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Depth charge A time delay depth charge having a water actuated switch, an adjustable tr, and a firing circuit. The switch is actuated by submersion and operates to enable the timer: the timer triggers the firing circuit after a pre-selected period of time; and the firing circuit, thus triggered, provides an electrical output pulse for detonating the explosive charge.
Attorney, Agent or Firm: What is claimed is: 1. A depth charge having a time delay, wherein the charge is not enabled until submerged in a solution, and not detonable for a predetermined time thereafter, comprising: a power source; circuit means for providing the electrical output of said charge; timing means coupled to said circuit means for preventing said circuit means from providing said charge output for a predetermined period of time after said timing means is enabled; switching means for coupling said timing means to said power source and enabling said timing means when said switching means is submerged in said solution; selecting means included in said timing means for selecting one of a plurality of available time delays in providing said charge output after said timing means is enabled; a storage capacitor and a unijunction transistor also included in said timing means wherein the first terminal of said storage capacitor is coupled to a first terminal of said unijunction transistor and their junction is coupled to said selecting means, the second terminals of said capacitor and said unijunction transistor are coupled to said switching means, and the third terminal of said unijunction transistor is coupled to said circuit means. 2. The charge of claim 1 wherein said switching means is a water actuated switch including a transistor and a first switch wherein said transistor is non-conductive until said first switch is submerged in an electrically conductive solution. 3. The charge of claim 1 wherein said selecting means is a second switch having a plurality of terminals, each connected to a resistor, wherein each resistor differs in resistance from each other resistor. 4. The charge of claim 3 wherein each of the plurality of said resistors of said selecting means has one terminal coupled to an electrical junction common to all of said resistors and said common junction is coupled to the junction of said capacitor and unijunction transistor. 5. The charge of claim 4 wherein said circuit means includes a silicon controlled rectifier wherein its cathode terminal is coupled to said capacitor, its gate terminal is coupled to said third terminal of said unijunction transistor, and its anode is coupled to the charge output terminal. BACKGROUND OF THE INVENTION One of the most serious threats to water craft today is enemy swimmers. Attempts have been made on a large scale to both detect and destroy them. To this date there exists no way to reliably detect an enemy swimmer, nor to effectively destroy him. Previously, ineffective hand grenades and anti-personnel depth charges were deployed when enemy swimmers were suspected. Since hand grenades have a kill radius of approximately six feet they present little or no threat to a determined diver. Although previous depth charges are a considerable improvement over hand grenades, they have the disadvantage of detonating at a single depth only and, additionally, will not detonate in water shallower than that depth. The present invention overcomes the disadvantages of the prior devices. SUMMARY OF THE INVENTION The present invention is a depth charge having a detonation time selectible from a plurality of time delays. Since the depth charge will fall through water at a known rate, the depth at which the charge will detonate is determined by the time delay selected. As a safety feature the charge is disabled by a water actuated switch until submerged. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of the present invention; and FIG. 2 is a schematic diagram of the preferred embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT The block diagram of the present invention is shown in FIG. 1. The present invention comprises power source 10, water actuated switch 14, adjustable timer 16, and firing circuit 18 which provides output 20. Power source 10 is coupled to water actuated switch 14 which is, inturn, coupled to adjustable timer 16. Firing circuit 18 is coupled to and controlled by adjustable timer 16. FIG. 2 shows the present invention in schematic form wherein the numerical designations of FIG. 1 are retained to indicate the component composition of the respective blocks. Power source 10 is a battery or, more preferably, an activated thermo type battery. Such preferred batteries can supply no power until the electrolyte is released into the plates, which release can be controlled by the operator. Therefore, the preferred battery includes a safety feature which prevents the capacitive components of the circuit from becoming electrically charged. Fuse 12 is included in the circuit to prevent damage to the components resulting from an excessive current. Water actuated switch 14 includes switch 22, resistors 24 and 26 functioning as a voltage divider, voltage regulator diode 28, transistor 30, and resistor 44. When not submerged in water, switch 22 is highly resistive to electrical current. But, when submerged, it approximates a short circuit. If switch 22 is submerged, transistor 30 is conductive providing a low resistive path to ground for adjustable timer 16. Adjustable timer 16 is a unijunction relaxation oscillator which includes selectable resistance switch 32, capacitor 48, unijunction transistor 50, and resistors 46, 52, and 56. Switch 32 consists of a moveable arm for selectively coupling one of resistors 34, 36, 38, 40, or terminal 42 to power source 10. The magnitude of resistor 34 is greater than that of resistor 36, which is greater than that of resistor 38, which is in turn, greater than that of resistor 40. Switch 32 in combination with resistor 46 and capacitor 48 provide an electrical time delay, which delay is determined by the resistive value selected from resistors 34-40. By selecting the resistor and, therefore, the time delay, the depth for detonation is determined. When the voltage on capacitor 48 becomes greater than a certain percentage of that at terminal 54 of unijunction transistor 50, the diode becomes conductive, triggering firing circuit 18. As a safety feature, power source 10 may be shorted by selecting sterilization terminal 42 of switch 32, thereby disabling the circuit. Firing circuit 18 comprises silicon controlled rectifier 62, safety switch 66, and resistors 58 and 64. When transistor 50 is conductive a voltage appears at the junction of resistors 56 and 58. The voltage is applied through resistor 58 to gate 60 of silicon controlled rectifier 62, which enables the rectifier to apply the detonation voltage to output 20. As a safety feature, safety switch 66 may be closed to short the output, preventing detonation. A disarm button may be coupled to switches 32 and 66 such that, upon actuation, switch 66 will be closed and the arm of switch 32 will simultaneously be moved to terminal 42. The following list of components is offered by way of example only to show one of the operative embodiments of the present invention. NUMERAL COMPONENTS TYPE OR VALUE ______________________________________ 10 Activated thermal 30 volts type battery 12 Fuse 1/10 amp 24 Resistor 20 kilohm 26 Resistor 3 kilohm 28 Zener diode 1 N4747 30 Transistor 2 N3904 44 Resistor 2 kilohm 48 Capacitor 300 microfarad 50 Unifunction transistor 2 N1671 52 Resistor 300 ohm 56 Resistor 51 ohm 58 Resistor 1 kilohm 62 Silicon controlled 2 N2323 rectifier 64 Resistor 1 kilohm ______________________________________ The operation of the preferred embodiment of the present invention is as follows: Switch 66 is opened and the arm of switch 32 is moved from terminal 42 to the selected depth setting. Power source 10 is activated. Now the charge is operational. When submerged, switch 22 becomes a low resistive path, causing transistor 30 to become conductive. Transistor 30 operates to couple adjustable timer 16 and firing circuit 18 to power source 10. Capacitor 48 begins charging, the selected detonation and time delay being equal to the period of time required for the voltage on capacitor 48 to become greater than that at terminal 54. When the voltage on capacitor 48 is greater, unijunction transistor 50 becomes conductive enabling silicon controlled rectifier 62. SC R 62 then provides the detonation charge on capacitor 48 to output 20. If the charge is thrown into water shallower than the selected depth, it will detonate at the time the charge would have sank to that depth had the water been deeper. For U.S. patent law, rules, and procedures see MPEP. Disclaimer. Information presented on this page while believed to be reliable, is provided "as is" with no warranties of its accuracy or timeliness. For legal advice seek help of a licensed professional. |