Patent GB-807814-A (GB)
Title: Electric coded signal transmission systems
IPC: H04L25/42
Filed: 1957-04-25
Abstract: 807,814. Electric selective signalling. BENDIX AVIATION CORPORATION. April 25, 1957 [May 10, 1956], No. 13256/57. Class 40 (1). Data is transmitted in groups in the form of sets of discrete electric signals which are transmitted serially over a line and stored at the receiver end, all the signals being simultaneously read out of store in parallel form on receipt of an end-of-group signal, transmitted at the end of each data group. The transmitter consists of a commutator 2, Fig. 1, having a motordriven brush 4 co-operating with contacts 6, 8, S1-S4, 10, S5-S8 and 12 in sequence. Contacts S1-S4 and S5-S8 are connected to groups of terminals 22 and 24 respectively, voltages being applied to these terminals to set up code " words " A and B representing the data for transmission. The binary code may be used, a voltage on a terminal representing a " 1 " and the absence of a voltage, " 0." The other contacts 6, 8, 10 and 12 are permanently connected to battery 13. The first two are used to provide synchronizing pulses to synchronize the transmitter and receiver, and the second two provide end-of-group signals. At the receiver is a similar commutator device 32 having a rotatable brush 30 coupled by friction clutch 36 to constantly running motor. Normally the brush 30 is held by a latch 38 which is released upon energization of a solenoid 40 through relay contacts 48. Brush 30 initially rests on a home contact 62 and when released moves over contacts S<SP>1</SP>1-S<SP>1</SP>4, 64, S<SP>1</SP>5-S<SP>1</SP>8 and 66. Contacts S<SP>1</SP>1-S<SP>1</SP>4 are connected through delay circuits 68, 70, 72, 74 and contacts of relay 76 to output terminals 78. Relay 76 is operated when the brush reaches contact 64. Contacts S<SP>1</SP>5-S<SP>1</SP>8 are likewise connected through delay circuits 80, 82, 84, 86 contacts of relay 88 to output terminals 90. Relay 88 is operated when the brush reaches contact 66. Operation.-Two four-digit words A, B are applied to terminals 22, 24 and contacts 18 closed to initiate a revolution of the brush 4 by motor 14. Brush 4 first engages energized contact 6 which, being longer than the other contacts, generates a longer pulse as shown at 100 in Fig. 2. Next the brush'engages contact 8 to produce a " start " pulse 102. The next four segments contain the code word A forming a combination of pulses 104. Pulse 106 is formed by the contact 10, group 108 by code word B on contacts S5-S8 and pulse 110 by contact 12. The pulse 100 passes through the receiver brush 30 to the contact 62 and through normally closed contacts 44 to the relay 56. This is a slow-to-operate relay which will only respond to a pulse of sufficient duration. When it does respond it causes momentary opening of contacts 60 and closing of contacts 58. These respectively prevent momentarily energization of relay 42 and cause energization of relay 50. Relay 50 closes hold contacts 52 and contacts 54 which prepare a circuit to receive the start pulse 102 which then passes through contact 62, contacts 54 and 60 (now closed again) to energize relay 42. This relay opens contacts 44 and 46 to break the circuits to the other relays and closes contacts 48 to allow energization of coil 40 which releases the brush 30 to revolve at the same speed as brush 4 in the transmitter. The contacts S1-S4 are therefore connected individually to the contacts S<SP>1</SP>1-S<SP>1</SP>4 and the code word A applied to the delay circuits 68, 70, 72, 74. The delays are differentially adjusted so that, when relay 76 is operated by the brush 30 reaching contact 64 and transmitting the word completion pulse 106 to it, the code word A appears on the parallel output terminals. Code word B is likewise transmitted to the terminals 90 when relay 88 is energized by end-ofword pulse 110. Absence of the end-of-word pulse prevents the word being applied to the output terminals. The contact segments in the commutator 32 are longer than those in commutator 2 so that the transmitted pulses are not broken by brush 30 which is thereby protected from excessive wear.