CA2023958C - Capacitive sensing, solid state touch button system - Google Patents
Capacitive sensing, solid state touch button systemInfo
- Publication number
- CA2023958C CA2023958C CA002023958A CA2023958A CA2023958C CA 2023958 C CA2023958 C CA 2023958C CA 002023958 A CA002023958 A CA 002023958A CA 2023958 A CA2023958 A CA 2023958A CA 2023958 C CA2023958 C CA 2023958C
- Authority
- CA
- Canada
- Prior art keywords
- button
- pulse width
- phase shift
- voltage
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
- H03K17/96—Touch switches
- H03K17/962—Capacitive touch switches
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/14—Modifications for compensating variations of physical values, e.g. of temperature
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K11/00—Transforming types of modulations, e.g. position-modulated pulses into duration-modulated pulses
Abstract
Abstract CAPACITIVE SENSING, SOLID STATE TOUCH BUTTON SYSTEM
A solid state touch or control button assembly (10), with no moving button parts and operated by capacitive sensing by monitoring the phase shift of a signal applied to the face of the button, including in a first embodiment (Figs. 2A & 2B) a auto balancing button and in a second embodiment (Figs. 3A & 3B) a constant pressure button. If skin or other material comes into contact with the touch surface, the capacitance is changed and sensed, causing the electrical or electronic function controlled by the touch button to be activated (or deactivated, depending on the design, or otherwise altered). LEDs then are activated, providing visual feedback to the button pusher through a light ring (2A) surrounding the button surface (1). False activation of the button by residual impedance and external influences, such as temperature change, cleaner residue build-up and other deposits, are avoided by compensating for them by slowly auto balancing to all such phase shifts, with the rate of auto balance being set to be faster than the rate of change of the steady state phase shift; and, addi-tionally, false activations by noise transients, includ-ing those due to EMI, RFI and other environmental fluctuations, are avoided by delaying the activation of the button by an appropriate amount of time, such as, for example, of the order of about one hundred (100 msec.) milliseconds.
A solid state touch or control button assembly (10), with no moving button parts and operated by capacitive sensing by monitoring the phase shift of a signal applied to the face of the button, including in a first embodiment (Figs. 2A & 2B) a auto balancing button and in a second embodiment (Figs. 3A & 3B) a constant pressure button. If skin or other material comes into contact with the touch surface, the capacitance is changed and sensed, causing the electrical or electronic function controlled by the touch button to be activated (or deactivated, depending on the design, or otherwise altered). LEDs then are activated, providing visual feedback to the button pusher through a light ring (2A) surrounding the button surface (1). False activation of the button by residual impedance and external influences, such as temperature change, cleaner residue build-up and other deposits, are avoided by compensating for them by slowly auto balancing to all such phase shifts, with the rate of auto balance being set to be faster than the rate of change of the steady state phase shift; and, addi-tionally, false activations by noise transients, includ-ing those due to EMI, RFI and other environmental fluctuations, are avoided by delaying the activation of the button by an appropriate amount of time, such as, for example, of the order of about one hundred (100 msec.) milliseconds.
Description
2 ~
[OT-972]
Description CAPACITIV~ 8EN8IN~, 80 ~D 8TATB~TOUC~ BUTTON 8Y8T~M
Technical Fiel~
5The present invention relates to touch buttons typically used to activate or deactivate or otherwise control some electrical or electronic function, such as signaling, when touched typically by a human operator touching or "pushing" on the button with a finger. The invention more particularly relates to a solid state touch button system with no moving parts operated by capacitive sensing, which can be used in many different applications, including, for example, as a touch or push button for elevator car calling or control.
~ackground Art There is a need for a reliable button that does not use or need moving parts or mechanical contacts, to be used in, for example, elevator applications. It is desirable that such a button be aesthetically pleasing in appearance and use, highly reliable, low in cost and not be activated by extreme environmental changes.
It is known that the human body has some amount o~ capacitance to ground. A basic, previously known concept or approach i8 to monitor a button face for capacitance to ground, and, if a certain amount (or greater) capacitance is present, to activate the button.
In the present invention, this monitoring of the button surface is accomplished by monitoring the phase shift of a signal applied to the face of the button.
30However, due to the residual impedance of the button and the presence of external influences, the steady state phase shift of the button can fluctuate.
