Improvements in and in connection with Telephonic Microphone Apparatus for Electric Signalling.
Year: 1898

page_text: Date of Application, 10th Dec., 1898-Accepted, 4th Feb., 1899
COMPLETE SPECIFICATION.
Improvements in and in connection with Telephonic Microphone
Apparatus for Electric Signalling.
We, SIEMENS BROTHERS & Co. LIMITED, of 12, Queen Anne's Gate, Westminster,
S.W., Electrical Engineers, do hereby declare the nature of this invention (as
communicated to us from abroad by Siemens & Halske Aktien Gesellschaft, of
Markgrafen Strasse, No. 94, Berlin, S.W., Electrical Engineers) and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement;
For transmitting telegraphic signals a "buzzer is often employed in place of
an ordinary Morse sounder if it is desired to render the signal audible only in the
immediate neighbourhood of the instrument.
According to the present invention the microphone of a telephonic installation
is rendered available as a buzzer for telegraphic purposes, while it is also
available for transmission of speed.
For this purpose the known fact is made use of, that a microphone membrane
can be set in vibrating motion by means of a telephone in immediate proximity
thereto and connected in circuit therewith, the membrane of which telephone
is set in vibration either mechanically or by atmospheric undulations, the said
vibrations of the microphone giving a buzzing noise which can be telephonically
transmitted to another station.
According to the present invention a single membrane is made to fulfil both
the functions of the above arrangement.
For this purpose the apparatus is constructed as follows:
Referring to the accompanying diagrammatic drawing, the microphone M is
one of known construction, the membrane A of which is made of thin soft
sheet iron B is the microphone bag containing carbon granules, and
secured in the usual manner.
fitted
The membrane is
on a cup C
of soft iron, and the bag B is closely surrounded by a hollow
cylinder 1, also of soft iron, fixed rigidly to the cup C. On this cylinder is
mounted a wire coil E. F is the usual sound plate or mouth piece. The induction
coil,G required for the microphone M consists of a primary coil H and two
secondary coils J J, of which conveys the induced current through the tele-
phone T to a distance while the induced current from J passes through the
coil E, so that the membrane operates by telephonic action.
This current however only passes into the coil when the circuit that can be
interrupted by the switch device U, is closed.
This switch device consists essentially of a slide on which are three insulated
contact pieces having different relative positions to each other. The slide can
be moved into two distinct positions, in one of which (shewn in dotted lines) two
contact pieces thereof, K' K³, make contact with two contact blocks while
in the other position (shewn in full lines) only the third contact piece K² makes
contact with the contact block ².
In the first named position of U the coil E is put into circuit and the apparatus

page_text: then serves for telegraphing, while in the second named position of U the apparatus
is arranged for telephonic speaking, the "buzzer" device being then used for
calling. L is a switch by means of which the battery N. can be put in or out
of circuit. The circuit of the current will be as follows for the two different
functions. When the switch device U is moved back as shewn in full lines on
the drawing, only K2 being in contact with 3, E is out of circuit, and the apparatus
is ready for speaking purposes. The current passes from battery N for instance
through lead 1, primary coil H lead 2 bag 13 membrane A lead 3 switch L, lead 4
Morse key O lead 5, contact block contact K2, lead 6 and back to battery N.
If the switch device U is in the forward position, making contact at k¹ and ³
the contact at 2 is broken and consequently the lead 5 is out of circuit, while E
is connected to the secondary coil J. If now the circuit be closed by the key O
an induced current will be produced in the secondary coil J as follows:-by the
closing of the microphone circuit by means of key O a current impulse will be
passed through the primary coil H and a short induced current will be produced
in the secondary coil J.
This will excite the telephone coil E whereby the iron membrane A is attracted.
By this motion the resistance of the microphone is varied and a second current
impulse is produced in the secondary coil J which again causes E to actuate
the membrane, and this is repeated as long as the key is pressed down.
By the rapid succession of the varying current impulses the vibrations of the
membrane, which are always reproduced with the same force, are strengthened
so that a buzzing sound is produced. This sound is transmitted telephonically
through the coil to the distant station, so that by the usual long and short
duration of the depressions of the Morse key corresponding long and short
buzzing sounds are given. These, of course, can be transmitted according to
known codes.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is
1. Microphone apparatus for electrical signalling by buzzing sounds wherein
an iron membrane is so combined with a microphone and a telephonic electro-
magnet coil, that induced current impulses controlled by a Morse key and passed
through the said coil are made to produce vibrations in the membrane by magnetic
action, while the variable resistances produced thereby in the microphone in
reacting upon the telephonic coil produce intensified vibrations of the membrane,
causing buzzing sounds that are transmitted as Morse or similar signals to the
distant station substantially as decribed.
2. In a microphone signalling apparatus such as is referred to in the first claim,
the combination with the microphone apparatus of a telephonic apparatus by
means of a switch device so arranged that the telephone can be put in or out of
circuit with the microphone without interfering with the circuit of the latter,
substantally as described.
3. The combination of a microphone apparatus for signalling by buzzing sounds
and a telephonic apparatus, arranged and operating as herein described with
reference to the drawing.
Dated this 10th day of December 1898
ABEL & IMRAY,
Agents for the Applicants.