soemtron.org - Time line

September 2009 - soemtron.org recently drove out to Germany to pay a visit to the Historisch-technisches Museum in Sömmerda to see the museum and meet with museum volunteers and a few ex-workers from the Soemtron factory. See the 224 and Sömmerda 2009 trip pages here for further information.

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August 2009 - Translation of the Russian manual completed - the latest version is here here - (10.8Mb pdf). This manual has been reproduced from a 1972 Russian publication, we recognise the copyright of the original publisher.

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July 2009 - A small milestone ! - over one hundred pages of the Russian manual have been completed ! - actually 170 out of a total of 214, so a little more work to do. You can read the current version here - (4.1Mb pdf). This manual has been reproduced from a 1972 Russian publication, we recognise the copyright of the original publisher. There are a dozen or so few words in the translation that are not recognised by the translation software no matter how much we tweak them, so if there are any Russian linguists or speakers out there - can you help ?. In the translated pdf file the words are bold in red between square brackets. - Eg. [word]. Any help is much appreciated and will be credited on site.

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Keyboard microswitches

June 2009 - We are looking for a supplier of the keyboard microswitches used in the Soemtron 22x series of calculators, said to be V23 microswitch ?. One of our machines, the 222, has several broken keyboard switches, which because of the connection arrangement, renders the machine unusable. They may be of German origin, they have the triangle 1 quality mark, are rated at "220V~2,5A", and a "C2"mark. The manufacturers logo is an inverted V in a circle.

We have designed an alternative drop in replacement which would retain the old switch body and use a V3 style microswitch in place of the contacts, but as this means some delicate machining and wiring we would like to find the correct or compatible parts first. A drawing of the switch can be found here.

If you have any information about these switches please contact us here, or email us .

(Update October 2009), following our visit to the Historisch-technisches Museum in Sömmerda, we have managed to contact a supplier and obtain a small quantity of used but functional switches.

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May 2009 - Full time work on the Soemtron 220 has not resumed yet, but we have started on that Russian manual received from Gerhard Just back in July of last year. Some time was spent searching the web for a decent OCR program for Cyrillic characters and eventually we found one that does a very good job, so we have started on this bit of the project.

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March 2009 - Due to other pressing matters (we have to work !), work on our Soemtron 220 was suspended in January but is expected to resume in April/May. This is a bit of a shame as we had just got to the interesting bits, examining signals and relating them back to the circuits, never mind, we will be back soon. Meanwhile if you come across any other snippets of information about the Soemtron 220 / 222 /224 machines please let us know.

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February 2009 -
23/2/2009 - Ruediger Kurth finds a Soemtron 224 in the archive of a Söemmerda museum, at this time this is the only known Soemtron 224 in existence !.
19/2/2009 - Information on the 224 page updated with an email reply about the printing mechanism from the Historisch-technisches Museum at Sömmerda.

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January 2009 -
Firstly - a Happy new year to all, we hope you had a good Christmas break.
Next - is there a helpful person out there ?, one who could help us out by translating the Russian Technical Manual received last year. It is online here, (10Mb pdf), and whilst we can get the gist of the diagrams, the rest of the document eludes us !. It appears to be a full description of the Soemtron 220 and it's inner workings, and any work on the manual will be credited in full, so, any takers - please ! - contact us here.

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December 2008 -
With the extender board finished and now the monitor board completed, work on expanding the circuits and logic diagrams is progressing well. We have got the shipping damage to the second 220 repaired and it's now operational, so this machine is the basis for the work on the internal logics of the 220, keep an eye on the downloads page as new copies of the drawings will be up-loaded as they are completed.

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September 2008 -
The Russian Technical Manual received a few weeks ago is now online here, (10Mb pdf) or from the normal "Downloads" page. Now we can't read Russian, but this appears to be a full description of the Soemtron 220 and it's inner workings, including a basic description of the logic elements, their component values, operation and even a timing diagram or two. A multi-page scan of an overall logic diagram is included here, (1.4Mb pdf) or again from the Downloads page.

Bernard Green has turned up a but more information about the Soemtron calculators from the Büromaschinen Lexikon, or the Office Machines Encyclopedia, published during 1957 to 1986 it was the required publication to be listed in for a calculator manufacturer. The Soemtron 220 series machines were included in the B.M.L. from 1962 to 1968, described thus (© 1968-9 Goeller Verlag) -

1966/7 issue - "Both models implement the 4 basic operations of arithmetic and powers. Rounding of the last number with multiplication and division, variable decimal point, 3 free memories with addition and subtraction, memory recall with or without deletion, constants, endaround carry, negative result indication, fast printer. 15 digit display, printing to 18 place with decimal point and symbols. Keyboard inhibit during overflow. A unit with keyboard and printer but without the arithmetic unit can be connected to a display model as a slave computer."
Cost - Soemtron 220 : DM 5800, Soemtron 221 : DM 7500

1967/8 issue - "The Soemtron 220 is a display indicator model, with a second variant with keyboard and printer. Both models have the four basic operations of arithmetic and powers. Rounding of the last number with multiplication and division, variable decimal point, three free memories with addition and subtraction, memory recall with or without deletion, constants, endaround carry, negative result indication, fast printer."
Cost - Model 220 with display: DM 5300, price of the printing model: DM7200

So yet again we have a bit more confusion !, a model 221, with a printer and that could act as a satellite to a model 220. Both of these entries in the Lexicon are dated from before the apparent date of the 224 production run (1968 to 1974), so they may be precursors and not quite the same as the final 224 product. It makes sense to have the first model as a 220, and then to have a printing unit as a 221, then introduce your next model as the 222. Perhaps the 221 was dropped and they decided on a 220, 222 and 224 sequence - who knows - if YOU do, please let us know here.

