Identify this keypad

[leejor]

So, I was given, what I assume is a German (Siemens) desk phone. It has, what at first appears to be a DTMF keypad. However, it has no components other than 4 blue (two pin)"chicklet" sized devices on the circuit board. There are no other electronics on the keypad circuit board. The keys operate some common contacts on one side, and a combination of contacts on the other side. However it does not operate two sets on each key press,  It can be one,two or three. I get no tones when pressing the keys, (both polarities). I have never seen a DTMF keypad like this, it seems to be too simple.
Anyone familiar with what this is?
Thanks.

[G-Man]

D.C. keypulsing as used on some PBXs manufactured by Philips/Norelco and certain other European manufacturers? Or is there a chip on the main board that generates DTMF signals?

Is there a model number stamped underneath the set? 

Have you tried to Google the part number on the keypad?

[poplar1]

Pushbutton dials in the U.S. that generate dial pulses do not have a * or #. (For some ESS feature codes beginning with *, one can dial 11, for example 1169 or *69 = Call Return (to call the last number that called you, so long as it is not a call from a cell phone).

[G-Man]

Yes, though the system that I am referring to was not pulse based and had 12 buttons, with two for special functions.
 
It wouldn't be too hard to imagine that the newer generation of keypads retained the octothorpe and star symbols for those special functions.
 
 IIRC, these PABXs were still being made well into the 1980s. I believe later dials had reed switches incorporated on the pad's circuit board.
 
Philips/Norelco "developed a direct current (DC) signaling method for dialing telephone numbers, for use in the UB-49 private branch exchange (PBX) system. The push-button dial pad used an arrangement of semiconductor diodes to produce a distinct sequence of polarity states for each dialed digit between the two line conductors and ground return, which were analyzed in the exchange by relay logic.
[snip] the system was used in the UK, when the General Post Office (GPO) introduced the first UK-made push-button telephone, the GPO 726 (Ericsson N2000 series)."
 

[leejor]

There is no chip, or any other electronic components on the circuit board other than the four small blue devices (and the contacts). The blue devices all seem to be identical as there is no uniquely identifiable makings.

[tubaman]

There is no chip, or any other electronic components on the circuit board other than the four small blue devices (and the contacts). The blue devices all seem to be identical as there is no uniquely identifiable makings.

As the 'blue devices' have polarity markings they will either be diodes or capacitors, and I'd say more likely diodes in this case.

[G-Man]

As the 'blue devices' have polarity markings they will either be diodes or capacitors, and I'd say more likely diodes in this case.

Yes, and it's interesting that Siemens removed the markings from them and omitted the model number and nomenclature from the bottom plate underneath the instrument.
 
Otherwise clear, well focused photos of them would possibly help greatly in unraveling its identity.
 
However, based on what has so far been described, the D.C. signaling scheme, which was employed by some European telecom manufacturers for PBXs and certain intercoms, is now seeming to be an even more plausible explanation.

I had been hoping that some of our fellow Continental collectors would be able to recognize it and tell us more about its use, including what the function of the two unmarked buttons on the housing are.

[G-Man]

Here are snippets of a post made in 2001 regarding such a system:
 
"Has anybody ever heard of dc current pushbutton dialing [DCPB]?
 
It was supposedly a Dutch PTI (Philips Telecommunications Industry) invention. It was only used in non public telephone exchanges.
 
North American Phillips (Norelco) sold UH type PABXs in the USA during the '60s. UH employs a common motor to drive multiple uniselectors.
 
Since private ownership of PABXs was not yet permitted at the time, these systems for the most part were sold as PAXs by omitting the CO trunk ckts. Some of them used DCPB dialing.

 I believe Norelco also attempted to market the full PABX version to [U.S.] independent telephone companies. I'm not sure how many were actually sold. DCPB dialing on a PABX would require the provision of register-senders within the PABX equipment for compatibility with the CO, to convert calls dialed out of the PABX to conventional loop-disconnect dial pulsing.
 
Since Touchtone was coming into widespread use in the USA at this time it's possible that DCPB was used only on PAX systems for this reason. It's much more economical than TT for an isolated system while TT is much more economical for a PABX.
 
 Norelco was also active at this time in offering TT conversion systems for retrofitting existing PABX and CO switching equipment. Therefore they would have had register-sender designs available which could have been applied to either DCPB or TT dialing.
 
