The Soemtron Calculator Collection

Our refurbished Soemtron 220

and it's original condition !

The Soemtron brand of calculators encompassed three and possibly four calculators, the 220, 222, and a printing calculator the 224. Contemporaneous literature of the period does describe and show a type 221 printing calculator believed only to exist as a publicity release (see December 2009 below) in the Büromaschinen Lexikon, a German publication of the 1960's.

This website is dedicated to the Soemtron electronic calculator range and came into existence when an old piece of equipment was 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 have repaired and conserved our Soemtron 220 and eventually we hope to get this interesting piece of Eastern Bloc calculator history from the 1960's (see the top picture) into working order once we can get a power supply into her. 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 full circuit diagrams 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

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

Original Thüringer Allgemeine article English translation here

May 2010 - We make the local press in Sömmerda. This article 15.05.2010 (in German) from Thüringer Allgemeine's Sömmerda website describes several trips to Sömmerda after contacting the Historisch-technisches Museum, our interest in the Soemtron machines, on obtaining vital connectors, and finding an ETR 224. We have now received a scan of the article as printed in the paper - pdf copy here - and shows Bernard (at left) and Mike (bearded) during the September 2009 visit. A few very minor errors in the article, but we are very glad to have made the local Sömmerda press !.

The Historisch-technisches Museum's new technical archive building in the Uhlandstraße is very close to completion and will soon feature all of the BWS Sömmerda machines and documentation that have been in storage for so long, including several examples of the Soemtron ETR calculators. The almost complete archive was recently opened to the public for one day as part of the International Museum Day campaign.

We now have some connectors !. In another trip recently made by Bernard to Sömmerda, a small supply of Daro20 and Daro32 connectors was found, so this will allow us to build test equipment similar to that used in the factory. During the trip Bernard again met with people from the factory and also managed to pick up a book entitled "BWS Sömmerda", written by Annegret Schüle (ISBN 3-9083931-1-9). Pictures from the book show the 220 production line and the test equipment, and after a little research we have found the copyright owner and can now let you see the pictures, they are in the main Gallery page. We also picked up another ETR 220 for use as spare parts.

Cleaning the ETR 224 we picked up last September is progressing well, all the case parts are being re-sprayed as the were heavily corroded. The printer mechanism is now clean and being reassembled, but we found one of the print wheel arms was bent and would not contact the idler gears or the platen properly. This bent arm has been fixed and re-assembly continues with the worn fan bearings.

Typical connectors

Soemtron connector logo

February 2010 - Following the great help visitors to this site have given in the past, we are now looking for some connectors - can you help ?. The photo (right) shows a typical set of connectors used on the Soemtron calculators in 32, 20 and 11 pin sizes of both male and female types. The main body of these connectors would appear to be porcelain, although the black link plug (2nd from the top in the photo) is a plastic material. The 1.0mm diameter pins are on a staggered three row 3.0mm pitch format, and they "float" in the connector housing allowing for a small amount of mis-alignment on insertion. A mechanical drawing of a Daro20 plug can be found here. Text on the side of the connector body is - Logo, ?, quality standard 1, 3 amp, Silver (plated), ?.

These connectors were apparently a special standard to the Robotron brand, with cable connectors available in both plug and socket versions (photo examples here top of the page) listed as the "Daro20" and "Daro32" connectors. We think however, that this connector style may have been available elsewhere, as we have seen similar connectors used in the British MOD on electronic systems, where they had sheet metal back shells with a floating external cable clamp (Pye or Plessey comes to mind ?). A few years ago there were articles on the web about the 40th anniversary of the invention of the mouse by Doug Engelbart, which used the same style of connector, see this page at Tech-E-Blog.

If you know anything about or have any information on the Robotron "Daro20" and "Daro32" connectors please contact us here, or email . We are looking for two sets of male / female connectors in the "Daro32", and one set of male / female set of what would be "Daro11".

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A Soemtron 221 Picture ©2009 Serge Devidts

December 2009 - After some research by Bernard Green and ourselves, about a possible ETR 221 unit, a recent email from Serge Devidts has confirmed the existence at some time in the past of a two part printing calculator, the ETR 221. Bernard had suggested existence of the 221 a while back having said that he recollected a unit had been shipped into the UK whilst he was at Office and Electronic Machines in London. He described the 221 as a two part machine: a desktop unit with keyboard and top mounted printer, and a second unit connected by an umbilical cable to the main electronics section. The only reference to this split personality machine was a vague picture in the Büromaschinen Lexikon for 1967-68, however the receipt of Serges' picture (right) has shown both sections of a 221 connected by an umbilical cable and large connector.

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

The Soemtron 220 range also appeared in the "Büromaschinen Lexikon", a German publication covering office machinery and products. Soemtron branded products appeared in the 1962/63 to 1968/69 issues, but only three are available online below -

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