Field of the Invention

This invention relates to door holders that automatically release a held-open door upon a predetermined event, such as the detection of smoke, and in particular, to such devices that are powered by a local power source such as a battery. Background of the Invention

Many releasable door hold-open devices are known in the art for automatically releasing a held-open door when a predetermined condition is detected, such as the existence of smoke or heat. These devices are often used with fire doors, which must be closed in the event of a fire to inhibit spreading of the fire.

Most prior devices employ a solenoid that must be continually energized to hold open the door. Representative examples of such devices are disclosed in representative U.S. Patent Nos. 3,729,771, 3,771,823, 3,905,063 and 4,040,143. When smoke or heat is detected, or if current to the device is interrupted, the solenoid is de-energized, thus automatically releasing the door and allowing it to close under the force of a door closer. This implementation has the distinct disadvantage of requiring the electric actuator to be continuously energized to hold the door in the open position. A continuously energized actuator draws a large continuous electrical current, which wastes electricity, decreases the life of the actuator and makes battery operation impractical. Other shortcomings of door hold-open devices employing remote power sources include the expense and complication of providing wiring to the devices and the necessity of resetting multiple devices after an alarm condition.

The method of wiring such prior devices presents additional problems. A continuous current requires wiring the door hold-open device to the main power supply of the building, which is expensive, particularly for older building which must be retrofitted. Since the electric actuators in many prior devices do not run off a typical 120 volt electrical supply, special transformers and wiring are required, again at additional cost. In addition, when multiple door hold open devices are wired to a

common fire or smoke alarm, the wire connections for different devices are often different. For example, the first, last and intermediate devices in a series of devices must often be wired differently. This causes confusion and frequently results in incorrect wire connections. Since prior hold-open devices are usually connected to a central electrical source, the devices are subject to damage from power surges caused by lightening strikes and power surges from the electric supply.

Another problem faced by prior hold open devices occurs when they are wired to a common smoke or fire detector. An alarm condition may result in the release of all doors wired to the system, even though many of those doors may not be near the fire or smoke.

Because prior hold-open devices typically employ a remote power source, doors will be released if a power failure occurs, even if no fire is present. After the power is restored, each unit having a smoke detector must be individually reset before it will hold the door open. This is an inconvenient and time-consuming task. Door hold-open devices that employ a local power source, such as a battery, can solve many of the foregoing problems. However, battery-powered door hold- open devices suffer from the shortcoming of having a short battery life. This is due to the constant current which must be used to monitor for an unlatch condition, as well as the larger current which must be used to actuate the motor or solenoid in the latching mechanism. Accordingly, it is desirable to provide a door holder with a means for minimizing power consumption during inactive periods.

Finally, many prior hold open devices can accommodate only one type of door-closer unit. This increases the cost of the unit because the purchaser must also pay for the closer unit. There is a felt need for a universal hold-open device that can be installed in conjunction with any type of preexisting door closer.

U.S. Patent Nos. 4,506,407 4,656,690 and 4,715,146, disclose automatically releasable hold-open devices that allow a door to latch open while the actuating device is not energized. However, these devices suffer from an even greater defect. Should the power supply to the device fail, a latched-open door will not be released. Most building codes require that door hold-open devices include a fail¬ safe feature to automatically release a door upon interruption of the power source. While a battery power supply is practical for this type of hold-open device, it is not safe because the battery may, without warning, become so discharged that it

cannot provide sufficient electromotive force to release the door. Thus, if the power fails before the device detects smoke or heat, the door will remain open allowing a fire to spread more rapidly. Objects of the Invention One object of the invention is to provide an automatically releasai-^ door hold-open device that does not require a continuous current be providec .^ the latching mechanism to hold-open a door.

Another object of the invention is to provide an automatically releasable door hold-open device that does not require special wiring to the building in which the device is installed.

Another object of the invention is to provide an automatically releasable door hold-open device that can be powered by a battery.

Another object of the invention is to provide an automatically releasable door hold open device having an integral smoke detector. Another object of the invention is to provide a door hold open device that will release a door when the battery's voltage drops below a predetermined threshold, or when the battery is removed.

Another object of the invention is to provide an automatically releasable door hold-open device that consumes a minimum amount of current. Another object of the invention is to provide a door hold-open device that will release a door when the battery's voltage drops below a predetermined threshold, or when the battery is removed.

