Patent GB-1280146-A (GB)
Title: Traffic light control system
Inventor: HIGGINBOTTOM JOHN HAROLD
IPC: G08G1/07
Filed: 1968-09-27
Abstract: 1280146 Road traffic signals EIH ELECTRONICS Ltd 18 Dec 1969 [27 Sept 1968] 46132/68 Heading G4Q A system for controlling two sets of traffic lights LR, LA, LG and RR, RA, RG each having red, amber and green lights and intended as a portable system for road works, may operate automatically to change the lights in a continuous sequence or may be operated manually. The system comprises a magnetically-coupled multivibrator PG from which clock pulses are fed to a counter C through a gate circuit G1, the pulse repetition rate being variable between one and ten pulses per second to enable the RED ON time to be varied between 60 and 6 sees. and the GREEN ON time to be varied between 180 and 18 secs. The AMBER ON time remains constant at 3 sees. The counter C is an eight bit binary counter and is reset at or after a count of 240 by a multivibrator circuit CR. Gate circuits G3A, G3B, G3C, G3D connected to the counter C give outputs at counts 1, 60, 61, 240, respectively. Each signal lamp, e.g. LR, is individually controlled by an S.C.R. switching circuit, viz. S1L, having an ON input and an OFF input, the three switching circuits of each set of traffic lights, e.g. S1L, S2L, S3L, being controlled by a separate gate circuit, viz. G2L. Each gate circuit G2L, G2R comprises six logic circuits each consisting of two input AND gates, the gate circuits providing a "go-no-go" system controlling pulses fed to the switching circuits S1L, S2L, S3L, S1R, S2R, S3R. A gate changeover circuit SCO consisting of a bi-stable circuit determines which gate circuit G2L or G2R shall be operative at any one time and this in turn determines which traffic light set is operative. Delay circuits DL1, DL2 control the ON time of the amber lamps LA, RA and also prevent clock pulses from the generator PG being fed to the counter C whilst the amber lamps are lit. An oscillator O and gate G4 provide a safety system preventing the lighting if the two green lamps LG, RG or the two amber lamps LA, RA, at the same time. The gate G4 comprises AND gates and is controlled by the changeover circuit SCO so that a continuous train of pulses is directed to the "off" inputs of the green and amber switching circuits of that traffic light set which should not be operating. Automatic or manual operation is selected by switches S4A, S4B. Automatic operation.-A start button S2 is pressed to reset the counter C over line 1 and a cancelling voltage is applied over line 2 to the "off" inputs of the amber and green light switching circuits. On release of the button the counter C commences to count. At a count of one a pulse is fed from gate G3A over line 3 to circuit SCO and circuit PS5 and from the latter a pulse is fed over line 4 to circuits G2L, G2R. The output of circuit SCO is fed over lines 5, 6 to control the gate circuits G2L, G2R such that one circuit is activated and the other locked out. If, for example, circuit G2L is already activated, a pulse is fed to the "on" input of red lamp switching circuit S1L. Simultaneously, the circuit SCO locks out the circuit G2L and activates the circuit G2R so that the latter circuit now functions to sequence the lamps RR, RA, RG. Firstly, circuit G2R supplies a pulse to the "on" input of red lamp switching circuit S1R. At the count of sixty a pulse released by gate G3B is fed over line 8 to the delay circuit DL1 and over line 7 to pulse shaper PS2. Gate G2R is operated by the pulse from circuit PS2 and causes lighting of amber lamp RA. After three sees. circuit DL1 feeds a pulse over line 9 to shaper PS1 and the latter circuit supplies pulses to the inputs of circuit G2R whereby the circuit G2R feeds amber "off", red "off" and green "on" pulses to the switching circuits S1R, S2R, S3R so that the lamps RR, RA are switched off and the lamp RG is switched on. The counter C continues to count until 240 when gate G3D feeds a pulse over line 11 to delay circuit DL2 and over lines 12, 7 via shaper circuits PS4, PS2 to gate circuit G2R. The two output pulses of circuit G2R are fed to the green "off" and amber "on" inputs of switching circuits S3R, S2R so that the green lamp RG is switched off and the amber lamp RA on. After three sees. circuit DL2 feeds a pulse over line 13 to pulse shaper PS3 which produces pulses which are fed via gate circuit G2R to the "off" input of circuit S2R and the "on" input of circuit S3R to switch off the amber lamp RA and switch on the red lamp RR. The output from PS3 is also fed over line 14 to the circuit CR to reset counter C. Manual operation.-On pressing button S2 the cycle continues as for "Automatic" but stops when the green lamp is lit and remains in this condition until a switch S3 is opened whereupon the cycle continues to its completion and then continues until the green position is reached again. The switch S3 may be alternatively operated by a road vehicle.