sealed from the inside, via a metal plate soldered in place. So nothing penetrates the case, including water.

Attachment 18746
Attachment 18744

Other cool features were completely epoxy-sealed LED's and silicone-sealed microchip (so if water ever did get inside, the important bits weren't damaged), and an ambient light sensor which brightened and dimmed the LED display based on the brightness of the immediate environment. That helped save battery power.
Pulsar red "time screen" crystals were either red tempered glass, or synthetic sapphire with a red laminated filter (yes, we had sapphire crystals way back then!), and were bonded to the case with aerospace-grade epoxy. That, and the sealed command buttons and case back O-ring meant Pulsar could easily withstand useable depths of up to 100ft. So you needn't gasp in horror when you see my Pulsars in the water!

My little disconnection procedure involved simply cutting the "L" shaped flat wire at the base of the Auto Command switch in the module photo above. Then it was just a matter of checking/lubricating the back O-ring, installing fresh high-drain cells, and reinstalling the case back.

Done!
Attachment 18747

Those of you still awake...thanks for reading!

~Sherry.

[popoki nui]

Very interesting, Sherry.

I was too young - and the watches too expensive back then - when these "novelties" arrived to the market. I never had a chance to get one. As you know (much better than me) they started to be replaced for the more usual LCDs so, somehow, they did not make part of my interest in watches. Glad you had the generosity to post this information here. Thank you, Sherry.

The early LED-LCD story is interesting. Seiko hit quartz market first with Astron, but Hamilton Pulsar was the first completely solid-state wristwatch. Seiko never made LED watches; I think they saw the shortcomings of the LED display (poor battery life, two-handed operation, poor visibility in bright daylight), and went the LCD route. But despitetheir technological prowess, Seiko's LCD lagged behind Pulsar's LED throughout most of the 1970's in terms of function. By 1975, Seiko had barely introduced a digital watch with a date (and one with a basic chronograph), and their watches had no shock or water resistance. Pulsar watches, comparatively, had month, date, AM/PM, and they had the world's first calculator watch, which even included a memory. And the non-calc Pulsars were functionally water resistant to 100ft, and shock resistant to 2500 G.
Yet those obvious shortcomings of the LED display vs the LCD couldn't be ignored for long, and by the late 70's, the LED's short run was over.
(FYI: LED= Light Emitting Diode. LCD= Liquid Crystal Display.)

~Sherry.