Another object of the invention is to provide a door hold -open device that utilizes a servo motor actuated by a modulated signal. Another object of the invention is to provide a door hold-open device that utilizes a microprocessor and a microprocessor de-energization circuit.

Still other objects and advantages of the invention will become apparent to those of skill in the art after reading the following description of a preferred embodiment. Summary of the Invention

A door hold-open device which unlatches a held door based upon the occurrence of an unlatch condition includes a door latching mechanism and a signal processing circuit that provides power to the latching mechanism. The device conserves energy providing by withholding power from the signal processing

circuit until an unlatch condition occurs. The device further prevents a door from being latched in an open position if (a) the power to the system falls below a predetermined threshold, or (b) a battery access member is moved to permit disconnection of a battery. Brief Description of the Drawings

Fig. 1 is a top partial section showing one embodiment of the door hold open device of the present invention in a latched position.

Fig. 2 is a top partial section showing the door hold open device of Fig. 1 in an unlatched position. Fig. 3 is a section of the housing of the invention showing the position of the reciprocating member in the track of the housing.

Fig. 4 is a section of the housing of the invention showing the position of the hardware and motor mount in the track of the housing.

Fig. 5 is a circuit diagram of the door hold open device of Figs. 1 and 2. Fig. 6 is a side view of the battery access switch of the present invention.

Fig. 7 is a partial section of another embodiment of a battery access member of the present invention.

Fig. 8 is a top partial section showing a second embodiment of a door holder in a latched position in which a servo motor is used. Fig. 9 is a top partial section showing the door holder of Fig. 8 in an unlatched position.

Fig. 10 is a circuit diagram of the door holder of the embodiment of Figs. 8 and 9 of the invention.

Fig. 11 is a flowchart for the software of the microprocessor of the door holder.

Detailed Description

Referring to Fig. 1 , the device of the invention includes elongate housing generally designated as 11. Housing 11 includes track 12 along which reciprocating member 17 may slide. Reciprocating member 17 receives rod 14, and also translates the degree of the door's open or closed position to a point along the rectilinear path of track 12. It should be understood the preferred embodiment of the present invention is intended to be used with a door having a separate door closer (not shown) which continuously urges the door toward a

closed position. However, it is within the scope of the invention to integrate a door closer component within the housing used for the present hold open device.

The position of reciprocating member 17 within housing 11 may be further understood with reference to Fig. 3. Housing 11 contains two symmetrical tracks 151 and 152. Track 151 holds reciprocating member 17, through which bolt 153 passes. Bolt 153 holds guide washer 154, spacer 155 rod 14, all of which are held in place by nut 156. As shown in Fig. 4, track 152 is narrower than track 151, and receives base plate 50 at one end of housing 11, and circuit board 157 at the opposite end (see Fig. 1). Electrical wires 150 also traverse the interior housing, to connect circuit board 157 to motor 60 and magnetically operated reed switches 71 and 72.

Reciprocating member 17 has two resilient fingers whic . extend toward pivotable latch arms 30 and serve as latch arm receiving means. These fingers may comprise nylon or plastic, or any other material which is somewhat stiff yet resilient. The end of each finger contains an outward protrusion 26. The edge of each protrusion closest to the center of reciprocating member 17 is a convex arc with a radius of 1 /8 inch. The arc swings out from the outside of fingers 25. Tne tips of fingers 25 comprise 45° ramps 28.

As the door moves from a closed to an open position, rod 14 translates the door's movement to reciprocating member 17 which moves from the unlatched position shown in Fig. 2 to the latched position shown in Fig. 1. Fingers 25 are positioned to engage latch arms 30 and thereby keep reciprocating member 17 in a hold open position. The latching mechanism is operated by a DC motor 60 connected to a battery 100 through electronic circuity described in detail later. The latching means includes a pair of latch arms 30 pivotally mounted on base 50 by pins 32. Base 50 is formed from a single piece of sheet metal, and includes flanges 52 which extend upward and partially cover latch arms 30. Pins 32 each extend from flanges 52, through arms 30, and into base 50. The pivot point of each latch arm is such that when the latching mechanism is in the unlatched position, as shown in Fig. 2, the protrusions of arms 30 are separated by a distance greater than the width of fingers 25. The ends of latch arms 30 closest to reciprocating member 17 contain inward protrusions 35. Protrusions 35 are defined by a concave arc with a radius of 1/8 inch, and mate with the protrusions 26 of fingers 25. The inside of protrusions 35 include ramps at an angle of 45 degrees

from the outside of latch arms 30. The tips of latch arms 30 are rounded. The ends of latch arms 30 opposite the latching ends contain small inwardly-facing posterior protrusions 36.

