Electronic toilet tank monitor utilizing a bistable latching solenoid control circuit

Abstract

A fluid control circuit system is capable of maintaining fluid within a fluid tank at a desired level using electronic sensors and control circuitry, where the control circuitry and actuators are configured for low power consumption, thus allowing operation to be powered by a self contained internal power supply. To provide appropriate fluid control, the system includes a fluid sensor indicating if fluid is at a predetermined level, control circuitry attached to the fluid sensor, a latching solenoid attached to the control circuitry and also attached to a fluid control valve, and an internal power supply to power all electrical components.

Description

This application claims the benefit of Provisional Application No. 60/892,359 filed Mar. 1, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic toilet tank monitor utilizing a bistable latching solenoid control circuit to operate solenoid actuated valves. More generally, the present invention relates to a control circuit for controlling bistable latching solenoids used to control actuated valves.

2. Discussion of the Related Art

Certain common flush toilets include a water tank positioned above a toilet bowl. The tank holds enough water so that when the water in the tank is released into the bowl fast enough, the water will activate a siphon in the drain line of the toilet. In addition to requiring a certain volume of water, it is critical that the water is released into the bowl within a relatively small time frame, generally about 3 seconds in order to activate the siphon to flush the water out of the toilet bowl and into the drain pipe. After flushing the water out of the toilet, it is necessary to again fill the tank with the same volume of water. Current tank level controls on toilets use mechanical means to achieve the desired amount of water in the tank.

The flush mechanisms include a handle on the exterior of the tank that is mechanically coupled to a chain, which is connected to a flush valve within the tank. When a user pushes on the handle, the chain is pulled, thereby lifting the flush valve. This moves the flush valve out of the way, revealing a drain hole that is generally about 2- to 3-inches (5.08- to 7.62-cm) in diameter. Uncovering the drain hole allows the water to enter the toilet bowl. In addition to the volume of water in the tank and the diameter of the drain hole, the height of the water in the tank impacts the speed with which the water is released from the tank into the toilet bowl.

In many toilets, the toilet bowl has been molded so that the water enters the rim, and some of it drains out through holes in the rim. A good portion of the water flows down to a larger hole at the bottom of the bowl. This hole is known as the siphon jet. It releases most of the water directly into the siphon tube. Because all of the water in the tank enters the bowl in about three seconds, it is enough to fill and activate the siphon effect, and all of the water and waste in the bowl is sucked out.

Once the tank has emptied, the flush valve is repositioned over the drain hole in the bottom of the tank, so the tank can be refilled with water. A refill mechanism is then used to refill the tank to a predetermined height so it is ready for the next flush. The refill mechanism includes a valve that turns the water on and off. In current toilets, the valve is controlled by a filler or ball float. When the water level in the tank is low, the filler float or ball float falls. The valve is thereby opened in order to refill the tank and the toilet bowl. As the water level in the tank rises, the filler float or ball float also rises. Once the water level has reached the desired height as determined by the buoyancy of the float, the valve is switched into the closed position. An overflow tube within the tank allows excess water in the tank to be drained into the bowl to prevent the tank from overflowing.

In alternative embodiments, level indicators are electromechanical devices that work in combination with some control circuits, systems, and the like. Naturally, these types of devices require electrical power to operate. However, the known mechanical design used for refill mechanisms (discussed above) does not require electrical connections at the toilet. As such, existing toilets are not equipped with a constant power source. Further, bathroom facilities do not presently include power source which would be convenient to the installed toilet (such as outlets in close proximity). In addition, electro-mechanical level indicators used in toilet tank refilling mechanisms must function even during power outages. Based on the foregoing, there is a need for a toilet tank water control system that does not require a constant external power supply.

Based on the high frequency of toilet use, there exists a need for a mechanically reliable toilet tank water control system that can be operated at low power consumption levels.

Solenoids are well known electromechanical devices used to convert electrical energy into mechanical energy and particularly into short stroke mechanical motion. As such, solenoids have long been employed to actuate valves in response to an electrical signal. Typical applications of these solenoid valves include controlling fluid flow, gas flow, and the like. Conventional (non-latching) solenoids require a continuous energized state to maintain actuation.