A couple of small milestones reached with the original Soemtron 220 and extender board, both have been finished !. The original 220 that started this all off is now back together and fully assembled, photos can be seen on the Gallery page, she looks quite good even if we say so ourselves, all the dirt, dust, rust and crud has all gone and without a respray she is as near to original as we can get her. The power supply wiring has been replaced ready for a new power supply when we get down to building one or can find a donor machine. The extender card is also finished and this can also be seen in the Gallery, so we can now start on debugging the second Soemtron 220 and also the 222. The next item for the extender is a small signal monitor PCB that we are waiting on delivery from the suppliers, this will then allow us to monitor up to eight signals and / or flipflops without resorting to using an oscilloscope. About two weeks should see this bit of the project complete.

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August 2008 -
Work on the extender board is progressing, connector PCB's have been assembled into their mating plug and socket parts and the metalwork is currently being cut ready for assembly. The monitor board design is basically complete and has been bread boarded to check out the op-amp and comparator circuits. A small DC-DC supply circuit remains to be tested but has not yet been completed, once done, the monitor PCB design will be finished and sent for manufacture while the extender is wired up.

Meanwhile we have completed translating the user manual "Electronischer Tischrechner Soemtron 220 - Bedienung und Ubung" that we found back in February. You can view the current result here. Please bear with us as German is not our first language and we are using an online translation engine for the basic work, there ARE mistakes !. This book is copyright 1972 Manfred Sperfeld of V.E.B. Counting Machines, Potsdam.

Then there is the Russian manual to do.......... (see below)

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July 2008 -
Gerhard Just sent us a contact form this month, he has a Russian manual for the Soemtron 220 but no machine!. He has very helpfully scanned the manual and sent it over for us to look at, it appears to have the same logic diagrams but also some other different information that we have not yet seen. Translating this will probably become yet another project for us to embark on, but not for now, we will just make the pdf's of the scans available in a few weeks time. Many thanks to Gerhard for his help!.

Ruediger Kurth has emailed in with kind comments about this site and a bit of information about the Soemtron 224. The printer for a 224 apparently was a TSD16 and photos of the printer can be found at Rüdiger's website here, near the bottom of the page.

Circuit diagrams are now complete - at last !, and just about on schedule (from our original prediction of the middle of 2008), any minor modifications to the circuits from the logic diagram generation process will be uploaded as required. Logic diagrams have been started with the diagrams for Boards 11 and 12, each with their respective sections of the Display and Keyboard. They can be found online on the Downloads page. Currently work is progressing on getting an extender card built so that we can start examining the signals on and around the boards and determine actual logic levels. A supply of suitable pins (H2170-01) and sockets (H3194-05) has been received from Harwin and our grateful thanks go to them for their help with this project. We have used their products in the past and can highly recommend them. A pcb for the extender board is currently in manufacture and should be with us soon. The extender board is envisaged to have a small ancillary adjustable LED monitor pcb so that we can examine the state of slow moving and stationary signals, although the design of this circuitry is not yet done. The extender board design will also be available from this website when we have completed it.

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June 2008 -
Circuits for the original Soemtron 220 are almost complete - honest !. We have pretty much finished the drawing and checking of the circuits and with only a couple of snagging points for boards 8 & 9 to be completed we have pdf'd the circuits and uploaded them. Any changes for boards 8 & 9 will follow in a few days. These circuits represent 10 months of work to reverse engineer the boards of our original Soemtron 220 and at this time we believe they are as complete as they can be. Over these last few months and especially since Bernard Green sent us the original logic diagrams to check against, we have found that there are several errors in those original German logic diagrams which are mostly down to typos in the net names, the next job is to produce a set of modern logic diagrams using current symbols.

A recent Email from Thomas Richter has helped out with yet some more information about the Soemtron calculators - that being the operation of the top row of three register operand keys. We had them down as being "multiply" keys, they are actually combined action "Recall" and "Clear" keys. As Thomas says "Pressed once, the value of the appropriate memory is displayed, once again, the memory is deleted". Also Thomas mentions that "pressing Lö does not affect the content of the 3 memories". Many thanks to Thomas for his help and also correcting our German wording for us - oops!.