A DC motor 60 is mounted on a flange 51 projecting perpendicular to base 50 and is secured thereto by screws 61. DC motor's rotating shaft 67 includes externally threaded rod 62 which extends between latch arms 30 equidistant from each arm. Cam 63 includes internal threads to receive threaded rod 62. By actuating DC motor 60, cam 63 is reciprocably inserted and withdrawn from between posterior protrusions 36 of latch arms 30. If DC motor 60 is energized to rotate shaft 67 in a counterclockwise direction, cam 63 will be driven away from motor 60, from the position shown in Fig. 2 to the position shown in Fig. 1. Tapered sides 65 of cam 63 will engage posterior protrusions 36, forcing them outward. As cam 63 advances, the latching end of latch arms 30 are forced inward around the fulcrum of the mounting pivot pins 32. When DC motor 60 is energized to rotate shaft 67 in a clockwise direction, cam 63 is withdrawn from between the posterior protrusions 36, allowing latch arms 30 to move freely.

With cam 63 fully inserted between posterior protrusions 36 as shown in Fig. 1 , a door may be latched open. This is accomplished by opening the door, thus forcing reciprocating member 17 toward motor 60, until fingers 25 reach latch arms 30. At that point, a slight additional opening force must be applied to the door to force resilient fingers 25 toward each other and between latch arms 30. Once the protrusions 26 on resilient fingers 25 have passed protrusions 35 of latch arms 30, reciprocating member 17 will be latched as shown in Fig. 1. This results in holding the door open until cam 63 is withdrawn, allowing latch arms 30 to pivot freely. At this point, the bias of door closer (not shown) will begin to close the door, moving reciprocating member 17 away from motor 60. This motion will cause fingers 25 to push latch arms 30 outward, unlatching reciprocating member 17.

Even when the hold open device is in its latched position as shown in Fig. 1, the door may be closed by manually applying a closing force to the door sufficient to cause resilient fingers 25 to cam inward slightly as reciprocating element 17 moves away from DC motor 60. Once fingers 25 are beyond protrusions 26, the door will continue to close under the bias of the door closer (not shown).

With reference to Fig 1 , it may be appreciated that one embodiment of the present invention includes means for deactivating motor 60 once it has been

actuated. In particular, cam 63 has glued thereon magnet 70. Positioned above the path of cam 63 are first and second reed switches 71 and 72, which are mounted to base 50 by insulating blocks 140. The locations of reed switches 71 and 72 are such that they are directly over magnet 70 when cam 63 is in the latched (Fig. 1) and unlatched (Fig. 2) positions, respectively. Thus, once motor 60 has been actuated to drive cam 63 in either direction, reed switches serve to detect when the cam 63 has moved far enough to require that motor 60 be de-energized. A primary feature of the present invention is that the above-described latch will move to an unlatched position not only when smoke is detected, but also when the voltage of the power source falls below a predefined threshold. As shown in

Fig. 5, a commercially available smoke detector integrated circuit chip 80 ^* Motorola 14467-1) drives one side of a dual flip flop 90. Pin 15 of smoke detector chip 80 receives an input voltage from a particle detector 81. Input pin 15 of smoke detector chip 80 will receive a low when particle detector 81 does not detect smoke. When particle detector 81 detects smoke, pin 15 of smoke detector chip 80 will receive a high. When pin 15 of smoke detector chip 80 receives a high, pin 10 of smoke detector chip 80 outputs a train of high pulses.

Pin 5 of smoke detector chip 80 is tied to the positive terminal of battery 100 through LED 82 in series with a 150 ohm current limiting resistor 83. Pin 5 of smoke detector chip 80 is temporarily set low on periodic intervals by smoke detector chip 80 to allow current to flow through LED 82 and resistor 83. This causes LED 82 to emit a strobe of light. Smoke detector chip 80 internally measures the voltage of battery 100 from the current flowing into pin 5. Pin 10 of smoke detector chip 80 also outputs a train of high pulses when the voltage of battery 100 drops below 7 volts.