Such external influences include, for example, tempera-ture changes, cleaner residue build-up and other deposits , - ~ ~ 2 ~
or extreme environmental changes, etc. This fluctuation has the potential to falsely activate a button~ which is based on the monitoring of phase shift, although in fact no human operator is touching the button.
A distinguishing characteristic of such exemplary fluctuation is that it would occur slowly over a period of time relative to a phase shift induced by the presence of a person. To avoid this problem, in a first "auto-balancing" embodiment of the invention the steady state phase shift fluctuation is compensated for by 810wly auto balancing to all phase shifts. The rate of auto balance is set to be faster than the rate of change of the steady state phase shift. The rate of change of phase shifts induced by a person is faster than the auto balance rate, which allows the button to be operated. In a second, "constant pressure" embodiment, another way to compensate for the exemplary fluctuations is to simply set a threshold for activation higher than any normal fluctua-tions.
A second potential source of false activation~ of such a button are phase shifts induced by transient noise. These potential transients include, for example, electromagnetic interference (EMI) and radio frequency interference (RFI).
A distinguishing characteristic used in the invention to help prevent false activations caused by transient noise is that such noise would not last for a long period of time relative to the interaction time with a person. Activations due to transient noise thus are avoided in the invention by delaying the activation of the button for a certain minimum period of time.
Di~clo9ure o~ Invention Thus the present invention is directed to a reliable button that does not need, and preferably does ,' , ~ '-. . ' . : : , '. ;
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not use, any moving parts or mechanical contacts and can be used in, for example, elevator applications.
Additionally, the present invention i8 directed to a button that is aesthetically plea~ing in appearance and use, highly reliable, is low in cost and is not acti-vated by extreme environmental changes.
Finally and most importantly, the present inven-tion is directed to a phase shift monitoring, capacitive sensing button that avoids false activation of the button by residual impedance and external influences, such as temperature change, cleaner residue build-up and other deposits. The "auto-balancing" embodiment of the invention achieves this by compensating for them by slowly auto balancing to all such phase shifts, with the rate of auto balance being set to be faster than the rate of change of the steady state phase shift; while the "constant pressure" embodiment achieves it by compensat-ing for the exemplary fluctuations by simply setting a threshold for activation higher than any normal fluctua-tions. Additionally, the present invention avoids ~alseactivations by nolse transients, including those due to EMI and RFI by delaying the activation of the button, and the associated operative signal that causes it to be activated, by an appropriate amount of time, such as, for example, a time period of the order of about one hundred (100 msec.) milliseconds.
In the exemplary "auto balancing" embodiment, three integrators are used to provide the auto balancing feature o~ the invention. A "medium" speed lntegrator provides a "trigger" signal, while relatively "slow" and "fast" integrators provide "set" and "reset" thresholds.
In accordance with another aspect o~ the inven-tion, the purpose of the delay on the timer is for erroneous signal re~ection, as generally mentioned above.
The erroneous signals of primary concern are those which could be caused by extreme environmental changes.
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Testing has shown that any set pulses caused by exem-plary, extreme environmental changes typically do not last longer than one hundred (100 msec.) millisecond~
with an input resistance of, ~or example, one (l Mn) megohms.
Further testing with the input resistor set to, for example, two hundred and æixt~-one (261 kn) kilo-ohms resulted without any set pulses caused by extreme environmental conditions. From these results a delay "on" time of the order of about one hundred (loO) milliseconds is deemed to be appropriate.
In the exemplary "auto balance" embodiment the delay time is achieved by a set pulse charging a capaci-tor through resistors and a diode to a thre~hold set by other resistors. The voltage across the charging capaci-tor will reach the threshold, ~f a set pulse or series of set pulses transpire without the occurrence of any "reset" pulses.
once the threshold is reached, the output of a comparator is released from common. The voltage on the charging capacitor is pulled up and held high by a hysteresis resistor, pending the occurrence of a "reset"
pulse.
At any time the voltage across the charging capacitor can be quickly discharged by a "reset" pulse.
~ho volt~ge Aaro~ the ahArging capaaitor is discharged through a current llmiting resistor, which resets the timer.
Bene~its o~ the invention include the facts that the button is:
heat resistant;
EMI resistant;
RFI re~i~tant;
ESD resistant; and is capable of providing light and/or other feedback.
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The invention may be pr~cticed in a wide variety of applications, including but not restricted to, elevator car call or control buttons, utilizing known technology, in the light of the teachings of the inven-tion, which are discussed in detail hereafter.
