Abstract:
Within an illuminating pushbutton switch, an electronic circuit replaces an electromagnetic holding coil for latching or releasing a state of the illuminated pushbutton switch, and further provides blinking functionality. The electronic circuit includes inputs receiving set, reset and toggle control signals, outputs delivering open, closed and blink control signals, latch logic controlled by the set and reset control signals and delivering signals maintaining the illuminated pushbutton switch in either an open or closed state, and a frequency divider and oscillator coupled together to deliver a blink control signal. The electronic circuit fits within the illuminated pushbutton switch housing in space sized to hold two snap action switching devices without increase in the length, weight or mounting depth of the illuminated pushbutton switch. The inputs and outputs are coupled to external pins from the illuminated pushbutton switch and may be remotely controlled.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    This application claims priority to commonly assigned U.S. Provisional Patent Application No. 61/207,016, filed Feb. 6, 2009, which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is directed, in general, to illuminated pushbuttons switches, and more specifically to implementing electronic latching and blinking features for illuminated pushbutton switches. 
       BACKGROUND 
       [0003]    Within the realm of illuminated pushbutton switch usage, specialized applications are emerging requiring inclusion of latching, blinking or remote control functions to be included within the illuminated pushbutton switch housing. Such applications may require depressing the pushbutton switch to initiate a remote action request, activating switch functions from a remote location, energizing or blinking a local or remote display, and resetting the switch state automatically upon remote acknowledgement. Other applications may involve a plurality of illuminated pushbutton switches in differing locations, all controlling the same functions, wherein a switch depressed at one location must change the state of a switch or display at another location. Nearly all applications require the added safety feature of an automatic reset to a default state after loss of power. 
         [0004]    Proposed designs may incorporate local latching and remote release functions through the use of internal electromagnetic holding coils, in some cases together with various electronic or electromechanical means to interrupt the holding coil current locally without remote intervention. Many of the proposed designs that rely upon an internal electromagnetic holding coil suffer from excessive power consumption, excessive heat, sensitivity to shock and physical jarring, electrical spikes, holding coil drop-out on low voltage, and low reliability. The internal holding coil also makes the resulting illuminated pushbutton switch substantially longer and heavier than standard models that do not incorporate a holding coil. 
         [0005]    There is, therefore, a need in the art for improved latching and release in pushbutton switches, together with other features. 
       SUMMARY 
       [0006]    Within an illuminating pushbutton switch, an electronic circuit replaces an electromagnetic holding coil for latching or releasing a state of the illuminated pushbutton switch, and further provides blinking functionality. The electronic circuit includes inputs receiving set, reset and toggle control signals, outputs delivering open, closed and blink control signals, latch logic controlled by the set and reset control signals and delivering signals maintaining the illuminated pushbutton switch in either an open or closed state, and a frequency divider and oscillator coupled together to deliver a blink control signal. The electronic circuit fits within the illuminated pushbutton switch housing in space sized to hold two snap action switching devices without increase in the length, weight or mounting depth of the illuminated pushbutton switch. The inputs and outputs are coupled to external pins from the illuminated pushbutton switch and may be remotely controlled. 
         [0007]    Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0009]      FIGS. 1A ,  1 B and  1 C are exploded perspective views of a pushbutton illuminated switch (or components thereof) with electronic latching and/or blinking according to one embodiment of the present disclosure; 
           [0010]      FIGS. 1D and 1E  are perspective views illustrating incorporation of an electronic latching and/or blinking module into the pushbutton illuminated switch of  FIGS. 1A-1C ; and 
