Alarm

Abstract

A system for sounding an alarm when an unauthorized person or unidentified object enters a swimming pool. The system employs a float containing a battery powered transmitter tuned to a selected fixed frequency. The transmitter is energized when the person or object enters the water whereby a signal at said frequency is transmitted. A receiver tuned to the same signal acts as a monitor by receiving the signal and reproducing same in form suitable for sounding the alarm.

Description

SUMMARY OF THE INVENTION

My invention is a system for sounding an alarm when an unauthorized person or object enters a swimming pool, as for example when a child too young to swim falls accidentally into the water, whereby appropriate corrective action can be taken, for example, to prevent the child from drowning.

To this end, a radio transmitter is energized at the time the child falls in the water to transmit an alarm signal of fixed frequency. A receiver tuned to this frequency receives the signal so transmitted whereby an alarm can be sounded as for example by reproducing the signal as an audio wave in a loudspeaker.

The transmitter, which is battery powered, is disposed with its battery into a float resting in the water. The transmitter is connected to the battery via normally open switching means in the float which is closed when and only when a wave is produced in the water. In the absence of a wave, the transmitter is inoperative. When a wave is produced, for example by the child falling into the water, the means is turned on, actuating the transmitter which then produces the alarm signal as previously indicated.

The switching means can take the form of two electrical contacts disposed in spaced relationship on the surface of the float, one contact being disposed below the waterline, the other being disposed at a preselected level above the waterline. As soon as the water level ceases to be smooth whereby small waves are formed, the wave will break upon the float whereby both contacts are momentarily below the waterline. The water establishes an electrical connection between the contacts whereby the circuit is completed and the transmitter turned on. Additional means in the transmitter prevents the circuit, once completed, from being broken once the waves subside and the electrical connection between the contacts is broken.

The transmitter can employ a multivibrator of low repetition rate together with a high-frequency oscillator, both elements being operative in a time sharing mode, resulting in on-off transmission at an audio rate.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of my float; and

FIG. 2 is a circuit diagram of my invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, the following parts have the following numbers:

radio frequency oscillator transistor 1 audio frequency oscillator transistor 2 resonant load coil 3 radio frequency oscillator bias resistors 4, 5 and 6 audio frequency oscillator bias resistors 7 and 8 load resistors for modulation 9 and 10 radio frequency decoupling capacitor 11 radio frequency choke 12 bypass capacitor 13 coupling capacitors 14 and 15 resonant crystal 16 equivalent resistance or conductance path of water wave 17 switch contact above waterline 18 switch contact below waterline 19 silicon controlled rectifier 20 current limiting resistor 21 water 22 on-off switch 23 transmitter antenna 24 adjustment for contact 18 25 float 26 transmitter housing 27 battery 28 water wave 29 receiver 30 receiver antenna 31

The transmitter uses transistors 1 and 2 together with the interconnecting components to form a combination of a multivibrator having a low repetition rate and a high-frequency oscillator, both multivibrator and oscillator having a time sharing mode which results in on-off transmission at an audio repetition rate.

The audiofrequency transmitter section includes transistor 1, circuit 3, resistors 4, 5 and 6, crystal 16 and antenna 24. Transistor 1 provides the necessary amplification for sustained oscillations and radiation. Crystal 16 determines the frequency at which positive feedback and hence oscillation occurs. Coil 3 functions as a loading circuit at radiofrequency (the distributed capacitance causes the coil to be resonant at the desired radiofrequency), thus determining the conditions for developing oscillation, and also couples the signal to the antenna 24 for transmission.

Resistors 4, 5, 6 and 9 determine the direct current operating conditions of transistor 1, while resistors 7, 8 and 10 determine the direct current operating condition of transistor 2. Capacitor 11 has a value at which the radiofrequencies are bypassed without changing the audio repetition rate. Coil 12 has a value at which radiofrequency feedback to transistor 2 is inhibited, but audiofrequency feedback continues.

When oscillations occur, the output signal from transistor 2 is supplied as a positive feedback signal to transistor 1 via capacitor 15. Transistor 1 then oscillates at a radiofrequency determined by crystal 16. After a time interval determined primarily by resistors 5 and 6 and capacitor 15, transistor 1 is cut off and radiofrequency oscillations cease. At the same time, however, a signal developed across resistor 9 is fed back to transistor 2 via capacitor 14 whereby the multivibrator (audio rate) oscillations continue. The multivibrator, which operates as long as the transmitter in operation, first turns transistor 1 on and transistor 2 off, then reverses these conductive and nonconductive states, then again reverses these states and so on. Radiofrequency transmission occurs only when transistor 1 conducts. The net result is to produce a radiofrequency signal modulated or interrupted at an audio rate.

The transmitter is disposed in float 26. As long as the water level is essentially undisturbed and quiescent, contacts 18 and 19 are electrically isolated and no power is consumed. The transmitter is inoperative. When the water level is disturbed, as for example by a child falling into the water, wave 29 impinges upon the float and completes a circuit between the contacts 18 and 19. (The equivalent circuit is shown at 17. Water, even distilled water, is sufficiently conductive for this purpose.)

Rectifier 20 is normally nonconductive, but is switched into full conduction as soon as circuit 17 is established. Thereafter, rectifier 20 will remain conductive even after circuit 17 is broken so as to maintain the transmitter in operation. Resistor 21 limits current flow in the gate of rectifier 20. Once rectifier 20 is conductive, it can be turned off by momentarily interrupting power flow by manually opening switch 23.

Adjustment 25 permits the vertical separation between contacts 18 and 19 to be varied as necessary to prevent spurious alarms, as, for example, when pebbles are tossed in the pool. Adjustment 25 can form a protective cap over contact 18 which prevents rain from establishing conduction and activating the transmitter.

The signals transmitted via antenna 24 are intercepted by antenna 31 and reproduced in receiver 30 suitably tuned to the frequency of the transmitted signal.

It will be obvious to those skilled in the art that the same principles of my alarm system can be used in different environments by replacing contacts 18 and 19 by any other type of switching device responsive to a desired condition to actuate the transmitter.

Claims

What is claimed is:

1. Apparatus for transmitting an alarm signal in the form of an electromagnetic wave upon the occurrence of a selected condition, said apparatus comprising:

first switch means having first and second spaced contacts, said first means being normally open and being closed when said condition occurs;

a float supporting said first means and adapted to float on the surface of a body of water with one contact above the waterline and the other contact below the waterline, said condition being produced when waves of water are generated on said surface and both contacts are interconnected by a continuous liquid path;

a shield at said first means for preventing rain from establishing said path;

a transmitter in said float which, when actuated, produces said signal;

a power source in said float, said transmitter being actuated when coupled to said source;

second switch means in the float which is normally open and coupled to the first means, said second means being adapted to close when the first means is closed and, once closed, remaining closed until manually reset or until the source is drained of power; and

third means in the float connecting said first means, second means, source and transmitter to couple the source to the transmitter when the second means is closed.

2. Apparatus as set forth in claim 1 including fourth manually controlled means for varying the separation between said contacts.