The only information I have is a very very brief description of the system in Dutch with a few diagrams.
 
There was extensive discussion about this system perhaps a year or more ago on the Strowger list. I believe the same or similar technique was used in the UK by other mfrs. Perhaps elsewhere in Europe too. I think LME and others used a compatible or at least similar system.
 
I have an LME "Dialog" style set which I believe is also compatible."

[countryman]

German keypads sometimes used to have # and * with no functions.
I suppose yours is a Siemens Masterset 111 (see attachment). They came with all kinds of dials including dc diode types (called DEV in German).
Sometimes the circuit boards were identical and allowed for different dial types. A schematic can be found in this thread of the German forum: https://www.wasser.de/telefon-alt/forum/index.pl?job=thema&tnr=100000000006148&seite=97&begriff=&tin=&kategorie=
It does not show your exact model but a similar one.
Or try https://www.wasser.de/telefon-alt/datenbank/inhalt-bilder/bb1000771.jpg?1708976767
for schematics.
The DEV keypad is only useful with a PBX designed for exactly this. German Wikipedia link: https://de.wikipedia.org/wiki/Dioden-Erd-Verfahren

[leejor]

Thanks, You've solved the "mystery". I had assumed that it was probably meant to be used on a PBX of some sort but had never seen anything like this in the past. Since it was only used on a few European PBXs, for a short while, there was even less chance of running into one here in North America.

[G-Man]

it was only used on a few European PBXs, for a short while

No, this system was also used in Norte America!
 
About 15-20 years ago I briefly owned a Norelco (North American Philips) PBX that used sets with D.C. Signaling before I ended up giving it to another switcher.
 
Remember "Clean up on Aisle Three!" or "Price Check on Mrs. Paul's Fish Sticks?"
Some U.S. supermarkets (and other businesses) used smaller intercoms that were tied into their paging systems that often employed D.C. Signaling, since it was cheap and reliable. They were generally mounted next to the cash registers, in the stock room, manager's office, etc.
 
I think the bigger mystery is why there are no markings showing the model number of the set.

[5415551212]

German keypads sometimes used to have # and * with no functions.
I suppose yours is a Siemens Masterset 111 (see attachment). They came with all kinds of dials including dc diode types (called DEV in German).
 German Wikipedia link: https://de.wikipedia.org/wiki/Dioden-Erd-Verfahren

Very interesting thanks for sharing.
That wikipedia page translates to:

In the 1960s and 1970s, the diode-earth method was used for extension telephones on specially designed telephone systems (e.g. Siemens ESK 400E, ESK 3000E and GWN/EMD). In the case of PBXs, the earth vein was needed anyway for official retrieval and/or query. The J-Y(St)Y cables, which are common in private extension technology, carry the ground potential in the shield bywire.

DEV was not suitable for use in the public analogue telephone network of the Deutsche Bundespost with its large connecting cable lengths due to its asymmetrical principle. Line interference due to asymmetry limits the range of functions. The advantage of DEV was the relatively low effort in the telephone set, but telephone systems no longer support DEV since about the early 1980s. In Austria, the DEV1 method was only used in the public grid at a testing office in Vienna's Zollergasse, but was soon abandoned and replaced by the MFV procedure that is still in use today. In total, only about 150 lines were equipped with this voting procedure.


The selection (or more precisely, "signalling") is made by means of the keys of a keypad. When the keyboard is pressed, one or more diodes are switched on between the a-wire, the b-wire and/or the earth wire, depending on the key pressed; for example, when key 8 is pressed, contacts II and IV are closed (see principle diagram). By pressing a button, different switching criteria (number and direction of switched diodes) are created, which are evaluated by the switching device (telephone system). The switching device detects the pressed key by alternating the negative voltage and positive voltage. In order for the switchboard to reliably detect the keystroke, the button must be pressed for at least 50 ms.

The arbitrary combinability of four diodes results in 24 = 16 possible states. However, since the combination (0, 0, 0, 0) means "no key pressed" for contacts I to IV, only 15 key states remain, of which 12 are used (0–9, *, #).

[leejor]

We generally only saw Nortel or Mitel PBXs before things began changing over to VoIP. Being in Canada, providers would tend to go with a "local" supplier. There were the odd Plessey (in the '70s), and Hitachi (crossbar) system that would pop up once in a while.