Pin 10 of smoke detector chip 80 is connected to pin 6 of dual flip flop 90 (CD4013). Pin 1 of dual flip flop 90 is the output of the first flip flop, and pin 13 is the output of the second flip flop. When power is initially applied to the circuitry, the output of pins 1 and 13 of dual flip flop 90 are latched low in the following manner. When pin 4 of dual flip flop 90 receives a high, pin 1 of dual flip flop 90 is latched low until pin 6 of dual flip flop 90 receives a high. Likewise*, when pin 10 of dual flip flop 90 receives a high, pin 13 of dual flip flop 90 is latched low until pin 8 of dual flip flop 90 receives a high.

On initial power-up, pin 4 of dual flip flop 90 is tied high by a combination of a reversed biased diode in parallel with a capacitor 91 in series with the positive terminal of battery 100. This causes pin 1 of dual flip flop 90 to be latched low. A millisecond later, the capacitor becomes fully charged and combination 91 becomes an open circuit to DC current. Pin 4 of dual flip flop 90 is then tied to ground through 10K ohm current limiting resistor 92.

Also on initial power-up, pin 10 of dual flip flop 90 is tied high by a combination of a reversed biased diode in parallel with a capacitor 91' in series with the positive terminal of battery 100. This causes pin 13 of dual flip flop 90 to be latched low. A millisecond later, the capacitor becomes fully charged and combination 91' becomes an open circuit to DC current. Pin 10 of dual flip flop 90 is then tied to ground through 10K ohm current limiting resistor 92'.

A darlington pair npn transistor 93 has its collector tied high. A darlington pair npn transistor 94 has its collector tied to the emitter of darlington transistor 93 at node 99. The emitter of darlington transistor 94 is tied to ground.

Likewise, a darlington pair npn transistor 95 has its collector tied high. A darlington pair npn transistor 96 has its collector tied to the emitter of darlington transistor 95 at node 120. The emitter of darlington transistor 96 is tied to ground.

The bases of darlington transistors 93 and 96 are tied to pin 1 of dual flip flop 90 through resistors 93' and 96', respectively. The bases of darlington transistors 94 and 95 are tied to pin 13 of dual flip flop 90 through resistors 94' and 95', respectively.

On initial power up, pins 1 and 13 of dual flip flop 90 are latched low as described above. This prevents current from flowing through any of the darlington transistors, 93, 94, 95 and 96. When pin 6 of dual flip flop 90 receives a high, pin 1 of dual flip flop 90 is latched high until pin 4 of dual flip flop 90 receives a high. Pin 1 of dual flip flop 90 provides base current to darlington transistors 93 and 96. This allows current to flow from the collector to the emitter of darlington transistors 93 and 96. This creates a positive voltage between nodes 99 and 120. The DC motor 60 receives its power from nodes 99 and 120. The positive voltage at nodes 99 and 120 causes the DC motor 60 to rotate shaft 67 in a clockwise direction withdrawing cam 63 from between the posterior protrusions 36. This allows latch arms 30 to move freely, releasing fingers 25 and allowing the door close under the power of the door closer.

As shown in Figs. 1 and 2, a permanent magnet 70 is affixed to cam 63. The positive terminal of battery 100 is connected to pin 4 of dual flip flop 90 through second reed switch 72. Second reed switch 72 is positioned across the path of cam 63 as shown in Fig. 2. Once the magnet 65 is sufficiently close to reed switch 72, the reed switch closes pulling pin 4 of dual flip flop 90 high. This causes pin 1 of dual flip flop 90 to be latched low, stopping current from flowing through darlington transistors 93 and 96. This turns off DC motor 60, stopping cam 63 from being withdrawn further.

In this state, a door cannot be latched open. To allow the u .vention to latch open a doo, , cam 63 must be inserted between the posterior protrusions 36. This is accomplished by reset switch 103 that must be manually depressed. Reset switch 103 closes a circuit from pin 2 to pin 8 of dual flip flop 90. Output of pin 2 of dual flip flop 90 is latched high only when pin 1 of dual flip flop 90 is latched low. In the state just described, pin 2 of dual flip flop 90 is latched high. When reset switch 103 is depressed, it momentarily pulls pin 8 of dual flip flop 90 high. When pin 8 of dual flip flop 90 receives a high, pin 13 of dual flip flop 90 is latched high until pin 10 of dual flip flop 90 receives a high. Pin 13 of dual flip flop 90 provides base cur ^c, nt to darlington transistors 94 and 95. This allows current to flow from the collector to the emitter of darlington transistors 94 and 95. This creates a negative voltage between nodes 99 and 120. The negative voltage at nodes 99 and 120 causes DC motor 60 to rotate shaft 67 in a counterclockwise direction, inserting cam 63 between the posterior protrusions 36. This forces the latching ends of latch arms 30 inward around the fulcrum of pins 32, allowing latch arms 30 to latch fingers 25. The positive terminal of battery 100 is connected to pin 10 of the dual flip flop 90 through first reed switch 71. First reed switch 71 is positioned across the path of cam 63 as shown in Figs 1 and 2. Once magnet 70 is sufficiently close to first reed switch 71, it closes pulling pin 10 of the dual flip flop 90 high. This causes pin 13 of dual flip flop 90 to be latched low, stopping current from flowing through darlington transistors 94 and 95. This turns off DC motor 60, stopping cam 63 from being inserted further.