           [0011]      FIG. 2  is a circuit diagram for an electronic latching and/or blinking module according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIGS. 1A through 2 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system. 
         [0013]      FIGS. 1A ,  1 B and  1 C are exploded perspective views of a pushbutton illuminated switch (or components thereof) with electronic latching and/or blinking according to one embodiment of the present disclosure. The pushbutton switch  100  includes a switch cap  101  and a switch body  102 . The switch cap  101  is located at the front of the switch  100  and is received by the switch body  102 . The switch cap  101  includes a switch cap housing  103  receiving an array  104  of surface mount diode (SMD) light emitting diodes (LEDs). The 2×4 LED array  104  in the exemplary embodiment has two rows of four LEDs arranged to illuminate four quadrants of a face plate (not shown) on the front of switch cap body  103 , with two LEDs (a 1×2 subarray) per quadrant. The LEDs are mounted over a switch cap back plate  105  and are connected to an electrical driving circuit (not visible in  FIG. 1B ) mounted on the switch cap back plate  105 . A member  106  for mechanical latching and release of the pushbutton switch when the switch cap  101  is depressed within the switch body  102  protrudes from the rear of switch cap back plate  105 . Electrical connections (not shown) to the driving circuit are also exposed on the rear surface of switch cap back plate  105 . 
         [0014]    Switch body  102  includes a housing  107  receiving a mechanical and electrical subsystem  108  for mechanical latching and release of the pushbutton switch  100 , for transmitting electrical signals to the driving circuit, and for transmitting mechanical forces to actuate four-pin snap-action switching devices  109   a  through  109   d.  Pins for the switching devices  109   a  through  109   d  are received by mounting block  110  and provide electrical switching by connections of the pins to external signal sources and/or through the subsystem  108  to the driving circuit. The pins of devices  109   a  through  109   d  extend through the mounting block  110  and may be connected at the rear of pushbutton switch  100  to external signals, to each other, and/or through subsystem  108  to the driving circuit. 
         [0015]    Those skilled in the art will recognize that the complete structure and operation of a pushbutton switch of the type normally used in avionics is not depicted or described herein. Instead, for simplicity and clarity, only so much of the structure and operation of a pushbutton switch as is necessary for an understanding of the present disclosure is depicted and described. For example, filters between the LEDs and the switch cap face plate allow legends on the switch cap face plate to be illuminated in different colors as disclosed in U.S. Pat. No. 6,653,798, which is incorporated herein by reference. Numerous other features are also not depicted or described herein are or may be included within pushbutton switch  100 . 
         [0016]      FIGS. 1D and 1E  are perspective views illustrating incorporation of an electronic latching and/or blinking module into the pushbutton illuminated switch of  FIGS. 1A-1C . As shown in  FIG. 1D , an electronic latching and/or blinking module  111  is inserted in place of switching devices  109   b  and  109   c,  with pins received by mounting block  110 .  FIG. 1E  depicts a mounting frame  112  on which integrated electronic circuitry may be mounted, within one of the recesses  113 . The electronic module  111  is coupled to a plurality of interface pins  114  (eight in the exemplary embodiment) each extending from the electronic circuitry through a portion of the mounting frame  112  to an endpoint and configured to pass through additional frames or housings (not shown) and engage additional electronic circuitry (not shown), in the same manner as pins for switching devices  109   b  and  109   c.  This approach provides the added functionality of the electronic module  111  with no increase in length, weight or mounting depth while retaining two uncommitted snap-action switching devices  109   a  and  109   d  that can be used to interact with the electronic module  111  or control other system functions. 
         [0017]      FIG. 2  is a circuit diagram for an electronic latching and/or blinking circuit according to one embodiment of the present disclosure. Electronic latching and/or blinking circuit  200  is contained within the electronic module  111  within switch  100 . TABLE I below contains the input and output signal descriptions for circuit  200 , while TABLE II describes the logic input and output functions: 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 SIGNAL 
                   
