Our refurbished Soemtron 220

and it's original condition !

Soemtron ETR 220

Coming soon to a browser near you - the Soemtron ETR 220.
We have the technology, we have rebuilt her ! - >>>>>>

This website is dedicated (in probably a very nerdy way !), to an old piece of calculator history received in 2007 from Prague in the Czech Republic, after a Google search for "core memory" during some research into the PDP-7 range of computers manufactured by the now defunct Digital Equipment Corporation. The unit duly arrived, but it was found to be in a very poor state, dirty, rusty and missing its power supply and top covers (see the bottom picture). After a few days research and translating some German text off of the baseplate, we worked out what this old dirty corroded hulk was - a Soemtron ETR 220 calculator, which turns out to be a very interesting piece of early electronic calculator history from 1960's and 70's German Democratic Republic.

A typical Soemtron ETR 220

Over time we repaired and conserved our Soemtron 220 and eventually we hope to get into working order this interesting piece of Eastern Bloc calculator history from the 1960's (see the top picture). Bookmark this page and come back from time to time for a visit and see how we are getting on. We have published and are updating a full circuit diagram of the machine and its inner workings for those of you who are interested - not many probably !, but there again this is the Internet, see you again soon.

The third picture (left) is of a very good condition Soemtron ETR 220 owned by calculator collector Serge Devidts, for more information see his website here

Time line -
Older news from soemtron.org can be found here.

Keyboard microswitches

June 2009 - We are looking for a supplier of the keyboard microswitches used in the Sometron 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 unuseable. 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

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. Eighty six pages have been done to date, out of 214. Russian manual - 2.9Mb pdf

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.

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.

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.

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 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.

Click here for previous events in the Soemtron website time line.