It is obvious that if the invention is reset to a latch mode while a c^~ ition exists which causes the invention to unlatch, cam 63 will be automatical!., withdrawn as soon as it reaches its latch open position. This results because pin 6 of dual flip

flop 90 will continue to receive a high and pin 4 of dual flip flop 90 will not be tied high through second reed switch 72 after cam 63 leaves the unlatched position.

Two final conditions will cause the invention to automatically unlatch. First, referring to Fig. 6, a mechanical switch 104 is connected to an access member comprising lever 121 attached to a battery compartment 122 housing a standard 9 volt battery 100. Before battery 100 may be grasped and thereby disconnected from electrical contacts 123, which comprise a power supply receiving means, lever 121 must be raised to the position designated as 130, which trips switch 104. In this state, switch 104 closes a circuit from pin 12 of dual flip flop 90 to pin 6 of dual flip flop 90. Pin 12 of dual flip flop 90 is high only when pin 13 of dual flip flop 90 is low. Once pin 6 of dual flip flop 90 receives a high, the invention operates as described above for the detection of smoke or low battery voltage, and the device is unlatched before battery 100 may be removed from compartment 122.

An alternate battery access member is shown in Fig. 7. In this embodiment, screws 175 and 176 hold plate 170 to housing 11. Screw 175, which acts as a battery access member, is positioned to depress plunger 172 of switch 173 when screw 175 is fully screwed into housing 11. Before battery 100 may be disconnected from battery clip 174, screws 175 and 176 must be removed in order to separate plate 170 from housing 11. As screw 175 is retracted, switch 173 will trip, causing the door to become unlatched as described above.

The second condition that will cause the invention to automatically unlatch occurs when test switch 84 is depressed to complete a circuit from the positive terminal of battery 100 to the ground terminal of battery 100 through two-1M ohm resistors 86 and 85 wired in series. As shown in Fig. 5, input to particle detector 81 is connected via the first 1M ohm resistor 86 to the positive terminal of battery 100. When switch 84 is depressed, particle detector 81 generates a false smoke detection signal to pin 15 of smoke detector chip 80. Smoke detector chip 80 behaves as though smoke was detected and pin 10 of smoke detector chip 80 outputs a train of high pulses. The device then functions as previously described. The attached Appendix A shows source code software for implementing the above procedures on the above specified microprocessor IC3.

As noted above, the above components may be contained in a single housing.

It will be appreciated that numerous changes may be made to the embodiment disclosed herein without departing from the spirit and scope of the invention. For example, numerous latch mechanisms for door closers are known in the art and may be employed in place of the finger/latch arm combination described above. In particular, any latch mechanism based on the use of a reciprocating member could be replaced by the motor-threaded sleeve combination disclosed above. For example, such a reciprocating member could be inserted and retracted from a detent in a rotatable cylinder, as disclosed in U.S. F.^ent Nos. 3,729,771 or 3,935,614. It is also contemplated that a door closer may be integrally constructed with a door hold open device, instead of using separate units. In addition, many other variations of power supply access members which trip a switch, including those based on movement, touch, capacitance, light and other techniques, may be used to cause unlatching of the door before disconnection of the power supply. The above described embodiment contains several advantages over the prior art. First, the use of a DC motor makes constant current to the electrical actuating element unnecessary. Second, since a large constant current is not needed, a battery may be used as a power source. This in turn makes wiring the device to a building's electrical supply unnecessary. Third, since the device is not wired to a building's electrical supply, it will not be damaged by power spikes, and the chances of incorrectly wiring of the device are eliminated. Fourth, the device will not unlatch if there is a power failu*^ in the building. Fifth, if a fire occurs, only doors in the area of the fire will close, as remote doors will remain held open. Sixth, the switch on the battery compartment which releases the door from the held open position if the battery is removed, provides compliance with many fire codes, which demand that such devices unlatch when power to a door hold open device is interrupted. Additionally, the device may be used with any other door closer. Finally, the voltage threshold detector causes the device to unlatch a held-open door before the battery's voltage drops to a level where it is insufficient to power the unlatching mechanism.