To decrease the power dissipated by the solenoid, and particularly in applications where the solenoid is to be retained in the actuated position for significant time periods, latching mechanisms can be used to hold the mechanical output of the solenoid in one position or the other without requiring continuous power to the solenoid. Self-latching solenoid actuated valves are known in the art. Despite advances in self-latching solenoid actuated valves, there continues to be a need for smaller, faster acting self-latching solenoid actuated valves with low power consumption.

Bistable actuators have been used to provide some reduction in power consumption. With the introduction of new actuator designs, there has been the introduction of new control circuitry. Some known circuits for controlling bistable actuators have been integrated into actuators intended to replace conventional solenoid actuators for controlling water flow. While these integrated latching actuators consume substantially less power in the actuated state than conventional solenoid actuators, input signals to the latching actuators must remain on at all times in order to keep the actuators in position. Maintaining the coil of the actuator in an energized state in order to maintain the actuator in a predetermined position increases overall power consumption. Accordingly, there exists a need for a bistable latching solenoid control circuit with minimal power requirements for actuating a water flow valve.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a refill mechanism that can reliably control water level in toilet tanks by controlling the inflow of water. Such a refill mechanism will receive with input signals provided by toilet tank level indicators appropriately positioned in the tank to signal when predetermined water levels exist. It is another object of the present invention to provide a toilet tank water control system that does not require a constant power supply. It is yet another object of the present invention to provide a mechanically reliable toilet tank water control system that can be operated at low power consumption levels. It is still another object of the present invention to provide smaller, faster acting self-latching solenoid actuated valves with low power consumption. It is also an object of the present invention to provide a bistable latching solenoid control circuit with minimal power requirements for actuating a water flow valve.

The present invention achieves many of the above-referenced advantages by utilizing a control system and control components which are specifically designed for power consumption concerns. More specifically, a bistable latching solenoid is utilized as the control for opening and closing a related water or fluid valve. By using a bistable latching solenoid, the valve can be opened and closed using small pulse signals from the control system. Most significantly, the control system is not required to continuously energize the solenoid, thus operating in a more energy efficient manner. In addition, the control circuitry is also specifically configured to conserve power and operate in an energy efficient manner.

In addition to the power concern outlined above, fluid level sensing is achieved in a relatively straightforward and efficient manner. In one embodiment, this includes the use of two probes exposed within the tank capable of differentiating between the existence of fluid versus the existence of air. As such, when fluid covers both probes, the resistance therebetween changes which is detectable by the control circuitry. Naturally, other alternative fluid sensors could be utilized.

These and other objects and advantages of the present invention are accomplished by the toilet tank electronic monitor and bistable latching solenoid control circuit in accordance with the present invention. The invention will be further described with reference to the following detailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of an overall fill tube assembly for the toilet tank electronic monitor in accordance with the present invention;

FIG. 2 is top perspective view of the overall fill tube assembly of FIG. 1 shown mounted in a toilet tank;

FIG. 3 is a perspective view of a wired printed circuit board assembly connected to a power supply in accordance with the present invention;

FIG. 4 is a perspective view of the printed circuit board assembly of FIG. 3 shown wired to a solenoid;

FIG. 5 is a perspective view of one embodiment of the printed circuit board in accordance with the present invention;

FIG. 6 is an illustration of one embodiment of the operation of a latching valve in accordance with the present invention;

FIG. 7 is a schematic block diagram of the bistable latching solenoid control circuit;

FIG. 8 is a schematic circuit diagram of the bistable latching solenoid control circuit of FIG. 7; and

FIGS. 9(a)-(c) are timing diagrams of power preconditioning based on the various input signals.

DETAILED DESCRIPTION

A toilet tank electronic monitor 10 in accordance with the present invention senses the presence or absence of water, i.e. the water level, in a toilet tank 28 (FIG. 2) using detection pins. This detection methodology is thus used to control at least one flow valve via a control circuit. Referring to FIG. 1, the toilet tank electronic monitor 10 in accordance with the present invention includes a fill tube assembly 12, a valve 14, a solenoid 16 and a control box 18. Fill tube assembly 12 includes a water conduit 20, a water inlet end 22 and a valve inlet end 24. While water conduit 20 is depicted as a generally tubular shape in the figures, those skilled in the art can appreciate that water conduit 20 can have various shapes and sizes to accommodate water feed to valve 14. A water source is connected to water inlet end 22 such that water is supplied from water inlet end 22 through water conduit 20 into valve inlet end 24. Water is provided to fill nozzle 26 only when valve 14 is in the open position. Fill tube assembly 12 can be comprised of any water resilient materials, including but not limited to copper, polyvinyl chloride (PVC), and the like. The components of fill tube assembly 12 can be individual components that are operably connected to one another, one integrated assembly, or a combination of both.

