Emergency vehicle proximity warning system

• US 4,794,394 A
• Filed: 09/08/1987
• Issued: 12/27/1988
• Est. Priority Date: 09/08/1987
• Status: Expired due to Term

• Current Assignee: Thomas L. Halstead
• Original Assignee: Thomas L. Halstead
• Inventors: Halstead, Thomas L.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US07/093,620
• Time in Patent Office: 476 Days
• Field of Search: 340/901-906, 455/1, 455/9, 455/227-229
• US Class Current: 340/902
• CPC Class Codes: G08G 1/087 Override of traffic control, e.g. by signal transmitted by an emergency vehicle

Abstract

An emergency vehicle proximity warning system is disclosed which includes a low power transmitter subsystem carried on board an emergency vehicle and a special purpose receiver subsystem carried on board a second vehicle. The transmitter issues a continuous stream of equally timed-spaced pulses. The receiver subsystem detects the reception or non-reception of the pulses and includes a retriggerable multivibrator having an output which assumes a first logic state when the pulses are not present and a second logic state when the pulses are present. A relay coil, which is energized only when the retriggerable multivibrator is in its second logic state, actuates a set of normally closed relay contacts which are connected into the speaker leads of the vehicle'"'"'s conventional radio to interrupt the connection between the conventional vehicle radio and its speaker system when the pulses from an emergency vehicle are sensed. To provide a very clear indication to the vehicle operator that the emergency vehicle is nearby, one or more lamps and one or more emergency-sound-issuing devices are alternately energized and deenergized so long as the retriggerable multivibrator is in its second logic state to provide a visual and sonic alarm indication. Preferably, an astable multivibrator is coupled to the retriggerable multivibrator such that it is enabled only when the retriggerable multivibrator is in the second logic state to obtain the information for driving the alarm indicators.

Claims

1. An emergency vehicle proximity warning system comprising:

(A) a transmitter subsystem carried on board an emergency vehicle, said transmitter subsystem comprising;

(1) an oscillator for establishing the carrier frequency of operation for the transmitter subsystem, which carrier lies above the broadcast band;

(2) a modulator issuing a continuous stream of equally time-spaced pulses having a repetition rate in excess of 1000 hz;

(3) a mixer for accepting and mixing signals from said oscillator and said modulator to develop an output signal of said equally time-spaced pulses carried on the oscillator frequency;

(4) an output stage for accepting and power amplifying said output signal, said output stage having a limited power output such that its effective radiation range does not exceed a predetermined maximum; and

(5) a transmitting antenna for radiating the amplified output signal issued by said output stage; and

(B) a receiver subsystem carried on board a second vehicle, which second vehicle also carries on board a conventional vehicle radio, said receiving system comprising;

(1) a receiving antenna;

(2) a tuned circuit coupled to said receiving antenna and tuned to the carrier frequency of said transmitter subsystem;

(3) a demodulator coupled to said tuned circuit for detecting the reception of the continuous stream of equally time-spaced pulses issued by said modulator;

(4) a retriggerable multivibrator coupled to said demodulator for accepting demodulated signals therefrom, said retriggerable multivibrator including timing components establishing a characteristic response of said retriggerable multivibrator such that;

(a) when said retriggerable multivibrator does not detect the presence of a continuous stream of equally time-spaced pulses having a repetition rate of at least 1000 hz, the output of said retriggerable multivibrator assumes a first logic stage; and

(b) when said retriggerable multivibrator does detect the presence of a continuous stream of equally time-spaced pulses having a repetition rate of at least 1000 hz, the output of said retriggerable multivibrator assumes a second logic state;

(5) switch means responsive to said second logic state to disable the conventional radio carried on board said second vehicle, said switch means comprising;

(a) a relay coil coulped to said retriggerable multivibrator and energized only when said retriggerable multivibrator is in said second logic state; and

(b) a set of normally-closed relay contacts actuated by energization of said relay ocil, said set of normally-closed contacts being connected into speaker leads of the conventional vehicle radio such that, when said relay coil is energized, said set of contacts is actuated and opens to interrupt the connection between the conventional vehicle radio and its speaker system;

(6) an astable multivibrator coupled to said retriggerable multivibrator and enabled only when said retriggerable multivibrator is in said second logic state, said astable multivibrator, when enabled, issuing a continuous string of square wave pulses representing alternating first and second logic levels; and

(7) sensory alerting means responsive to the output from said astable multivibrator being in said first logic state for issuing an alarm indication, said sensory alerting means comprising;

(a) at least one emergency-sound-emitting device, which at least one emergency-sound-emitting device is alternately turned on and off as the output from said astable multivibrator switches between said first and second logic levels; and

(b) at least one lamp, which at least one lamp alternately flashes on and off in unison with said emergency-sound-emitting device being turned on and off as the output from said astable multivibrator switches between said first and second logic levels.