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May 2008 -
We have at last finished the initial transcription of the circuit boards from our Soemtron 220, but that's not the end of the saga !, we are now cross checking all the circuits against the logic diagrams sent by Bernard Green, correcting any anomalies. Once this is done we will then update and produce new logic diagrams using modern equivalents, as although supplied with a logic table, most of the original symbols do not conform their the more widely recognized modern equivalents. Then comes the task of designing and building a power supply and getting this original Soemtron 220 of our collection working. As you will appreciate a bit more work to be done.

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April 2008 -
This month we received a partially working Soemtron ETR 222 serial number 74005 from an Ebay sale in Germany, quite a rare little beast, although not a rare as a Soemtron 224 !. These 222 units were apparently in production between 1970 and 1972 with only about 3000 of them being built. On examining the machine the date stamps would appear to be for 1968, and on closer inspection it seems that most of the boards are labeled with a "224" root part number, a much rarer machine !. This Soemtron 222 seems to be a real Chimera as it has boards from all three variants of these machines (Soemtron 220, 222 and 224). This 222 is partially working, having a couple of broken keyboard switches which renders it unable to properly calculate due to the series switch connection design of the keyboard, but ultimately quite repairable - we hope !.

Now this leaves us with a problem, is this machine actually a Soemtron 222 ? (outwardly it looks like one and it is marked "Soemtron 222" on the case), a converted 224 ?, or a Soemtron 222 with common boards from a 224. This little problem is going to take quite a bit of research, but whatever the outcome it seems that the generally accepted information out there on the Web for production run dates of the Soemtrons could be wrong, if this machine is a Soemtron 222. On the other hand it could be a Soemtron 224, but where does the printer connect ?, no extra connectors are in evidence. The Soemtron 222 calculators apparently have seven but different functions, than that of the Soemtron 220 (from the keyboard diagram in the book mentioned below), but it appears to have much more circuitry and logic than a Soemtron 220. The display driver and keyboard encoding circuits are moved to another set of extra boards below the keyboard, so making space in the card cage for the two extra logic boards (eleven and twelve) that this machine appears to have. We will eventually investigate this "Soemtron 222" but not until we have finished our fun and games with the original Soemtron 220.

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March 2008 -
Bernard Green who, some years ago was Senior Engineer at Office and Electronic Machines in London UK, who were the importers of the Soemtron calculators from the D.D.R., has helpfully sent us copies of the logic diagrams for the Soemtron ETR 220, pdf copies of the diagrams can be seen here, they include component references and values, logic symbols and a diagram for each board. They give an insight into the what the Soemtron logic designers were able to achieve in the functions of the Soemtron ETR 220 with such basic, albeit almost primitive electronics then available in the 1960's in the German Democratic Republic. As Bernard states "That sort of design skill is being lost (or has been lost) now that processors with bloatware do so much". Many thanks to Bernard for all the help he has given.

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February 2008 -
A recent Email from Philipp Maier included another snippet of information about the Soemtron calculators - some of them are marked with a "Quality" symbol on the rear of the chassis, a number in a triangle, with 1 being the best and 3 the lowest. It would appear the first unit we bought missing its case and power supply has a quality mark of 1, whilst the second unit complete and working has no quality marks at all !. Comparing the two machines, the second one does seem to have a much worse standard of assembly.

We have been contacted by Bernard Green who some years ago was senior engineer at Office and Electronic Machines in London UK who imported the Soemtron ETR series of calculators from the D.D.R. He has various bits of information about the Soemtron 220 and has already passed some of it on to us for incorporation into this website. Watch out for more information to come in the future. Reverse engineering of the boards is progressing, currently at about one a month with other things on the go (like life and work!), Board 7 has just been finished and this also includes a few minor corrections and additions to the Backplane and other circuits.

We have now found and had delivered to the UK, a guide to operating the Soemtron ETR 220 with some working examples and exercises, some of them quite complex. Printed in 1971 the book is entitled "Electronischer Tischrechner Soemtron 220 - Bedienung und Ubung", and as you may have guessed from that it is in German !. It will need translating unless we manage to find an English version - so, are there any volunteers able to assist with the translation ?. Just for now that title in English is - "Soemtron 220 Electronic Desk Calculator - Operation and Exercises". From a cursory look through the 63 pages it would seem the Soemtron ETR 220 is capable of some very complex calculations, especially from a veteran calculator with only six functions. There is also a small diagram at the back showing the keyboard layout for a Soemtron ETR 222, which as far as we can gather did not have the negate entry, or the #n (raise to power) functions.

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January 2008 -
We have received another Soemtron ETR 220 this time from Germany where they seem to be reasonably common, it has a serial number of 54555. Unfortunately it was damaged in transit and will need repair before we even dare to turn it on, however it does have a complete power supply, so we can use this as a model to replace the power supply on our original unit.

An excellent technical description of a Casio AL-1000 calculator has been found on the web here, the Casio AL-1000 in some respects would appear to be similar in a way to the Soemtron ETR 220 and it is hoped that the technical description of the AL-1000 will go a long way in helping us to decode the inner workings of the Soemtron ETR 220. Many thanks go to Brent Hilpert for publishing this information and the technical contents of his excellent website which can be found here.

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