Other ~eatures and advantages will be apparentfrom the specification and claims and from the accompany-ing drawings, which illustrate two exemplary embodiments of the invention, an auto-balancing embodiment and a constant pressure embodiment.
Brlof Desoription of ~raw~ng~
Figure 1 is an exploded, perspective view of an exemplary solid state push button, including the button, light ring, printed circuit (PC) board and holder ~or attaching the PC board to the push button elements and the overall button assembly to a face plate or panel, with the PC board carrying the electrical components which ~orm the exemplary electronics and circuitry of the present invention. (It is noted that the touch button elements of Pigur- 1 are basically symmetrical about their longitudinal center-line, except for the PC board and its associated holder.) Figuros 2A & 2B are interconnected schematic diagrams o~ an exemplary circuit for the button system of the present invention with auto balancing characteris-tics, with the two schematics being connected in the "Delay On Timer" block at the "SET/RESET" line; while Flgures 3a & 3~ are interconnected schematic diagrams o~ an alternate, exemplary circuit ~or the button system of the present invention with constant pressure characteristics, with the two schematics being connected in the "Delay~Dwell Timer" block at the "SET"
line.
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ost ~es ~or C~rry~n~ U~_~he In~t~lon -- ~UTTON A8~MBLY ~10 ) As can be seen in F~gure 1, the exemplary "solid state button" (SSB) 10 of the present invention prefera-bly includes a non-moving, capacitive sensing button surface 1, that can be used, for example, as a call button in the car operating panel (COP) and/or hall fixtures of an elevator system. The SSB is capable of capacitively sensing a human touch, preferably providing lo both visual feed back (illumination) to the button pusher, as well as communication to the operational control of the elevator system through, for example, a remote station interface that the button has been actuated, so that the system accordingly can react.
The exemplary button o~ Figure 1 includes the non-moving button element 1 fitted within a light ring element 2, in which ring i9 carried a circular array of light emitting diodes (LEDs) 3 at its bottom. A printed circuit board ~, into which the light ring element 2 is pin inserted, is carried on the back side of the button elements 1, 2, and is held to the button elements by a bracket S and rear bolt 6.
The interconnecting bolt or stem 7 has a front, threaded, male end 7A, which is screwed into the back side of the button surfaca 1, and a rear, threaded, male end 7B, which is screwed into the ~ront end 6A of the rear bolt 6 with a lock washer 7C. The interconnecting bolt 7 extends through a center, circular opening ~unseen) in the light ring element 2 and through an opening in the PC board ~, while the head 6B of the rear bolt 6 fits into a notch in a "U" shaped rear strap 8, which i9 part of the bracket holder 5. When assembled, the intermediate elements of the button assembly 10 are held in compression between the button surface 1 and the head 6B of the bolt 6.
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The bracket 5 includes a series of peripherally spaced, lateral extensions 9 through which screw pins 9B
are placed for fastening the button assembly 10 to a face plate or panel. When so fastened, the only elements of the button assembly 10 which are seen by the user is the non-moving, circular button surface 1 surrounded by the translucent ring 2A, which is illuminated up by the internally contained LEDs when the button is actuated.
The printed circuit board 4 carries on it the electronic components and circuitry which perform the SSB monitoring functions of the present invention.
There are two basic exemplary embodiment~ of the present invention, a pure "constant pressure" solid state button (CPSSB) embodiment, schematically illus-trated in detail in Figures 3A & 3B, and a relatedpredecessor embodiment, the "auto balancing" solid state button (ABSSB), schematically illustrated in detail in Flgur~8 2A & 2B.
The primary difference between the "constant pressure" solid state button (CPSSB) and the "auto balancing" solid state button (ABSSB) is that the ABSSB
has an auto balancing feature. As generally noted above, the purpose of the auto balancing feature is to automat-ically accommodate for static changes in components, packaging and the environment, while maintaining a relatlvely high sensitivity to sensing when the button aetually has been aetuated. Due to the basic operation of auto balancing, the ABSSB is not a pure, "eonstant pressure" type button and, in the exemplary appliaation of an elevator system, iB not applied to, for example, "door open," "door close" and other applications requir-ing a pure constant pressure (CP) feature. In contrast the CPSSB module can be used, if desired, for all applications in the elevator system except the alarm button, which has special requirements.