Referring now to FIG. 2, the toilet tank electronic monitor 10 of the present invention is shown mounted in a toilet tank 28. A handle 30 on the exterior of tank 28 is connected to a flush valve 32 via a connecting means 34. Connecting means 34 can be a chain, a polymeric segment, a metal pole, or any such device that can be used to connect handle 30 to flush valve 32 while resisting corrosion and/or degradation due to being submerged in water. An overflow tube 36 is positioned within tank 28 such that tank fill nozzle 26 does not spray water directly into overflow tube 36. However, a portion of the water fill will be directed to the overflow tube 36 to provide toilet bowl sidewall rinse during the tank refill.

Referring now to FIG. 3, control box 18 is shown with a cover 38 removed to expose a power supply 40. Power supply 40 shown in FIG. 3 is a nine volt alkaline battery. Those skilled in the art can appreciate that various power supplies can be used, depending on the necessary requirements of the system. The present embodiment utilizes any power supply that provides at least 5 V DC, including but not limited to a plurality of 1.5 V batteries, a DC wall transformer, and the like.

Referring now to FIG. 4, control box 18 is again shown with cover 38 removed to expose a printed circuit board assembly (PCBA) 42 therein. PCBA 42 includes level indicators 44 and contains the necessary circuitry to carry out the control functions of the present invention. PCBA 42 is also wired to solenoid 16 in order to provide appropriate power signals based on input readings of water level from level indicators 44. In one embodiment, level indicators 44 utilize complimentary metal oxide silicon technology to sense the difference in resistance between air and water. This difference can then be used to establish a bistable input control for toggling solenoid 16. Those skilled in the art can appreciate that different types of level indicators, including but not limited to laser level indicators, sonic level indicators, and the like, can be used in accordance with the present invention.

FIG. 5 shows more detail of one embodiment of PCBA 42 in accordance with the present invention. The design and operation of this embodiment of PCBA 42 is discussed in greater detail below with regard to FIGS. 7-9. Those skilled in the art can appreciate that PCBA 42 can scaled up or down for use in various water flow valve and /or water level control applications.

Referring again to FIG. 1, in one embodiment, valve 14 is a magnetically latching solenoid valve. In this embodiment, valve 14 may have an internal diaphragm that can be hydraulically maintained in the open position. In another embodiment, valve 14 is a custom valve with similar operating characteristics.

Referring now to FIGS. 1 and 6, in one embodiment, solenoid 16 is 2/2 magnetically latching bistable solenoid having a coil resistance of 18±1 Ω and an operating voltage range of 6-12 V DC. Solenoid 16 in this embodiment can operate with latching valve 14 at a power down to 5 V DC and with a pulse width of 0.020 seconds (to close) and 0.060 seconds (to open). Operation under these parameters maximizes battery life for bistable latching solenoids. In position 1 46 on FIG. 6, if valve 14 is in the closed position and coil is supplied with voltage pulsed current 64 having a pulse width of 60 mS at inputs 60 and 62, valve 14 is placed in the open position where it remains until supplied with additional power. Supply of additional power is shown in Position 2 48 of FIG. 6. Here, when valve 14 is opened by supplying current as occurs in position 1, valve 14 can only be closed by again supplying pulsed current 66. Valve 14 remains in the closed or off position until additional power is supplied again. Further detail regarding this operation is outlined in relation to the control circuitry discussed below.

Those skilled in the art can appreciate that timing durations, solenoid driver devices, battery voltage, input control, and the like will be dependent upon application specific “latching solenoids” having unique operational requirements. Because various application specific “latching solenoids” can be used to control a variety of different types and sizes of flow valves, one embodiment of a bistable latching solenoid control circuit 50 in accordance with the present invention is discussed hereinafter without specifying particular timing durations, solenoid driver devices, battery voltage, input control, and the like.

