Patent GB-1332934-A (GB)
Title: Navigation aiding apparatus
IPC: G08G1/00
Filed: 1970-11-27
Abstract: 1332934 Radio signalling MARCONI CO Ltd 27 Nov 1970 [18 March 1970] 12948/70 Heading H4L [Also in Divisions G4-G6] A navigation aiding appliance for road vehicles, comprises a box 1 having transparent windows 2 and 3 and through which a route card 6 is movable in steps so as to display the number of the road being followed in one window and the number of the road to be followed in the other window. In Figs. 1 and 3, the route card 6 is moved upwardly in steps by the driver pressing a spring-urged button 9 as he observes a road junction at which a change of road is required. The button 9 carries a triangular abutment 10 engaging holes 8 in the card 6, and a triangular abutment 14 is fixed to the body 1. The card 6 may be arranged to move downwards by reversal of the abutments 10 and 14, so that the lower window shows the road being followed. The box 1 may be attached to a metal dashboard by means of a magnet. In order to indicate automatically when a road junction is being approached at which a change of road is required, radio transmitters are provided at selected road junctions to transmit codes identifying each road at each of the junctions, and receiving means are carried by each vehicle in the system to receive the codes. The route card 6 is punched with digital codes representing the road numbers displayed in the windows 2 and 3. A punched-card reader (comprising metal fingers) reads the codes from. the card at each step and these are compared with the codes received from the transmitter. If the comparison identifies the approaching road junction as that at which the new road (shown in window 3) is to be adopted, a warning device, e.g. a light or buzzer, is activated. A reassurance indicator provides an aural or visual signal to the driver if the vehicle passes a road junction transmitter at which no change of road is required and if the correct road is being followed. The reassurance indicator is manually re-set. An alarm may be controlled by the non- operation of the reassurance indicator despite the reception of codes from a transmitter. A repeater transmitter may be provided a short way from each junction to provide further reassurance. Each transmitter (Fig. 6) comprises a shift register 15 programmed to provide an output signal consisting of a synchronizing pulse followed by the road codes (for the junction) separated by separation pulses. A free-running multivibrator 16 in one state supplies a clocking signal to a coincidence detector 19 and to the shift register 15. The multivibrator 16 in its other state provides a signal to an AND gate 21 which also receives the output signal of the shift register 15. The AND gate 21 is connected to the input of the coincidence detector 19 which itself is connected to a bi-stable device 27 controlling a modulator 28 keying a carrier wave source 29. The carrier wave is keyed ON if it is OFF, and OFF if it is ON, on simultaneous receipt by the detector 19 of a time marker pulse from the multivibrator 16 and a pulse from the AND gate 21. Each receiver (Fig. 7) comprises a demodulator and differentiator 30 which supplies pulses to an AND gate 34 and trigger a monostable device 32 having a mark time between ¢ and 1 that of the transmitter mark time. If a second pulse is received by the device 32 within its mark time, the device 32 is re-set and the pulse passes through AND gate 34 to the shift register 36, which thus receives the codes stored in the register 15 of the transmitter. Warning device (Fig. 8).-The codes received in the register 36 are applied via terminal 39 to shift registers 44 and 45 (one for each road) connected to coincidence detectors 46 and 48 to which are also applied via terminals 47 the codes read out by the reader from the punched route card 6. The code separation signals are applied to terminal 40 and the synchronizing signals are applied to terminal 41. A synchronizing pulse arriving at terminal 41 sets bi-stable devices 55 and 57 to give no signal to AND gate 60. Then if coincidence of codes is detected by the detectors 46 and 48 and a separating pulse appears on terminal 40, AND gates 51 and 53 open to switch the bi-stable devices 55 and 57 to their other states so opening AND gate 60 to switch bi-stable device 62 to activate a warning device 63 which remains activated until reset by the driver by means of a button 64 linked to the button 9. Reassurance indicator 66 (Fig. 8) is activated by the switching of a mono-stable circuit 65 (with timed reset) or a bi-stable circuit (with manual reset).