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- T~EORY OF OP~ATION -If a button touch is constantly maintained ~or, for example, one hundred (100 msec.) milliseconds, the button module 10 will turn "on" its output and illumina-tion long enough to be read and controlled by theoperational control system without loss of the call or illumination. The illumination input preferably is controlled by the operational control system.
The ABSSB is reset upon the removal of the illumination control input. The illumination control of the CPSS8 can also be used as an output when applied to other systems.
- CIRCUI~ DE8CRIPTION -The basic functions for each embodiment (CPSSB &
ABSSB) are as follows:
Auto-Balance ~ABSSB) Constant Pressure (CPSSB) Power Power Oscillator Oscillator PhaseShiftToPulseWidth PhaseShiftToPulseWidth Converter Converter Integrators Integrators Set&Reset Comparators Level Detector Electrostatic Discharge Electrostatic Discharge (ESD) Protection (ESD) Protection Delay on Timer Delay/Dwell Timer Dwell on Timer Output Control Output Control High Out High Out Illumination Current Illumination Current Regulator Regulator PowerUp & Control System Reset Functions Figure~ 2A & 2B and 3A & 3B are schematics o~ the "auto balance~ embodiment and the "constant pressure~' embodiments, respectively, with these functions outlined in block form.
- POWER -~he power aspects of the two embodiments repre-sent standard approaches and their operation (and many :. :
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2~2~8 alternatives thereto) are known to thosé of ordinary skill.
- 08C~LLATOR -The oscillator generates, for example, a square wave of an appropriate cycle. The threshold voltage to the non-inverting input of comparator Ul~ is set by resistors R2 & R3, and the state of thè output of UlA, which controls the hysteresis resistor R~. The "on"
state threshold is higher than the "off" state threshold.
The oscillator i8 controlled by the charging and discharging of capacitor Cl. When comparator ~lA is in the "on" state, capacitor C1 will charge to the "on"
state threshold, and, as a result, the comparator will turn "off." Conversely, when comparator UlA is in the "off" state, capacitor Cl will discharge to the "off"
state threshold, and, as a result, the comparator will turn "on."
This is standard oscillator circuitry, and its operation and various alternatives are known to those of ordinary skill.
- P~A8E ~HIFT TO PUL~E WIDTH CONVERTER -** Auto B~l~nce 88B **
The phase shift to pulse width converter func-tions as follows. The oscillator is fed directly into the non-inverting input of UlC. When the oscillator is high, the output of UlC is released, providing the rising edge of the pulse. The inverting input of UlB monitors the phase shift o~ the oscillator through resistor R7 across the button input impedance. (The factors which contribute to the button input impedance are the capaci-tor C3, the ESD protection circuit and what is applied to or acquired by the button face.) When the voltage at the inverting input of U~B
reaches the threshold voltage on the non-inverting input, the output of UlB is pulled to common, at the falling edge of the pulse.
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There is always a pulse, even without anything applied to the button face 1. The pulse is due to the impedance of capacitor C3, the ESD protection circuit and any residuals in the circuit.
Capacitor c3 is u~ed to prevent any DC voltage from being placed on the button face. The value of the capacitor C3 should be significantly larger than the capacitive sensitivity to be obtained.
The larger the value of the resistor R7, the larger the phase shift is for a given input impedance, including the effects of resistance and noise. The value of the resistor R7 preferably is chosen to generate as large a phase shift as possible from the input.
** Constant Pres~ure 88B **
Functions on the CPSSB preferably are combined and condensed to reduce the number of required compo-nents. The function of UlC, R~5, and R46 in the "Phase Shift To Pulse Width Converter" block of the ABSSB can be condensed by, for example, replacing them with the diode CR2 on the CPSSB for its "Phase Shift To Pulse Width Converter" block. The functional performance of the pulse width to phase shift converter remains the same.
The integrators convert the pulse into a DC
voltage. The DC voltage i8 equal to the duty cycle of the pulse multiplied by "Vcc," the regulated supply voltage.
** Auto Balance 8~ **
The pulse from the "phase shift to pulse width converter" is fed into three different R-C integrators.
Each integrator has a different time constant, providing relatively "slow" ~R13 x C~), "medium" (R14//R16 x C5) and "fast" (R15 x C6) time constants. The "medium"
integrator has a resistor (R16) in parallel with its capacitor to act as a voltage divider. The voltage divider insures that the steady state DC voltage of the 21~2~ $
"medium" integrator will be less than that of the "slow"
and "fast lntegrators.