Referring now to FIGS. 7 and 8, there is shown a schematic diagram 52 of bistable latching solenoid control circuit 50. The circled alphabetical references (A) through (L) are used as operational reference points referring to the application of power to circuit 50 and the power preconditioning that initializes operation of circuit 50. These circled alphabetical references also correspond to information in the circuit diagram of FIG. 8 and the timing diagram of FIGS. 9(a)-(c) as follows: “A” represents an input stage. “B” represents an input pulse delay. “C” represents a power preset. “D” represents a two input Schmitt Trigger NAND gate. “E” represents a positive edge triggered one shot pulse. “F” represents a positive edge triggered one shot pulse inverter. “G” represents a positive triggered one shot pulse delay. “H” represents a negative edge triggered one shot pulse. “I” represents a negative edge triggered one shot pulse inverter. “J” represents a negative edge triggered one shot pulse delay. “K” represents a latching solenoid line 1 for unlatch control. “L” represents a latching solenoid line 2 for latch control.

Referring in more detail to FIG. 7, schematic diagram 52 illustrates the existence of an input stage 70 which will receive a latched or unlatched signal at its input. Input stage 70 also receives power from battery 100 which has its output limited by a current limiting resister 102. An output from input stage 70 is then passed to an input pulse delay 72 which will feed one side of a two input Schmitt Trigger NAND gate 76. In addition, a power preset circuit 74 supplies a second input to Schmitt Trigger NAND gate 76 (in addition to any necessary power signals). The output from two input Schmitt Trigger NAND gate 76 is then provided to a pair of one shot pulse generators: negative edge triggered pulse generator 78 and positive edge triggered pulse generator 80. As will be recognized, each of these circuits will generate pulses at appropriate times in response to received falling or rising edges of pulses, received at the respective input. Connected to the output of negative edge triggered pulse generator 78 is an inverter 92 along with a pulse delay circuit 94. Inverter 92 feeds a high side MOSFET switch 98, while pulse delay circuit 94 feeds a low side MOSFET switch 96. Similarly, outputs from positive edge triggered one shot pulse generator 80 is provided to inverter 82 and pulse delay 84. Inverter 82 then feeds high side MOSFET switch 86 while pulse delay circuit 84 will feed a low side MOSFET switch 88. As discussed in greater detail below, each of these components cooperate with one another to provide appropriate control of latching solenoid 90.

Referring now to FIGS. 8 and 9(a)-(c), component references (R1, C1, U1, and the like) are used to identify certain components of circuit 50 which are configured to carry out the desired operation. Further, these references are also referring to the application of power to circuit 50 and the power preconditioning that initializes operation.

Circuit 50 depicted in FIGS. 7-9(a)-(c) is designed using complimentary metal oxide silicon (CMOS) technology for water level indication and Schmitt Trigger gating to obtain low frequency operation and low power consumption ideal for battery applications. Those skilled in the art can appreciate that various level indication and gating technology can be used when designing circuit 50 for various applications, including but not limited to control of substances other than water.

Circuit 50 performs one of two stable control operations based upon the input state “unlatch” or “latch” for latching style solenoids. Circuit 50 is powered by a single DC power source. When the DC power is applied to the circuit it will perform a solenoid “unlatch” operation as part of its power preconditioning initialization state. After the power preconditioning operation the circuit will respond to its input state. If the input state is “unlatch” then no further operation is performed. If the input state is “latch” then the circuit will perform the “latch” solenoid operation routine.

The “unlatch” and “latch” input control commands each initialize one fixed pulse to trigger the bistable latching solenoid. The input pulse is time delayed which limits how fast circuit 50 can toggle between the two input control states preventing both circuit paths from simultaneously actuating the solenoid operation. Bistable control of the latching solenoid requires bi-directional electrical current. In between a change of input states, circuit 50 will default to sleep mode for low power consumption.

Referring now to FIGS. 9(a)-(c) there is depicted a timing diagram which illustrates operation in accordance with the design of circuit 50 in the present invention. T1 through T9 along the top of the FIG. 9(a) are used to identify timing events. The timing events show the specific logic level states (“0” or “1”) for timing identifiers listed along the left side of FIGS. 9(a)-(c). These timing identifiers correlate with circled alphabetical references (A) through (L) and also correspond to like indicators on FIGS. 7 and 8.

