Patent GB-1138887-A (GB)
Title: Modular traffic signal controller
IPC: G08G1/07
Filed: 1966-11-28
Abstract: 1,138,887. Road traffic signalling apparatus. GENERAL SIGNAL CORP. 28 Nov., 1966 [21 Dec., 1965], No. 53083/66. Heading G4Q. A traffic signal controller is built of modular units so that functions can be added or removed by plugging in or removing a unit. The bottom unit is always a timer and power supply module (222, Figs. 1 and 2, not shown), and a threephase signal control module (which may be adapted for two-phase working) plugs into the top of the lowermost unit. If timed three-phase operation is required the circuit is completed by the addition of a jumper plug module (212); if further phases are required an additional twophase signal control module may be inserted between the three-phase unit and the top jumper plug module (Fig. 2C, not shown); if the system is to be controlled by traffic a traffic control module (311, Fig. 2D, not shown) is added below the jumper plug module. The individual modules may comprise printed circuit boards plug-coupled to a printed circuit mother board which is provided with bus-bars extending to plugs and sockets at the top and bottom which are adapted to mate with plugs and sockets of adjacent units. Time controlled system, Fig. 3A.-The various intervals in each phase are controlled by bistable circuits such as circuit 84 (labelled " walk ") which is the first interval in phase one. When this is energized it applies an enabling pulse on line 91 to the bi-stable 92 controlling the succeeding interval; it enables a triac to pass A.C. power from an input line k1 to the relevant signal lamp; and it applies a signal on line dl to a potentiometer (93, Fig. 3C, not shown) at the input of a timing unit (48, Fig. 3C) which produces an output on line y after the end of a period dependent on the setting of the potentiometer. This latter output energizes the next bi-stable 92 controlling the next interval (pedestrian clearance) when pulsating D.C. is supplied to a " DONT WALK" signal. This interval is similarly timed and then energizes the vehicle green period, followed by the vehicle clearance (amber) and the all-red periods to complete phase one. This is followed by similar sequences for phases two and three controlled by similar units in Fig. 3B (not shown). Parts of the cycle are completed by jumper connections normally short-circuited by the jumper plug module; if the latter is replaced by a further module the cycle is extended to include further phases or to include traffic-controlled intervals according to the nature of the further module. The circuit shown in Fig. 3A includes means for eliminating the walk and pedestrian clearance intervals if there is no demand. When the pedestrian push-buttons have not been operated, no signal is stored in the memory unit 33 which therefore provides an output on line n1 which is connected to a " Fast Step " bus connection (Fig. 3C, not shown) coupled to the timer unit (48) which gives immediate outputs on line y when the pedestrian intervals should operate, thereby stepping the cycle on to the initial green phase. Vehicle-controlled operation, Fig. 4A.-The addition of the vehicle-control module, Figs. 4A-4C, interrupts the cycle described above after each initial green period to provide a dwell period where the cycle stops until there is a demand for right of way on another phase. If the dwell occurs on phase one, the bi-stable 310 is operated and passes an enabling pulse to the bi-stable 312 controlling the next interval (timed extension). Vehicle demands from detectors VR1-VR3 are stored in respective storage units, such as 314, and if a demand occurs on phase two or phase three an input on line a2 or b2 passes through OR gate 322 to actuate the bi-stable 312 and start the extension period which maintains right of way on phase one until the gap between vehicles on this route is long enough for an interval timer 330 to time out or until a maximum timer 331 times out. If there is a demand on phase three but not on phase two, an arrangement similar to that described above for omitting the pedestrian periods allows the cycle to proceed from phase one to phase three.