Improvements in and relating to Telephonic Apparatus.
Year: 1887

page_text: Improvements in and relating to Telephonic Apparatus.
A communication from abroad by L. M. ERICSSON, of Stockholm, Sweden,
Electrician..
I, CHARLES BELL, of 29 Waterloo Street, Glasgow, Lanarkshire, Merchant, do
hereby declare the nature of this invention and in what manner the same is to be
performed to be particularly described and ascertained in and by the following state-
ment in writing, reference being had to the accompanying Sheet of Drawings:
This Invention has reference to new or improved arrangements of telephonic
apparatus, and especially of the local circuits in the apparatus, by which the dis-
connections and consequent disuse of the instrument which hitherto have often taken
place may be avoided; and comprises a new shunt connection, so that if the contacts
of the hook lever should become inoperative, the current can nevertheless pass through
a working circuit, and when the contacts are in working order one or other part of
the instrument is shut out by the current passing through a path in the circuit of less
resistance.
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And in order that this invention and the manner of performing or carrying the same
into effect or practice may be properly understood there is hereunto appended an
explanatory Sheet of Diagram Drawings, in which the same reference letters are used
to indicate as far as possible corresponding parts in both Figures where shown.
Figure 1 represents a Diagram view of the new or improved arrangement of telephonic
apparatus, and Figure 2 a corresponding view of the arrangement of apparatus at
present generally in use, so that the difference or distinguishing features of the two
systems may be more clearly observed.
Referring to the reference letters on both Figures of these Diagrams, L is the
connecting screw for the line-wire, and I for the earth-wire, A is the hand-telephone
receiving transmitter, B B¹ the electro-magnet and the armature of the signal-apparatus,
C the hook lever for the hand telephone A, D and E the two electric contacts of this
hook lever, (shown reversed in the now arrangement Figure 1). The Diagram
Drawings show distinctly the electric connections. When the hand telephone A is
hung on the end of the hook lever C and consequently pressing it down, in the system

page_text: at present in use and shown in Figure 2, the current runs from the line connection
at L, through the hook lever C, the hook contact D, and the electromagnet B B', to
the earth, when the signal-apparatus is connected and rings, but the hand telephone A
is shut out of the circuit. If the hand telephone A is taken off, a spring lifts the
hook lever C pressing it against the contact E, and the current runs from L through
C, E, A, to the earth I. If, however, dust or anything else should cause either of the
contacts D or E not to work, one part or other of the instrument would also become
inoperative and consequently it could not be used. Figure 1 shows the new or
improved arrangement in which corresponding parts are marked with the same letters.
It can be easily seen from the Diagrams without explanation how the current runs in
each case, also that the difference between the two arrangements is that in the new
system there is a shunt circuit besides the two Contacts D and E. If one of these
contacts should get out of order, the instrument is nevertheless able to work. Thus
it will be seen that if the hand telephone A is hung on its hook lever C, and the
contact E should not work to allow the current to pass from L through E, C, C¹ to
the electromagnet B, B¹, and earth I, the current can go from L through A, C" and
B, B', to the earth I. If the hand-telephone A is taken off the hook lever C, and the
spring contact D, does not work to permit the current to pass from L through A, C, D,
and B to I, the current can go in a similar manner from L through A, C, and B, B¹,
to the earth I. The only difference is that when the contacts E or D do not work,
the current has to pass through the circuit L, A, C, B, I, of greater resistance which
however does not keep the instrument from working through the Contacts E and D
when they are in proper contact working order, and are the circuit of least resistance.
Alterations may be made in the details of this arrangement without departing from
the main feature of the Invention, which is the formation of a shunt circuit independent
of the contacts D and E when these will not work.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I declare that what I claim is :-
In a telephonic apparatus or instrument, the forming of a shunt connection or
circuit, so that should the hook lever contacts D and E, become inoperative the current
can nevertheless pass through a circuit of greater resistance from the line connection
to earth, and when the hook contacts are in working order the current passes through
the circuit connection of least resistance, all substantially as herein described, in
reference to and shown in Figure 1 of the accompanying Diagrams.
Dated this 5th day of October 1887