Referring specifically to FIG. 9(a), there is shown a timing diagram for the application of power to circuit 50 and the power preconditioning that initializes operation of circuit 50 where the input state is set to “LATCH.” Timing Event T1 represents the application of DC power to circuit 50. As previously discussed, circuit 50 can be powered by a single DC power supply source (+V BATT). When power is applied to circuit 50, input bias voltage level (A) will begin to charge capacitor C2 through resistor R7 (B). Likewise, the applied power will begin to charge capacitor C3 through resistor R5 (C). In the power preconditioning stage, the input to U1C pin 9 will be at logic level “0” (C) until the capacitor C3 charge voltage exceeds the Logic Threshold Value (LTV) (Timing Event T5). Similarly, until the capacitor C2 charge voltage exceeds the LTV (Timing Event T6) the input to U1C pin 8 will be logic level “0” (B). As will be appreciated, U1C corresponds to the two input Schmitt Trigger NAND gate 76 as illustrated in FIG. 7.

With both inputs to U1C equal to logic level “0” the U1C pin 10 output (D) will be logic level “1” triggering the positive edge triggered “one shot” pulse (E). (Again, corresponding to pulse generator 80 shown in FIG. 7.) The positive edge triggered “one shot” pulse (E) will begin to charge capacitor C6 through resistor R12. The inverted positive edge triggered “one shot” pulse will bias the high side MOSFET Q3 into conduction (F). The pulse is inverted by UC2 (inverter 82) to provide this signal.

Timing Event T2 represents the beginning of the “UNLATCH” solenoid pulse. This is provided by an appropriate delay using pulse delay 84. Specifically, when capacitor C6 charge voltage exceeds the LTV of the U3A pin 1&2 input the delayed positive edge triggered “one shot” pulse (G) will bias the low side MOSFET Q4 into conduction initializing the latching solenoid “UNLATCHED” state (K).

Timing Event T3 represents the end of the “UNLATCH” solenoid pulse. When the positive edge triggered “one shot” pulse (E) completes the one pulse time period it will switch to logic level “0”. The inverted positive edge triggered “one shot” pulse (F) will bias the high side MOSFET Q3 into non-conduction de-energizing the solenoid (K) and causing a “free wheeling current,” or inductive kickback, from the inductive load of the solenoid.

Timing Event T4 represents dampening of the free wheeling current, or inductive kickback, from the solenoid. The positive triggered “one shot” pulse (E) logic “0” will begin to discharge capacitor C6 through resistor R12. When capacitor C6 discharge voltage drops below the LTV the delayed positive edge triggered “one shot” pulse (G) will bias the low side MOSFET Q4 into non-conduction and the unlatch cycle of the solenoid is complete. During the time period between T3 and T4 the MOSFET Q4 remains conductive allowing its internal “drain to source” protection zener diode to forward conduct the “free wheeling current” caused by the inductive load of the solenoid.

Timing Event T5 represents the end of power preconditioning. When the capacitor (C3) charge voltage exceeds the LTV (from Timing Event T1) the input to U1C pin 9 will be logic level “1” (C). As illustrated, Capacitor C3 and resister R5 correlate to power preset circuit 74. The circuit will remain in this state until further events are encountered.

Timing Event T6 represents operation of the solenoid with “LATCH” as the input command. This change will be in response to a change at the input, thus indicating that fluid is no longer present at the desired level. When the capacitor (C2) charge voltage exceeds the LTV (from Timing Event T1) the input to U1C pin 8 will be logic level “1” (B). With both inputs to U1C set to logic level “1” the U1C pin 10 output (D) will be logic level “0” and will trigger the negative edge triggered “one shot” pulse (H), which is generated by the components making up pulse generator 78. The negative edge triggered “one shot” pulse (H) will begin to charge capacitor C4 through resistor R6 of pulse delay 94. The inverted negative edge triggered “one shot” pulse (inverted by inverter 92) will bias the high side MOSFET Q1 into conduction (I).

Timing Event T7 represents the beginning of the “LATCH” solenoid pulse. When capacitor C4 charge voltage exceeds the LTV of the U1D pin 12&13 input delayed negative edge triggered “one shot” pulse (J) will bias the low side MOSFET Q2 into conduction initializing the latching solenoid “LATCHED” state (L).

Timing Event T8 represents the end of the “LATCH” solenoid pulse. When the negative edge triggered “one shot” pulse (H) completes the one pulse time period it will switch to logic “0”. The inverted negative edge triggered “one shot” pulse (I) will bias the high side MOSFET Q1 into non-conduction de-energizing the solenoid (L) and causing a “free wheeling current” (inductive kickback) from the inductive load of the solenoid.

