Diode-earth method

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The diode-earth method ( DEV ), also known as direct current push-button selection , is a signaling method that is no longer used in telecommunications technology. It is a DC voting process; In addition to the two speech wires (a-wire and b-wire; see also a / b interface ) an earth wire (the so-called earth ) is required.

DEV was a voting system for early pushbutton telephones. It was not widely used and was superseded by the multi-frequency dialing method (MFV) in private branch exchanges (such as Siemens EMS) in 1979 .

scope of application

The diode-earth method was used in the 1960s and 1970s for extension telephones on specially suitable telephone systems (e.g. Siemens ESK 400E, ESK 3000E and GWN / EMD). In the case of private branch exchanges, the ground wire was required to obtain an outside line and / or to make inquiries. The JY (St) Y cables commonly used in private extension technology carry the earth potential in the shield wire.

DEV was not suitable for use in the public analog telephone network of the Deutsche Bundespost with the large connection line lengths because of the asymmetrical principle. Line influences occurring due to the asymmetry limit the functional range. The advantage of DEV was the relatively little effort required in the telephone set, but telephone systems no longer support DEV since the early 1980s.

In Austria, the DEV1 procedure was only used in the public network at a research office in Vienna's Zollergasse, but was soon abandoned and replaced by the MFV procedure that is still used today. In total, only around 150 connections were equipped with this dialing method.

functionality

Basic circuit diagram DEV

The choice (more precisely " signaling ") is made using the keys of a keypad . When the keyboard is operated, 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 button 8 is pressed, contacts II and IV are closed (see block diagram). By pressing a button, different switching criteria (number and direction of the switched diodes) are created, which are evaluated by the switching device (telephone system). The switching device determines the pressed key by alternately applying minus voltage and plus voltage. The key must be pressed for at least 50 ms so that the switching equipment can reliably determine the key press  .

The ability to combine four diodes as required results in 2 4  = 16 possible states. However, since the combination (0, 0, 0, 0) for contacts I to IV means “no key pressed”, only 15 key states remain, of which 12 are used (0–9, *, #).

Function table
button 1 2 3 4th 5 6th 7th 8th 9 0 * # unused
Contact I. • • • • • • • •
Contact II • • • • • • • •
Contact III • • • • • • • •
Contact IV • • • • • • • •

literature

  • Dietrich Arbenz: From drum selector to Optiset E. Herbert Utz Verlag GmbH, Munich 2009, ISBN 978-3-8316-0908-6 .
  • Harald Schumny: Signal transmission. 2nd revised edition, Friedrich Vieweg & Sohn, Wiesbaden 1987. ISBN 978-3-528-14072-4 .

swell

  1. ↑ Gert Kaszynski, Jürgen Schönhoff: telephone terminals . VEB Verlag Technik Berlin.

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