Soemtron.org - Time line (previous)

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!.

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.

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 beastie, 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 fewer and 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.

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.

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 -ve numeric entry, or the #n (raise to power) functions.

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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