The three integrators of Figure 2A provide the auto balancing feature of the invention. The "medium"
S speed integrator provides the "trigger" signal, while the "slow" and "fast" integrators provide the "set" and "reset" thresholds.
The selection criteria for the integrator time constants is given below.
** Constant Pres~ure ~8~ **
In contrast, since the deletion of the auto balance feature is part of the purpose of the CPSSB, only one integrator is required for the CPSSB (F~g. 3A).
- 8ET AND RE8ET COMPARATOR8 AND ~VEL DETECTOR8 -- 15 ** Auto Balanco 8~B 8et an~ Reset Comparators **
The purpose of the set comparator (U2A) is to provide a set pulse resulting from an increase in the pulse width from the "phase shift to pulse width conver-ter." A set pulse is defined as a continuous release, from common, of the set comparator's output for any duration of time. The set comparator will release its open collector output, whenever the DC level of the "medium" integrator is greater than the DC level of the "slow" integrator.
The purpose o~ the reset comparator (U2B) is to provide a "reset" pulse resulting from a decrease in the "phase shift of the pulse width converter's" pulse width.
A "reset" pulse is de~ined as a continuou3 pull to common of the reset comparator's output for any duration. The reset comparator will pull its open collector output to common, whenever the DC level of the "fast" integrator is less than the DC level of the "medium" integrator.
The "slow" integrator time preferably is set as slow as required, in order to maintain the required time constant differences between the integrators and minimize the ripple voltage of the "fast" integrator.
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The "medium" integrator time constant and voltage divider preferably is chosen to obtain a "set" pulse with a duration equal to the delay "on" time.
The "fast" integrator's time constant preferably is chosen to obtain a "recet" pulse upon the removal of a minimal input. A minimal input is defined as the smallest amount of impedance which could cause a set pulse.
Exemplary values for the "Integrators" block is set out below:
Component Valyç
Rl3 200Kn Rl~ looKn R15 looKn C4 l~F
C5 0.68~F
CC 0.047~F
** Constant Pressure 88B Level Deteotor **
The purpose of the level detector i8 to activate the button as long as the voltage on the integrator exceeds the fixed threshold. The integrator voltage being compared to a fixed threshold is what makes this a constant pressure ~CP) device.
Several factors contribute to the setting of the threshold set by the resistors R13 and R14. The thresh-old is set to allow for component tolerance variations within the specified working temperature range. The sensitivity of the button set by the threshold may be set to, for example, forty (40 pF) picofarads with nominal component values and should be no less than the pro~ected "worst case" scenario.
- ELECTRO8TATIC DI8CHARGB ~E8D) PROTECTION -The primary part of the electrostatic discharge (ESD) protection circuit is the spark gap 8Gl. In the event of an ESD the spark gap will activate and provide a low impedance path to earth via connector J4-l.
Connector J4-1 preferably is connected to the face plate of the button with a short wire. In hall .
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fixture applications the face plate should be connected to the masonry box with, for example, an insulated flat braided conductor. The masonry box in turn should be bonded to building steel through wiring conduit or a flat braided conductor to the closest building steel.
The spark gap is a relatively slow device, and, therefore, the zener diode CRl is used to limit any incoming voltage to, for example, thirty volts (30V).
The purpose of resistor Rl is to limit the current through the zener diode CR~ and absorb the major portion of the energy.
Resistor Rl may be selected to be of carbon composition due to their pulse energy handling capability and size. On the auto balance SSB the printed circuit (PC) board is conformably coated to prevent uncontrolled arching on the PC board during an ESD.
On the constant pressure SSB connector J4 may be a separate connector from Jl to maintain, for example, a quarter inch (0.25") spacing between the chassis ground and the rest of the circuit. The relatively large spacing is required to prevent uncontrolled arcing on the PC board during an ESD. During an ESD the potential of J4 will rise due to the very high frequency components of the ESD and the inductance of the chassis ground lead.
Appropriate spacing is also required ~rom the button connection to the button face. The electrical connectlon to the button face can be achieved with, for example, approprlate wlre soldered into the PC board and a ring terminal to the intermediate button stem or interconnecting bolt 7 (note F~g. 1), which bolt holds and electrically connects the button face and the PC
board.
- AUTO BAL~NCE 88B DE~AY ON TIME~ -In accordance with the invention the purpose of the delay on the timer is for erroneous signal rejection.
