The Soemtron ETR 224 Calculator

Manufactured from 1968 to 1974 by V.E.B. Büromaschinenwerk Sömmerda, only about 500 Soemtron ETR 224's were built during the six year production run. The processing logic of the Soemtron ETR 224 calculator, believed to be derived from the ETR220, is all transistorised, consisting of pairs of PNP Germanium transistors coupled as Flip Flops with a few resistors and capacitors, and sets of diodes for gating functions. This particular variant of the Soemtron electronic calculators series had some form of printing capability which according to Rüdiger Kurth was apparently a TSD16. Photos of the printer are available at Rüdiger's website here, near the bottom of the page. It is not known if the ETR 224 retained the 15 digit nixie display or if the printer was internally or externally mounted. More information suggests that a further variant with an internal Streifendrucker, literally strip printer was developed but never went into production.

To date we have found that very little information if any exists about the Soemtron ETR 224, no technical information appears to exist and none of the units are known to have survived.

If you know of any information about the Soemtron 224 please let us know as a matter of urgency here.

August 2008 -
Bernard Green who was Senior Engineer at Office and Electronic Machines in London UK (importers of the Soemtron 220 series calculators) has sent us his recollections of the Soemtron 224 printer mechanism -
"On the 224 we had, the printer was mounted on the top, semi-recessed into the case, and I recall it also had the Nixie tube display. I am beginning to think that we never actually sold a single 224 in the U.K, because either there was no market and / or the printer was too un-reliable. There were photo diodes to detect the position of the print mechanism elements and that they were very un-reliable and prone to ambient light".

"The print mechanism had 16 print wheels with characters and these all rotated on a common shaft. When the desired character was in the printing position, a hammer, one of sixteen, was energised to press the paper against the print wheel. A slotted disc, one slot per character rotated with the print wheels and a photo diode counted the slots into a counter, when the counter matched the digit for a column(s), the hammer(s) were driven. Another slot referenced the home position of the print wheels".

"I can also recall another print mechanism with the characters on vertical print bars. The bars were all lifted by another horizontal bar and then the bar lowered. The print bars came down with the horizontal bar until the required character was in the print position when an electro-magnet for that print bar operated to pull in a pawl hold the bar in position and prevent it falling further. Then, when the bar was fully lowered and in theory all print rods were held by their pawls, a single hammer struck to make the print. For the next row of print the bar was raised again and the individual pawls released as the bars were lifted".

So at this time we have three possible contenders for the printing mechanism on a Soemtron 224 -

1. A rotating "drum" type mechanisim with individual pin solenoids, similar to 1970's and 80's style line printers.
2. A semi-mechanical lever and impact hammer system, likely to have been derived from a previous Soemtron mechanical calculator.
3. A thermal printer.

In the end we may never know for sure what the mechanism actually use was, or if there was a progression of printer types over time, but rest assured if we find out, you will find out from us.