Timing Event T9 represents dampening of the “free wheeling” current from the Solenoid. The negative edge triggered “one shot” pulse (H) logic level “0” will begin to discharge capacitor C4 through resistor R6. When capacitor C4 discharge voltage drops below the LTV the delayed negative edge triggered “one shot” pulse (J) will bias the low side MOSFET Q2 into non-conduction and the latch cycle of the solenoid is complete. During the time period between T8 and T9 the MOSFET Q2 remains conductive allowing its internal “drain to source” protection zener diode to forward conduct the “free wheeling current” caused by the inductive load of the solenoid.

Referring now to FIG. 9(b), there is shown a timing diagram for operation of circuit 50 when the input changes to the “UNLATCH” state. Referring now to FIG. 9(c), there is shown a timing diagram for operation of circuit 50 when the input changes again to the “LATCH” state.

While the invention has been described with reference to the specific embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments of the invention without departing from the true spirit and scope of the invention. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope of the invention as defined in the following claims and their equivalents.

Claims

1. A fluid level monitoring and control system for controlling the level of a fluid within a fluid tank, comprising:

a fluid level sensor positioned at a predetermined position within the fluid tank, the fluid level sensor having an output capable of producing an output signal indicative of the presence or absence of fluid;

a control circuit connected to the fluid level sensor output, the control circuit responsive the fluid sensor output signal to produce a first preset control signal when fluid is not detected by the fluid sensor and a second present control signal when fluid is detected by the fluid sensor;

an internal power supply for providing power to the control circuit; and

a bistable latching solenoid operably coupled to the control circuit to receive the first preset control signal and the second preset control signal, wherein the first preset control signal will cause the solenoid to be actuated to a first position and wherein the second preset control signal will cause the solenoid to be actuated to a second position.

2. The fluid level monitoring and control system of claim 1 wherein the solenoid is attached to a fluid valve such that actuation of the solenoid to the first position caused the fluid valve to be open, and wherein the actuation of the solenoid to the second position causes the fluid valve to be closed.

3. The fluid level monitoring and control system of claim 1 wherein the bistable latching solenoid has a first input and a second input, and wherein the first preset control signal is a predetermined pulse provided to the first input to cause the bistable latching solenoid to move to the first position, and wherein the second preset control signal is a predetermine pulse provided to the second input to cause the bistable latching solenoid to move to the second position.

4. The fluid level monitoring and control system of claim 1 wherein the bistable latching solenoid is a magnetically latching bistable solenoid.

5. The fluid level monitoring and control system of claim 1 wherein the fluid sensor comprises a pair of probes exposed to the fluid, wherein fluid level is detected by measuring the resistance between the pair of probes.

6. The fluid level monitoring and control system of claim 1 wherein the fluid sensor is a sonic level indicator capable of detecting the difference between air and fluid in close proximity thereto.

7. The fluid level monitoring and control system of claim 1 wherein the fluid sensor produces a state change at the fluid sensor output when fluid at the desired level is detected, and wherein that state change is detected by the control circuit to thus produce either the first preset control signal or the second present control signal.

8. The fluid level monitoring and control system of claim 1 wherein the fluid tank is a fill tank for a toilet.

9. The fluid level monitoring and control system of claim 1 wherein the fluid tank is a manufacturing process supply tank providing fluid to a manufacturing process.

10. The fluid level monitoring and control system of claim 1 wherein the internal power supply comprises a battery.

11. A toilet tank fluid level control system for maintaining fluid at a predetermined level, comprising:

a fluid sensor positioned at a predetermined level within the toilet tank to monitor the presence of liquid at the predetermined level;

a control circuit coupled to the fluid sensor for receiving a signal from the fluid sensor indicative of the presence or absence of fluid at the predetermined level;

a magnetically latching bistable solenoid coupled to the control circuit, the latching solenoid capable of being toggled between a first position and a second position, wherein the movement of the solenoid is responsive to a control signal produced by the control circuit;

an internal power supply operably coupled to the control circuit and the solenoid to provide operating power therefor; and

a control valve attached to a fluid line which provides fluid to the toilet tank when the valve is open, the control valve attached to the latching solenoid such that the valve is open when the solenoid is in the first position, and the valve is closed when the solenoid is in the second position.

12. A toilet tank fluid level control system of claim 11 wherein the fluid sensor comprises a first probe and a second probe exposable to fluid within the tank and wherein the control circuit is capable of detecting when both the first probe and the second probe are submerged in fluid.