Geodat, any info about the ic's and unit?


Hi there,

This was sent to me for battery replacement. Two nicads which are toast.

It contains an HPIL module (at least it looks like one). When the unit is assembled and the HPIL is plugged into the HP 41C and simutaneously into the Geodat pca the following module titles are found in CAT 2:

printer 2e
mass st 1h
ctl fns

With the HPIL plugged into the HP 41C and not attached to the Geodat pca via the 16 pin plug nothing displays, in fact the calculator freezes.

I am assuming that the ROM modules reside in the EPROM (chip with the white paper label).

It will be an easy procedure to replace the batteries but I was wondering if anyone had any more info for this that I could supply the owner with and maybe include in the book.

check out the following pictures:

Top shell

Top shell removed showing Geodat PCA and EPROM with white paper label:

HPIL link and battery; two views:

Cheers, Geoff


Hi Geoff,
I have the Geodat unit and a HP-41C module called "Geodat 126C". It is a takeover module that redefines nearly all the keys when the calculator boots. It only works with my HP-41CV, the HP-41CX gets a "memory lost" when this module is inserted into it.

Since the backside of the unit includes some reference to functions, I have assumed that the user can enter some user-defined functions which the Geodat then uses for calculations.

Btw, my Geodat unit has the "Printer enable" switch of the HP-IL module set to "disable".

Could it be that the calc freezes because the HP-IL loop is broken?

Kind regards, Klaus

Edited: 15 Mar 2010, 4:13 a.m.



I am a Surveyor and just from memory I can recall that the Geodat was a data collector for the Geodimeter Theodolite. ( I can't remember the model number.) This would have been in the early 1980s.

Esentially it would have captured data in the form of rectangular co-ordinates or polar co-ordinates straight from the Theodolite.

Some Surveyors used straight HP 41 calulators as data recorders and wrote their own software. They were never really a great success. There were troubles with the cable connection. For a Surveying instrument the cable connection has to be very robust in order to survive field conditions. Eary GPS units had the same problems with cables. Now days most connections are done by blue tooth.

I never used a Geodat, so I can't really comment on its reliability.


By chance, I have some photos of my unit, I have uploaded them to:


The 1LR4 is a replacement for the 1LB3 HP-IL chip. As far as I know, it is functionally identical to the 1LB3-0003.

The Intel part is a ROMless microcontroller. The EPROM is firmware for that, and the three NEC chips are CMOS static RAM for it.

The "takeover module" mentioned by Klaus must be mounted in the HP-IL module itself. Does the HP-IL module look like it has been cut open and glued back together?


Hi Eric,
I posted the link to the pictures of my unit after you replied. It seems that my unit has the same hardware as the other unit, so it guess the other unit will require the takeover-module (which is in a standard HP-41C module housing), as well

Regarding the hardware, I found a reference in "the american surveyor" (the page says november, Copyright 2007, so this is likely to be the issue date) to the hardware, claiming that in 1981 the "Geodimeter 140 Series and GeoDat 126 Data Collector" were introduced. I found the page on the internet, it contains the history of Geotronics titled "A Company of Firsts".

Edited: 15 Mar 2010, 12:46 p.m.

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