Review of the First 8-Line Switchboard
On March 7, 1876, Alexander Graham Bell received a patent for the telephone. Three days later, he made the first ever telephone call to Thomas Watson. The first public demonstration of the telephone was made by Bell on May 10, 1876, at the American Academy of Arts and Sciences in Boston (US). This demo kicked off the race (slow at first) to connect subscriber's telephones. See Appendix A for a telephone milestone timeline from 1875-1877.
George Coy saw an opportunity and developed/built the first commercial switchboard in 1878. His company was named District Telephone Company of New Haven. Eight telephone lines were available each supporting 3 party-line ring codes. So 24 customers could have been connected and, apparently, Coy had 21 initial customers. See Endnote A.
In 1929 J.J. Carty, VP of AT&T, praised the book by Frederick Rhodes, "Beginnings of Telephony." He said, "This book will serve as an inspiration to thousands of telephone workers... and as a chronicle of the beginnings of a great art and of a remarkable phase of human accomplishment."
Rhodes 1929 book does a great service to the early days of the first telephones and switchboards. The section below is a coverage of Coy's groundbreaking switchboard. The material provides a rare detailed explanation of exactly how the switchboard operated. The text and figures are from Rhode's book.
​Figure A1 is a model of the New Haven switchboard of 1878 and Figure A2 is a circuit diagram showing all of the apparatus and the necessary connections for tracing the progress of a call originated by subscriber A on line 1, for subscriber B on line 4.
Fig A1, Model of first commercial switchboard, installed New Haven, Connecticut in 1878
Fig A2, Circuit Diagram of Coy's Switchboard
Referring to Figure A1, at the top of the board were eight binding posts to which the subscribers' lines were individually connected. Below these were the equivalent of two cord circuits, each consisting of a pair of metallic switch arms. Each of these arms was capable of being rotated about an axis so as to connect with any one of eight metal studs, equally spaced on the circumference of a circle. Each pair of switch arms were electrically connected together through the centers about which they could be rotated.
Each of the eight subscribers' lines was connected electrically to one of the metallic studs or buttons belonging to each switch arm. Below these switch arms were eight switches, also capable of rotation and each one centrally connected to one of the subscribers' lines. Theses switches were normally placed in a vertical position they made contact with a metallic stud. Each stud was connected to battery and ground through a line relay (Fig. A2 ), which controlled an annunciator operating in a local circuit. The annunciators are shown at the upper right-hand corner of the switchboard (Fig. A1).
Each of the eight switches referred to above could be rotated into contact with the continuous horizontal metal strip beneath, to which was connected one terminal of the operator's telephone, the other terminal being connected to earth by means of the binding post shown to the right of the right-hand end of the horizontal strip. The operator's telephone was used for talking and listening. At the bottom of the board were eight more metallic switches to all of which the signaling mechanism was permanently connected. These switches also were capable of being rotated, each into contact With a metallic stud placed above it. One subscriber's line was connected to each of these studs.
The signaling apparatus, shown beneath the annunciator case (Fig. A1), was Thomas A. Watson's "buzzer." It consisted of a large induction coil, and a flat steel spring, which the operator could cause to oscillate by the hand operation of a lever, thus making and breaking a battery circuit. This action sent a series of electrical impulses to the called line, causing the telephones on that line to "howl" violently.
At each subscriber's station was a single hand telephone, used both for talking and listening, and a push button for operating the central-office annunciator. The system employed grounded lines. A primary battery was used to operate the annunciators and the buzzer.
Referring to Figure A2, when none of the subscribers' lines was in use, the switch arms L-1, L--2, L-3, and L-4 were in the "off" position, as were the signaling switches C-1, C-2, etc. Switches K-1,K-2, etc., however, were all in contact with their metal studs, forming closed circuits front ground, through the subscribers' sets and lines, central-office line relays, battery, and ground.
Method Of Operation
Subscriber A, on line 1, desiring to talk to subscriber B, line 4, depressed his push button P-A, which momentarily opened the circuit through line relay R-1, causing its armature to and close a circuit through annunciator A-1, which released its shutter, notifying the operator that a subscriber on line 1 desired to originate a call. The operator then moved switch K-1 from its metal stud, opening the line relay circuit for line 1, and rotated it into contact with the metal strip beneath, which connected the operator's telephone, T-O, with the tele-phone, T-A, of subscriber A, over line 1, now grounded at each end.