Other modes of applying the principles of the invention are possible provided that the features stated in the following claims, or the equivalent of such, be employed.

Referring to Fig. 8, a second embodiment of the device of the invention is shown. In this embodiment, the latching mechanism is operated by servo motor 110 connected to a battery 100 through electronic circuity described in detail below. As the door moves from a closed to an open position, rod 14 translates the door's movement to reciprocating member 17 which moves from the unlatched position shown in Fig. 9 to the latched position shown in Fig. 8. Fingers 25 are positioned to engage latch arms 30 and thereby keep reciprocating member 17 in a hold- open position.

Servo motor 110, which in the preferred embodiment comprises a 94102 servo controller manufactured by Sanwa Electronic Instrument Company of Singapore and distributed by Airtronics, Inc., is mounted in housing 11. Servo motor 110 rotates disc 113 by an amount determined by a modulated signal as described below. Disc 113 is connected by linkage arm 112 to elliptical cam 111. When disc 113 is in the position shown in Fig. 8, linkage arm forces cam 111 toward a latched position. When disc 113 rotates 90' to the position shown in Fig. 9, linkage arm 112 forces elliptical cam 111 into an unlatched position. Precise rotation of the disc 113 by servo motor 110 is achieved by modulating the signals to servo motor 110 as described below.

When servo motor 110 is energized to move disc 113 and elliptical cam 111 into an unlatched position, latch arms 30 are able to move freely. With elliptical cam 111 rotated so its widest portion engages posterior protrusions 36 as shown in Fig. 8, a door may be latched open. This is accomplished by opening the door, thus forcing reciprocating member 17 toward motor 110, until fingers 25 reach latch arms 30. At that point, a slight additional opening force must be applied to the door to force resilient fingers 25 toward each other and between latch arms 30.

Once the protrusions 26 on resilient fingers 25 have passed protrusions 35 of latch arms 30, reciprocating member 17 will be latched as shown in Fig. 8. This results in holding the door open until elliptical cam 111 is rotated 90°, allowing latch arms 30 to pivot freely. At this point, the bias of door closer (not shown) will begin to close the door, moving reciprocating member 17 away from motor 110. This motion will cause fingers 25 to push latch arms 30 outward; unlatching reciprocating member 17.

Even when the hold-open device is in its latched position as shown in Fig. 8, the door may be closed by manually applying a closing force to the door sufficient

to cause resilient fingers 25 to cam slightly inward as reciprocating element 17 moves away from servo motor 110. Once fingers 25 are beyond protrusions 26, the door will continue to close under the bias of the door closer (not shown).

A primary feature of the present invention is that a signal processing means such as a microprocessor having data input (A2, A3) and output (B2, B3 and B6) means and a power source means (VCC) is utilized to generate the modulated current necessary to drive servo motor 110, and circuitry is utilized to prevent the microprocessor from consuming power until a separate circuit detects an event which may indicate an unlatch condition. The term "signal processing means" is defined to mean a means for converting the electric waveform of an unlatch condition signal into a waveform capable of actuating the unlatch mechanism. Thus, the microprocessor conserves energy by requiring minimal power consumption during normal operation.

Referring to Fig. 10, the circuit of the second embodiment of the present invention can be divided into two general sections, namely, a unlatch condition detection circuit, and a servo/controller circuit. The unlatch detection circuit generates an unlatch signal under any of four occurrences, namely the detection of smoke, a low battery condition, the depression of a test button, or the tripping of a switch indicating that the power source (battery) may be disconnected. The circuit has three general modes: (1) standby mode, in which the circuit is "waiting" for an unlatch condition to occur; (2) unlatch mode, in which the circuit causes servo motor 110 to be moved into an unlatched position; and (3) reset mode, in which servo motor 110 is moved from an unlatched into a latched position. The circuit is powered by a standard 9 volt transistor battery 100. Servo/Controller Circuit Section- Standby Condition. During the standby condition output pin 10 (Fig. 10) of smoke detector integrated circuit IC1 remains low. Since this output is low, transistors Q1, Q2, and Q3 are off; therefore no power is applied to 5v regulator IC2 (LM78L05) and in turn no power is applied to microprocessor IC3 (Microchip PIC 16C54), servo motor 110, or its driver transistors Q7, Q8 and Q9. This condition, in which microprocessor is prevented from consuming electrical current, results in extremely low standby current drain for maximum battery life.

