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OT with a link but still LED and timing display involved...

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767Geoff

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OT with a link but still LED and timing display involved...

Post06 Feb 2008, 09:02

Just posted at the HP museum my HP calc restorations.

One of the restorations involved an HP 45 with an 'easter egg' in the form of a timing display. It seems the HP 45 came out before HP had access to Quartz crystals for time control.

The engineers decided to program a rom sequence and include the complimentary wiring for testing for a proposed timer in the next version called the HP 55. The sequence and programming resulted in a non-documented timing sequence that had all the correct display of an LED stop watch but on average a loss of 7 seconds per minute. Remember they were not producing the HP 45 with an accurate circuit but just for practice as it were. The access to the time display was extremely awkward as it was not supposed to be accessable by the general user. It required one to press the RCL key, then simultaneously press the CHS+7+8 keys.

Well it turns out that a simple inclusion of a 780 kHz crystal in series with a choke removed is all that is required to turn the 7 second loss per minute into a quartz accuracy.

Well I did it! After restoring the calc and securing a 780 kHz crystal my HP 45 is now as accurate as my best LED wristwatch. The access to the display has also been simplified, now all I have to do is press the RCL key and then press the enter key and voila!

If you are interested I have a few links below (the last link has HP 01 content so not entirely off topic!)

Here is the HP45 during restoration:
http://www.hpmuseum.org/cgi-sys/cgiwrap ... 014#131014

Here is the original article on the HP 45 quartz conversion:
http://www.hpmuseum.org/45crys.htm

and here are the pictures of the collection:
http://www.hpmuseum.org/cgi-sys/cgiwrap ... 145#132145

here is a shot of the display when the RCL and modified ENTER key are pushed 00 hours: 09 minutes: 18 seconds: 18 hundreds of a second.(hours.minutes_seconds______hundreds).
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rewolf

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: OT with a link but still LED and timing display involved..

Post06 Feb 2008, 10:54

Very nice LED watch :-D
So you finally managed to get that odd frequency quartz crystal - where did you find it?
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767Geoff

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: OT with a link but still LED and timing display involved..

Post06 Feb 2008, 14:22

Ebay had a HP 55 used keyboard and battery holder assembly with perfect battery tabs that I needed for the HP 55 restoration. That keyboard is similar to the HP 45 and also contained the 784kHz crystal.

I harvested the battery holder for the HP 55 and the crystal for the HP 45. I could not find that frequency crystal any other way!

Cheers, Geoff
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: OT with a link but still LED and timing display involved..

Post06 Feb 2008, 19:18

Nice collection there Geoff, They seem to be quite popular is there something special about HP calculators that you like I've got quite a few LED calc's but never really gave HP a thought.
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767Geoff

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: OT with a link but still LED and timing display involved..

Post06 Feb 2008, 19:58

I would say that HP is to the calculator world as Synchronar and Pulsar are to the LED watch world and Omega and Rolex are to the mechanical watch world.

They beat Texas to the goal post with their calculators by a few years. Although there were other LED calcs around and some were even good none had the construction or functions tha HP incorporated.

The circuit boards are all removable and inserted on pin stands. All connectors are gold plated. The calc was easily dis-assemble and the quality of case, finish, led and electronics were miles above the competition (BOWMAR, SUMMIT, LITRONIX etc)

They produced the first esoteric function calculator HP 35 which truly replaced the slide rule. Up till then the calcs only multiplied and divided. All their calcs had 9.99999999 e99 displays with display options from the start. No one else...

I could go on but to a collector here is a perspective:
    first Reverse Polish Notation calc (more efficient use of key and inputs than algebriac)
    first esoteric function calc
    first multi display function; SCI, ENG, FIX
    first programmable
    first retained memory programmable
    HP 65 used in the latter Apollo program
    HP 41cx special order with timer installed in early Shuttles
    HP 41cx standard issue to all 3 pilots on shuttle


Lots of firsts here. Also for comparison I have a NOS HP 67 with the works mentioned in my collection article and valued around $1000.00 USD.

I also have TI's first programmable card reader calc with the works valued around $100.00.

Got to take the dog out and go to work, back later!

Cheers, Geoff

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