                 ACTIVE 
                   
               
               
                 NAME 
                 FUNCTION 
                 STATE 
                 DESCRIPTION 
               
               
                   
               
             
             
               
                 /RESET 
                 Input 
                 Low 
                 Forces /N_OPEN to OFF (open). 
               
               
                   
                   
                   
                 Forces /N_CLOSED to ON (ground). 
               
               
                   
                   
                   
                 Forces /BLINK to Steady ON (ground). 
               
               
                   
                   
                   
                 See Note 1 below. 
               
               
                 /TOGGLE 
                 Input 
                 ↓ 
                 Toggles /N_OPEN and /N_CLOSED outputs. 
               
               
                   
                   
                   
                 Toggles blink mode. See Note 2 below. 
               
               
                 /SET 
                 Input 
                 Low 
                 Forces /N_OPEN to ON (ground). 
               
               
                   
                   
                   
                 Forces /N_CLOSED to OFF (open). 
               
               
                   
                   
                   
                 Initiates 1 Hz blink mode to /BLINK output. 
               
               
                 +28 VDC 
                 Power 
                 — 
                 Power (+10 VDC to +30 VDC) 
               
               
                 Ground 
                 Common 
                 — 
                 Common for power and signals. 
               
               
                 /N_OPEN 
                 Output 
                 Low 
                 Open drain output. 
               
               
                   
                   
                   
                 Forced OFF (open) by /RESET input. 
               
               
                   
                   
                   
                 Forced ON (ground) by /SET input. 
               
               
                   
                   
                   
                 Toggled by falling edge of /TOGGLE input. 
               
               
                 /N_CLOSED 
                 Output 
                 Low 
                 Open drain output. 
               
               
                   
                   
                   
                 Forced ON (ground) by /RESET input. 
               
               
                   
                   
                   
                 Forced OFF (open) by /SET input. 
               
               
                   
                   
                   
                 Toggled by falling edge of /TOGGLE input. 
               
               
                 /BLINK 
                 Output 
                 Low 
                 Open drain output. 
               
               
                   
                   
                   
                 Forced ON (ground) while /RESET is held low. 
               
               
                   
                   
                   
                 See TABLE II below. 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Inputs 
                 Outputs 
               
             
          
           
               
                 /SET 
                 /RESET 
                 /TOGGLE 
                 /N_OPEN 
                 /N_CLOSED 
                 /BLINK 
               
               
                   
               
               
                 L 
                 H 
                 X 
                 L (ground) 
                 H (open) 
                 1 Hz blink 
               
               
                   
                   
                   
                   
                   
                 mode. 
               
               
                 H 
                 L 
                 X 
                 H (open) 
                 L (ground) 
               
               
                 L 
                 L 
                 X 
                 See Note 3. 
                 See Note 3. 
                 Steady ON. 
               
               
                   
                   
                   
                   
                   
                 See Note 1. 
               
               
                 H 
                 H 
                 ↓ 
                 Toggle 
                 Toggle 
                 Toggle. 
               
               
                   
                   
                   
                 state. 
                 state. 
                 See Note 1. 
               
               
                   
               
               
                 Note 1: 
               
               
                 /BLINK output is held steady ON (ground) while /RESET is held low. /BLINK output goes OFF (open) when /RESET returns to the inactive high level. This feature provides essentially three states to the /BLINK output: OFF, ON and BLINK. 
               
               
                 Note 2: 
               
               
                 /TOGGLE input causes /BLINK output to alternate between 1 Hertz (Hz) blink state and OFF (open). 
               
               
                 Note 3: 
               
               
                 This is an illegal state that will have unpredictable effect upon the outputs when the inputs are returned to their normal inactive high state. 
               
             
          
         
       