Unlatch Condition. An unlatch condition causes the circuit to enter an unlatch mode. An unlatch condition may be depression of test switch SW1 ,

accessing the battery to actuate switch SW3, detection of smoke by smoke sensor 202, or the detection of a low battery condition by IC1 , any of which causes a high pulse from output pin 10 of smoke detector integrated circuit IC1 (Motorola 14467- 1). This pulse signal turns on transistor Q1, which in turn activates transistors Q2 and Q3. Transistor Q3 applies power to 5v regulator IC2 which then provides electrical current to microprocessor IC3. Within the first 20 milliseconds, microprocessor IC3 acts partially as a swans and enables its output port B2 (pin #8). Port B2 turns on transistors Q4 and Q5 to latch power on to microprocessor IC3. During this time, the signal from the smoke detector, (IC1, pin #10) is also buffered and inverted by transistor Q6 and applied to input port A3 of microprocessor IC3. After port B2 (pin #8) has been enabled, microprocessor IC3 examines input ports A3 and A2 (pins #2 and #1 respectively) to determine the continued existence of the unlatch condition signal. (Port A2 is active only when the reset button is depressed - see Reset Condition below.) When an unlatch condition signal is detected at port A3 (pin #2), microprocessor IC3 enables output port B6 (pin #12). Enabling port B6 turns on transistors Q7, Q8, and Q9 to supply power to servo motor 110. Microprocessor IC3 then sends pulse signals of the proper width from port B3 (pin #9) to servo motor 110 to cause the latch to be released. Once servo motor 110 has rotated 90° to its proper position to release the door, microprocessor IC3 disables ports B6 and B2 (pins #12 and #8 respectively) to conserve battery power. No further action is taken until the pulse signal present at pin #10 of IC1 ceases and returns.

Reset Condition. A reset condition occurs when reset switch SW2 is depressed, which applies power to transistor Q2. This in turn activates Q3 which applies power to the 5v regulator IC2. IC2 in turn supplies power to microprocessor IC3. After power is applied to microprocessor IC3, within 20 milliseconds, its output port B2 (pin #8) is enabled. This then turns on transistors Q4 and Q5 to maintain power applied to itself. Microprocessor IC3 then immediately checks for activity at port A3 and A2 respectively. If no activity (high condition) is present at port A3 (pin #2), which indicates an unlatch condition, then port A2 (pin #1) is checked. Port A2 should be "0" indicating that reset button SW2 is depressed. The reset button must be depressed for a time period of greater than 250 milliseconds for the reset function to be activated. This "0" at port A2 will cause microprocessor IC3 to enable port B6 (pin #12) which supplies power to servo motor 110 through

transistors Q7, Q8 and Q9. Port B3 (pin #9) will then outr t the correct pulse width signal to cause servo motor 110 to move into a late, .ad position. Once this has been completed, microprocessor will disable ports B6, B2 and B3 to thereby power-down and conserve battery power. No further activity will take place until reset switch SW2 is again depressed (in which case servo motor 110 will not move) or an unlatch condition occurs (IC1 pin #10 becomes high.) If fc .me reason reset switch SW2 was depressed for less than 250 milliseconds, tr,. processor will monitor ports A3 and A2 for 50 seconds. If no activity is detected durinp that time period, the processor will shut itself off and the system will revert to the andby mode.

Unlatch Detection Circuit.

Standby Mode. In standby mode, smoke detector chip IC1 internally powers itself and checks for the presence of smoke every 1.67 seconds. This is accomplish d by comparing the voltage at pin #15 against a reference voltage. If no smoke is detected, IC1 will power itself down to conserve battery power.

Additionally, the LED D3 will be turned on for 10 milliseconds every 40 seconds. During the ON time of the LED, the battery supply voltage is compared to a reference voltage to determine if a low battery condition exists.

