The Drum Dial

The Forgotten Telephone Luminary of the Federal German Foundation Years

Christoph T. M. Krause

• Verlag: tredition
• Jahr: 2020
• ISBN:
  9783347161504
• Thema: Technology & Engineering
• Thema: Engineering General

A journey back to a new beginning for Germany after Hour Zero. Siemens is trying to break new ground in design and technology with its telephone the "Drum Dial", which heralded a new future for telecommunications. But times were changing...

~ VII. APPENDIX ~

01. Patent Specifications.

a. US Patent Office "Döring".

~ VII. APPENDIX ~

1. Patent Specifications.

b. US Patent Office "Madden".

~ VII. APPENDIX ~

2. Manufacturer’s Essay.

Despite the abundance of technical and operational innovations with which the development of telephone technology was generally connected, the external form of the device that the subscriber constantly sees as a symbol of telephone technology, has not undergone any fundamental change for decades.

All common types of telephone in the world are determined in their shape by the round dial of the number switch and have basically retained the resulting shape, apart from certain adjustments due to changing tastes […].

The new Siemens telephone deviates from this frozen form for the first time. In the course of its development, consciously avoiding to combine the components that had become common only in some new taste arrangement. Rather, the technically required steps of handling were individually examined to determine to what extent they are perceived by the user as the least effort. This resulted in three basic conclusions that determined the new shape of the desk phone:

1. A straightforward winding movement of the number switch, in which the dialler's finger can perform a pulling, almost vertical movement, appears psychologically more appropriate than a rotary movement, for the generation of which the finger […, image omitted] must be moved as an axis in the rotating digit hole of the dial. Instead of the circular dial, a dial was therefore introduced as the actuating element of the number switch, in which the ten finger openings lie closely together on a part of the barrel surface.

2. While the number switch can still be operated with an outstretched finger, grasping the handset requires the entire hand. For the user, therefore, the effort of movement is less if the handset is not located behind, but in front of the number switch and the telephone itself can then be more distant from the user than usual. The position of the handset with respect to the line of sight is most favourable, if it does not differentiate between the need for right-handed and left-handed operation, i. e. a longitudinal position of the handset.

3. For acoustic reasons, a small distance between the mouthpiece of the handset and the mouth of the speaker is desirable. With a form of the handset that brings the mouthpiece to the mouth of the speaker, this can only be achieved to a limited extent with the different head shapes for a larger group of people; If there is very little space between the mouthpiece and lips, the participant is somewhat averse to this situation, so that the handset is then deliberately brought into an acoustically incorrect position. The shape of the handset was therefore chosen so that the appropriately shaped mouthpiece is to the side of the mouth of the speaker, so that no discomfort can arise for the user despite a short distance.

In realizing these lines of thought, there were also new possibilities for the design. The new desktop telephone is therefore not only characterized by a number of technical improvements and ease of use, but it also fits beautifully into any environment thanks to its compact and unobtrusive silhouette (Picture 2). […].

Number switch […, image omitted]

The desired straight-line movement when dialling has led to the development of a new type of number switch, that presents the user with the circumferential surface of a dial drum instead of the circular dial disk.

On the cylindrical dial drum there are two rows of five depressions next to each other, which are designated with the numbers 1 to 0 in such a way that the odd numbers are arranged on the left row and the even numbers on the right row. Although the dial drum describes a quarter circle when it is actuated, the dialling person gets the impression that the hand is making an almost straight and almost vertical pulling movement. This and the compact arrangement in two rows of digits results in greater clarity and a shorter elevator path than with the circular dial, so that not only the dialling process is made easier, but also the dialling time is practically shortened somewhat.

The finger depressions of the dial drum do not have sharp edges that rub against the finger, but instead the finger presses on wide contact surfaces that are adapted to the natural curvature of the fingertip. The winding movement is limited by a wide stop surface.

The pulling movement of the finger when dialling, with a direction of pressure which is almost vertical, prevents the desk telephone from tilting or sliding on its surface. It therefore did not need to be made larger or heavier than the necessary installation parts required. This small space requirement and the reduced weight are further advantages of the new design.

The dial drum is injection moulded from thermoplastic material and thus ensures protection against accidental contact with live parts that is important for number switches. It is light and of high form stability. Its position between the walls of the telephone housing, which protrude above them, also protects them from rough impacts.

The number switch works like all newer versions with idle speed, that means the pauses between the dialling of the individual digits are inevitably extended by the duration of two current pulses, i. e. by about 0.2 s. It runs at the usual speed of 10 +/- 1 current pulses per s [second]; the apparently slower return of the dial drum compared to the circular finger disc results from the shorter distance, the drum has to travel towards the finger disc. The current surge ratio is 1.6: 1 (opening: closing).

The contact mechanism and drive of the number switch are based on the construction parts for speed control and contact control that have been tried and tested in previous versions. These are combined in a housing made of light metal injection moulding, in which the selector drum is also mounted. The entire control unit is protected against dust by a cover.

Handset location

In the idle state of the telephone, the dialling drum is covered by the handset lying on top of it in the longitudinal direction. This handy longitudinal position of the handset, which contributes significantly to the compact structure of the telephone, brings various advantages: the handset can be lifted with the left or right hand equally well and without changing the position. Its length blends largely into the silhouette of the telephone.

The previously used cradle for the handset has been replaced by a plate-like rest. The earpiece of the handset rests on this support plate, while the mouthpiece is...

Inhaltsverzeichnis

• Cover
• Title Page
• Copyright
• Contents
• Dedication
• ~ I. A Personal Prehistory ~
• ~ II. Patenting the Drum Dial ~
• ~ III. the History behind the Drum Dial ~
• ~ IV. Structure of the Drum Dial ~
• ~ V. the Exterior of the Drum Dial ~
• ~ VI. Weaknesses and Strengths ~
• ~ VII. Appendix ~