     
         [0018]    The logic input circuitry  201  for has a total of eight (8) interface pads each connected to an external pin of electronic module  111 . Three interface pads are inputs: /SET, /RESET and /TOGGLE. Three interface pads are outputs: /N_OPEN (normally open), /N_CLOSED (normally closed) and /BLINK. Two additional interface pads are devoted to power: +28 VDC (volts, direct current) and Ground. 
         [0019]    Each input pad is connected by two parallel resistors: resistors R 1  and R 2  for input /SET; resistors R 3  and R 4  for input /TOGGLE; and resistors R 5  and R 6  for input /RESET. One resistor of each parallel pair (R 1 , R 3  and R 5 ) is connected at the other terminal to the +28 VDC input power. The other resistor of each pair (R 2 , R 4  and R 6 ) is connected to one terminal of a capacitor (C 1 , C 2  and C 3 , respectively) and to the cathode of a zener diode (D 1 , D 2  and D 3 , respectively). The other capacitor terminals and the anodes of the zener diodes are connected to ground. Resistors R 1 , R 2 , R 3 , R 4 , R 5  and R 6  each have a resistance of 33 kilo-Ohms (KΩ). Capacitor C 1  has a capacitance of 0.1 micro-Farads (μF) and each of capacitors C 2  and C 3  has a capacitance of 1.0 μF in the example depicted. 
         [0020]    Each input to circuit  200  includes input filter circuitry designed to protect the integrated circuits from EMC, voltage transients, electromechanical contact bounce and shift the 28 VDC logic level to a 5 VDC logic level. 
         [0021]    Resistors R 2 , R 4  and R 6  and zener diodes D 1 , D 2  and D 3  provide electromagnetic charge (EMC) protection and voltage transient protection to circuit  200 , and shift the 28 VDC logic level to a 5 VDC logic level. Furthermore, complementary metal-oxide-semiconductor (CMOS) latch-up on extreme transients such as lightning or a conducted electromagnetic pulse (EMP) is prevented by clamping the inputs 0.5 VDC below the logic power supply voltage. Capacitors C 1 , C 2  and C 3  suppress electromechanical contact bounce. Resistors R 5  and R 6  and capacitor C 3  on the /RESET input guarantee a default power-up state for circuit  200  since the power-up time constant of those components is substantially longer than that of both the logic power supply VCC (which has a lower resistance) and the /SET input (which has a much smaller capacitance). Pull-up resistors R 1 , R 3  and R 5  establish a default static logic level for the inputs, preventing floating logic states on unconnected inputs. 
         [0022]    The logic power supply functional unit  202  generating the logic power supply voltage VCC for circuit  200  includes resistor R 7  (which has a resistor of 15 KΩ), zener diode D 4  and capacitor C 4  (which has a capacitance of 1.0 μF) from the +28 VDC power input. Due to the low operating current of the CMOS logic circuitry within circuit  200 , the value of resistor R 7  is selected to limit the current of any EMC or voltage transient on the +28 VDC power pad. Transient suppression and voltage regulation on the +5.6 VDC logic power supply is provided by D 4  while C 4  provides filtering of input and logic transients. Because the logic power supply is a simple shunt voltage regulator, circuit  200  can operate over a wide input voltage range from below +10 VDC to in excess of +30 VDC. 
         [0023]    Circuit  200  includes two high speed CMOS integrated circuits: a dual D-Type latch (FF 1  and FF 2 ) and a quad NAND gate (NAND 1 , NAND 2 , NAND 3  and NAND 3 ) implementing the latch logic  203  and the blink circuitry  204 . The inverted preset input PRE of latch FF 1  is connected by resistor R 1  to the /SET input, while the input D of latch FF 1  is connected to the inverting output of latch FF 1 . The clock input CLK of latch FF 1  is coupled by NAND gate NAND 4 , configured as an inverter with the inputs tied together, by resistor R 4  to the /TOGGLE input. The inverted clear input CLR of latch FF 1  is connected by resistor R 6  to the /RESET input. 