Unlatch Condition. When either test switch SW3 is depressed or the battery access door switch SW3 is tripped, the voltage at pin #15 of IC1 will be forced below the reference voltage required to determine the presence of smoke. Pin #10 of IC1 will then output an unlatch condition signal in the form of pulses as long as either of these conditions exists. These pulses will then cause controller/servo circuit 201 to release the door latch, as described above. If smoke enters the smoke sensor 202, the conductivity between point A and ground of the smoke sensor is changed. This change results in a voltage drop, at pin #15 of IC1, which is again compared against the voltage reference and results in opening the door latch as described above. When a low battery condition is detected by IC1, a 10 millisecond pulse is present at pin #10 of smoke detector IC1 every 40 seconds. The first pulse will cause controller circuit 201 to "wake up" f" m its standby condition and wait for 50 seconds for the next pulse. The next pulse will cause servo motor 110 to move to an unlatched position. The circuit will then revert to standby mode.

A flowchart for the software used by the microprocessor appears in Fig. 11. As discussed above, microprocessor IC3 receives no power when in standby condition. However, when power is initially applied to microprocessor IC3 as a result of an unlatch condition signal, microprocessor IC3 generates a high signal out of its output port B2, which, as described above, activates a circuit switch to maintain power to microprocessor IC3. Microprocessor IC3 also checks an internal clock time as a time reference, then checks port A3, which is the unlatch condition signal input port. If an unlatch condition signal is still present at port A3, microprocessor IC3 generates a series of modulated output pulses out of output port B6 which cause servo motor 110 to move into an unlatched position. For the 94102 servo controller motor utilized in the preferred embodiment, this modulated signal consists of a 1.8 millisecond high pulse, which is repeated every 15 milliseconds. In addition, microprocessor IC3 sets a flag in memory to indicate that the door holder is in an unlatched position. The system then repeats this process until an unlatch condition signal is no longer present at input port A3.

If, however, after the above power maintenance step, there is not an unlatch signal condition present at input port A3, different steps are taken. (A high signal may not always still be present at the output of pin 10 if IC1, even though this signal initially activates the microprocessor. This is because the signal out of pin 10 of IC1 is a pulsed signal, which lasts only a short duration. Thus, the time it takes for microprocessor IC3 to reset as described above may be longer than the pulse duration from IC1. However, microprocessor IC3 will detect the following pulse within fifty seconds and generate an unlatch signal upon such detection.) A check of the flag is made to determine whether the latch has been unlatched. If so, output port B2 is deactivated, which turns off IC2 and thereby the power to microprocessor IC3. This also automatically resets the flag. The circuit then enters standby mode as described above, with the latch unlatched, until the next unlatch condition occurs.

If the flag has not been set, then input port A2 is monitored to see if the reset button is depressed. If so, then a series of 1 millisecond pulses (each separated by a 15 millisecond period) is output from port B6, which causes servo motor 110 to move into a latched position. Thereafter, port A3 is monitored to see if an unlatch condition exists. If so, control returns to the point shown in Fig. 11. If not, the system turns off port B2 and enters standby mode.

If port A2 is not active, then the system checks the internal clock and compares it to the above-described reference time to see whether fifty seconds have elapsed since port A3 was initially activated. This check, which constitutes a timer, accounts for the fact that there is a 40 second interval between low battery condition pulses, and the first pulse may no longer be present when port A3 is checked as described above. Therefore, checking continues for a 50 second period, and if a low battery condition exists, the second pulse into port A3 will be detected. However, if 50 seconds pass without a pulse reappearing at port A3, the system resets and returns to standby mode to conserve power. Although in the preferred embodiment the unlatch condition signal comprises a pulsed signal in which each pulse may be separated by a duration of up to 50 seconds, any other form of signal may be employed to communicate the existence of an unlatch condition. Moreover, although the signal processing means in the preferred embodiment comprises a microprocessor, the microprocessor could easily be replaced by a comparable combination of hard-wired circuitry. In the preferred embodiment, when power is initially provided to the microprocessor upon an unlatch condition, the microprocessor verifies the continued existence of the unlatch condition signal before applying an unlatching signal to the door latch. However, this verification step could easily be eliminated. The above described embodiment contains several advantages over the prior art. Most importantly, the use of an unlatch condition signal to both indicate an unlatch condition and to also turn on a power source to a microprocessor significantly reduces power consumed by the microprocessor during standby conditions. This greatly increases battery life. In addition, the microprocessor includes logic to detect smoke, low battery, test and reset conditions, as well as the logic necessary to generate modulated signals for the servo motor and to generate a signal to maintain power to the microprocessor once an unlatch condition has been detected. This construction greatly reduces the number of parts and cost of the door holder.