IMPROVEMENTS IN MICRO-TRANSMITTERS.
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by the said William Johnson at the
Office of the Commissioners of Patents on the 22nd December 1880.
WILLIAM JOHNSON, of Sheffield, in the County of York. " IMPROVEMENTS IN
MICRO-TRANSMITTERS.'
My Invention, which has for its object improvements in micro-transmitters,
consists in a novel arrangement of the well known principle of the microphone of
Professor Hughes, together with resistance coils or shunts, all of which are
embraced in an electric circuit, and by which means I am able to render articulate
speech in the receiving telephone loud, clear, and distinct, the telephone being
attached to the line wire or conductor in the usual way.
In carrying out my Invention I arrange a microphone, which may consist of one
or two carbon pencils, on a diaphragm of wood, horn, mica, or other suitable
material, and between the ends of the carbon pencils I connect bobbins of insulated
wire in such a manner as to cause them to resist the passage of an electrical
impulse, or to act as a means of shunting such an impulse. I now couple up this
apparatus in a suitable manner, and provide several available paths for an electrical
current from a voltaic or other suitable battery.
The objects of my Invention which are attained by the use of the before
described arrangements are,-
Firstly. Great clearness of articulation in the receiving telephone, transmitted
speech being rendered with precision and force.
Secondly. The removal of the objectionable effects of extra vibrations of the
carbon pencils so prevalent in other instruments used as transmitters.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William Johnson in the Great Seal Patent Office on the
20th June 1881.
WILLIAM JOHNSON, of Sheffield, in the County of York.
MICRO-TRANSMITTERS."
"IMPROVEMENTS IN
My Invention relates to improvements in micro-transmitters, and it consists in
a novel arrangement of the well known principle of the microphone of Professor
Hughes, and also in a combination of such novel arrangement of a resistance coil
or coils, shunt or shunts, all of which are embraced in an electric circuit, the object
of my improvements being to render articulate speech and other similar sounds
loud, clear, and distinct in the receiving telephone, which is attached to the line
wire in the usual way.
In carrying out my Invention I arrange a microphone, consisting of two carbon
pencils, suitably supported on a diaphragm of wood, horn, mica, or other suitable
material, and between the ends of the carbon pencils I connect bobbins of insulated
wire in such a manner as to cause them to resist the passage of an electrical
impulse, or to act as a means of shunting such an electrical impulse; I now couple
up this apparatus in a suitable manner, and I provide several available paths
for an electric current from a voltaic or other suitable battery.
And in order that my Invention may be more fully understood I will now refer
to the accompanying Sheet of Drawings, the same letters of reference indicating
corresponding parts in both the Figures.
Figure 1 represents a micro-transmitter of my improved construction.
Figure 2 represents the same apparatus with the additions of a resistance coil
or shunt; A and A¹ are pencils of carbon loosely supported in blocks of the same
material B, B', and B2; these blocks are secured to a diaphragm, by preference of
pinewood, and which is fastened to a suitable sounding box.
C is a shunt or branch circuit of proper resistance; D is an induction coil, the
secondary coil of which is placed in the line circuit in the usual way.
It is well known that if an iron rod be inserted in the centre of a helix through
which a battery current is flowing the rod is rendered magnetic, also that the
magnetised rod reacts on the helix, and that the force of the current is thus largely
increased; it is also well known that if the contact with the battery be broken in
such circuit an extra current is induced, and this induced extra current will leap
across the interval with an intense and brilliant spark. If a carbon microphone
be placed in circuit with the primary of an induction coil, and the contact be
interrupted at the carbon points, combustion of the carbon will take place together
with the transference of carbonaceous particles from one point to another. This
action quickly destroys the sensitiveness and efficiency of the microphone when
used as a part of a telephonic transmitter, and this destruction takes place more
quickly still if the contact point or points of the microphone are formed of
substances which are subject to oxidation.
When the diaphragm of a microphonic transmitter is agitated by the speaker
at the sending station or from other causes, the continuity of the primary circuit
of the induction coil D is liable to rupture, and this rupture is manifested in the
receiving telephone in grating and disagreeable sounds and indistinctness in the
transmission of conversation, other troublesome defects immediately follow in
the microphone owing to the combustion or oxidation of points of contact. I will
now describe the electrical connections.
The positive current from the battery F passes through the primary E of the
induction coil D to the central block B'; it then either divides between the arms

page_text: or takes the arm or pencil which offers the least resistance, being either A or A',
and completes the circuit through the connection G. If contact is momentarily
interrupted in the arm A, the arm A¹ allows the circuit to be completed, and vice
versa, and thus the possibility of a breakage in the primary circuit is to a great
extent obviated; but in order to render the manifestation in the receiving
telephone of such a breakage impossible I introduce the branch circuit C, so that
if breakage or other disturbance should occur in the microphone by which the
circuit cannot be completed through the microphone, the circuit is then made
through the shunt C, which is of low resistance, thus effectually bridging over the
fault and allowing the induced extra current to pass without the injury to the
contact points, as hereinbefore mentioned, and thus speech is much more faithfully
reproduced and with increased clearness and distinctness of articulation. To
ascertain the proper resistance of the branch circuit or shunt C, I find the highest
point of resistance of the microphone when mounted for use by means of a
Wheatstone bridge, and I make the resistance of the shunt a little lower.
Having now described and fully ascertained the nature of my Invention, and
the manner in which it may be used or carried into effect, I would observe in con-
clusion that the construction of a telephonic transmitter, made according to my
Invention may be varied in its details without departing from the principle of my
Invention; but what I consider to be novel and original, and therefore claim
as the Invention secured to me by the hereinbefore in part recited Letters
Patent is,―
First. The arrangement of a micro-transmitter consisting of two carbon pencils
for the purpose of obviating induced extra currents in a primary circuit, sub-
stantially as herein before described and illustrated.
Second. The combination in a telephonic transmitter of a microphone of any
description, and one or more resistance coils or shunts of proper resistance,
substantially as and for the purpose hereinbefore set forth, described, and
illustrated.
In witness whereof, I, the said William Johnson, have hereunto set my hand
and seal, this Sixteenth day of June, in the year of our Lord eighteen
hundred and eighty one.
WILLIAM JOHNSON. (L.S.)