         [0024]    Latch FF 1  is the primary latching circuit that responds to the inputs /SET, /RESET and /TOGGLE as described in TABLE II above. NAND gate NAND 4  is connected between the /TOGGLE input and the clock input of latch FF 1  for the purpose of inverting the positive (leading) edge trigger of latch FF 1  to a negative (trailing) edge trigger. The inverting output of latch FF 1  is connected to the D input so that successive /TOGGLE inputs to latch FF 1  result in a toggling action of latch FF 1  non-inverting and inverting outputs Q and /Q. The non-inverting output Q from latch FF 1  drives the normally open output /N_OPEN via n-channel enhancement mode metal-oxide-semiconductor field effect transistor (MOSFET) Q 3 , and the inverting output /Q from latch FF 1  drives the normally closed output /N_CLOSED via MOSFET Q 2 . The non-inverting output Q of latch FF 1  also holds latch FF 2  in the reset state any time latch FF 1  is in the reset state. 
         [0025]    Blink circuitry  204  includes series connected NAND gates NAND 1  and NAND 2  configured as inverters with the respective inputs tied together and are interconnected as a dual inverting buffer that, together with resistor R 8  (having a resistance of 220 KΩ) connecting a feedback loop from the output of NAND gate NAND 2  to the input of NAND gate NAND 1  with the input to NAND gate NAND 2  and capacitor C 5  (having a capacitance of 1.9 μF) connected in the feedback loop, form a free running square wave oscillator with a fundamental frequency F1/(2.2×R 8 ×C 5 ) of approximately 2 Hertz (Hz). The output of that oscillator feeds the clock input CLK of latch FF 2 , where the inverting output /Q of latch FF 2  is connected to the D input so that latch FF 2  functions as f/2 frequency divider. The inverted preset input PRE of latch FF 2  is tied to the logic supply voltage VCC. Because the inverted clear input CLR of latch FF 2  is connected to the non-inverting output Q of latch FF 1 , the f/2 divider circuit is effectively disabled any time latch FF 1  is in the reset state. The f/2 divided frequency output of latch FF 2  creates the 1 Hz blink mode oscillator, enabled only when latch FF 2  is in the set state. 
         [0026]    The enabled 1 Hertz blink signal from the inverting output /Q of latch FF 2  is connected, along with the filtered /RESET input, each to one input of NAND gate NAND3. NAND gate NAND3 thus serves as blink logic, forcing the /BLINK output to be held in a steady ON state any time the /RESET input signal is held low. The output of NAND gate NAND 3  is connected to MOSFET Q 1  to provide the /BLINK output of circuit  200 . 
         [0027]    Each output from the circuit  200  includes a power MOSFET Q 1 , Q 2  or Q 3  each rated at 2.5 ampere (A) at 45 VDC (both parameters chosen to be substantially greater than operational requirements) and an output filter designed to protect each output device from transients and overload conditions. Transient protection for the MOSFETs Q 1 , Q 2  and Q 3  is provided by impedances Z 1 , Z 2  and Z 3 , each having a breakdown voltage of 39 VDC. Overload protection is provided by resettable Positive Temperature Coefficient (PTC) resistors R 9 , R 10  and R 11  with a holding current of 0.5 A at elevated temperatures. These devices perform the function of a fuse, limiting current in the event of a short or overload, but automatically return to their normal state when the short or overload is removed. In order to provide the highest possible reliability, each output /N_OPEN, /N_CLOSED and /BLINK is derated to a maximum operating current of 0.5 A. 
         [0028]    The features of activating switch functions from a remote location, energizing or blinking a local or remote display, resetting the switch state automatically upon remote acknowledgement, changing the state of a switch or display at one location based on another, remote switch controlling the same function being depressed, and automatic reset to a default state after loss of power are implemented in the present disclosure by replacing the traditional electromagnetic holding coil within the illuminated pushbutton switch housing with a subminiature electronic logic module. The logic module provides many additional features beyond the simple latching or on/off toggling functionality that is typical of an electromagnetic holding coil, including lower size and weight, longer switch life, no electrical spikes, remote set and reset capability, display blinking, and high reliability electronic driver circuits that can drive modest electrical loads. 
         [0029]    Although the above description is made in connection with specific exemplary embodiments, various changes and modifications will be apparent to and/or suggested by the present disclosure to those skilled in the art. It is intended that the present disclosure encompass all such changes and modifications as fall within the scope of the appended claims.