Upon learning that subscriber A desired to talk with subscriber B, the operator moved switch K-l from the metal strip to its "'off" position, moved switch K-4 from its metal stud to its "Off" position, and switchC-4 into contact with its metal stud, thus connecting the signaling apparatus to line 4.
To operate the buzzer, the operator moved lever R from side to side, which caused flat steel spring S to oscillate rapidly. This was a primitive ringing generator. The interrupted direct current from battery B-3, passing through the primary winding of induction coil I, caused pulses of induced current to be sent out over the line when plunger P was operated, thus re-moving the shunt around the secondary winding of induction coil I. The induction coil would increase the B-3 voltage sufficiently to cause the subscriber telephone to "howl." The Watson bell had not been invented yet so the telephone ear/mouth piece was used as the call indicator.
Assuming that subscriber B's signaling code was three, the operator pressed P three times, while operating lever R, which sent three series of impulses over line 4.
The operator then moved switch C-4 to its “Off" position, connected switch K-4 to the listening strip, and waited for subscriber B to answer his telephone. When he answered, the operator, after notifying him that subscriber A desires to talk to him, moved switch K-4 to its "off" position and completed the talking circuit for the sub-scribers by rotating switch arm L-1 into contact with the metal stud for line 1 and switch arm into contact with the metal stud for line 4.
The operator ascertained when the subscribers had finished talking by connecting either switch K-1 or to the metal strip at intervals. When, upon listening in this manner, it was found that the conversation was finished, the operator moved switch arms L-1 and L-2 to their "Off" positions, and connected switches K-1 and K-4 to their metal studs, thus closing the line relay circuits for lines 1 and 4 and per-mitting the restoration by hand of the annunciator shutters for those lines.
Appendix A
Bell Telephone Milestone Timeline
The following timeline is mostly from https://www.gutenberg.org/
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1875
February 27—Written agreement between Bell, Sanders, and Hubbard forming “Bell Patent Association” to promote inventor’s work in telegraph field.
June 2—Bell completes the invention of the Telephone, electrically transmitting overtones for the first time and verifying his principle of the electrical transmission of speech at 109 Court Street, Boston.
June 3—First telephone instrument constructed by Watson according to Bell’s specifications.
September—Bell at Brantford begins writing specifications for a telephone patent.
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1876
February 14—Application for telephone patent filed with U. S. Patent Office, Washington, D. C.
March 7—U. S. Patent 174,465 issued to Bell, covering fundamental principles of the Electric Speaking Telephone.
March 10—First complete sentence transmitted by telephone by Bell to Watson, “Mr. Watson, come here; I want you.” Between two rooms at 5 Exeter Place, Boston.
May 10, 1876, live public demo at the American Academy of Arts and Sciences in Boston.
June 25—Bell exhibits his Telephone to the Judges of the Centennial Exhibition at Philadelphia, on which he is awarded the Exhibition’s medal.
August 10—Experimental one-way talk—8 miles, Brantford to Paris, Ontario.
September 1—Contract with Thomas A. Watson for one-half his time—the beginning of telephone research laboratories.
October 9—First experimental two-way telephone conversation between different towns—2 miles, between Boston and Cambridgeport, Mass.
November 26—Conversation over railroad telegraph wires—16 miles, Boston to Salem.
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1877
February 12—Bell’s first public lecture and demonstration of his new invention given before the Essex Institute in Salem, where he had lived and had done some of his experimenting.
April 4—First outdoor line for regular telephone use installed—Boston to Somerville.
May 17—Telephone lines first interconnected by means of an experimental switchboard at 342 Washington Street, Boston.
July 9—“Bell Telephone Co., Gardiner G. Hubbard, Trustee,” the first telephone organization, formed.
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Endnote A: Regarding the first switchboard, according to Edison, "Tivadar Puskas was the first person to suggest the idea of a telephone exchange." A prototype was built by the Bell Telephone Company in Boston in 1877 but George Coy was the first to make a commercial board.
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