As generally discussed above, the erroneous signals of 2~2~
primary concern are those which could be caused by heat or other like eXtremQ environmental changes. Testing has shown that any set pulse~ caused by extreme environmental changes typically do not last longer than one hundred (100 msec.) milliseconds with an input resistance (R7) of, for example, one (1 Mn) megohms.
Further testing with the resistor R7 set to, for example, two hundred and sixty-one (261 kn) kilo-ohms resulted without any set pulses caused by extreme environmenta change. From these results a delay "on"
time of, for example, one hundred (100) milliseconds is deemed to be more than adequate for exemplary purposes.
The delay time may be achieved by a set pulse charging capacitor C8 through resistors R17, R18 and diode CR2 to a threshold set by resistors R20 and R21.
The voltage across capacitor C8 will reach the threshold, if a set pulse or series of set pulses transpire without the occurrence of any "reset" pulses.
once the threshold is reached, the output of comparator U2C is released from common. The voltage on capacitor C8 is pulled up and held high by hysteresis resistor R22, pending the occurrence of a "reset" pulse.
At any time the voltage across C8 can be quickly discharged by a "reset" pulse. The voltage across capacitor C~ is discharged through the current limiting resistor R19, which resets the timer.
- AUTO ~ALANCE 88~ DWE~L ON TIMER -The purpose Or the dwell "on" tlme is to insure that, once an input to the button face has activated the button, a call will be registered regardless of subse-guent changes to the input.
When the output of U2C is released from common, the capacitor C9 is quickly charged through R23 and CR3.
Once the voltage across the capacitor C9 reaches the "inactive" tkreshold, the output of comparator U2D is pulled to common. When the output of U2D is pulled to .. ~0 ..
~2~ j3 common, the button i3 activated. The threshold voltage to the non-inverting input of comparator U2D is set by resistors R2~ & R25 and the state of the output of U2D, which controls the hysteresis resistor R27.
The dwell "on" time begins when the input to the button face is removed, and, as a result, the output o~
~2C is pulled to common. The voltage across the capaci-tor C9 is discharged through resistor R26, providing the dwell "on" time. Once the voltage across the capacitor C9 reaches the "active" threshold, the output o~ compara-tor U2D is released from common, deactivating the output control.
Resistor R16 limits the discharge current to protect the output of UlC. Resistors R17 and R16 create a voltage divider to which capacitor C6 will discharge.
Re~istor R17 was selected to set the voltage of the divider lower than the "active" threshold voltage.
Diode CR7 protects Q6 by limiting the emitter to base voltage. When the output of comparator UlC is released and comparator UlD is pulled to common, a voltage divider is created by R17, CR7, and R19. This voltage divlder sets the voltage on the capacitor C6, while the button 1 is being held in the active state.
The difference between the voltage divider and the "active" threshold level provides the "dv" or di~ference in voltage ~or the dwell time.
Diode CR3 prevents leakage current through transistor Q6, which would decrease the delay on time provided by the charging o~ the capacitor C6.
- CON8TANT PRES8UR~ SSB DELAY/DWE~L TIMER -The delay/dwell of the CPSSB timer combines the purposes and functions o~ the ABSSB's delay and dwell timers.
The delay "on" time is initiated upon the release of the level detector's output from common, allowing capacitor C6 to charge through resistor R17. Once the 2 3 ~ e,; g voltage on C6 reaches the "inactive~' threshold the output o~ comparator UlD i8 pulled to common, activating the output control. The threshold voltage to the non-inverting ~nput of comparator UlD i8 set by resistors R20 & R21 and the state o~ the output o~ u2~ which controla the hysteresis resistor R22. The time required to charge C6 provides the delay "on" time.
If the input tot he button face is removed prior to the output of nlD being pulled to common the delay "on" time will be quickly reset. As a result of the input to the button face being removed the output of UlC
is pulled to common, providing a discharge path for C6 via CR3, Q6 and R16. Since the output of UlD is not pulled to sommon, transistor Q6 will be active during the discharge of capacitor C6. The activation of transistor Q6 effectively removes resistor R18 from the discharge path of C6, allowing the delay "on" time to be quickly reset.
The dwell "on" time begins when the input to the button face is removed after the output of UlD is pulled to common. ~he voltage across capacitor C6 i8 discharged through resistors R16 and R18, providing the dwell "on"
time. Once the voltage across C6 reaches the "active"
threshold the output of comparator U2D is released from common, deactivating the output control.
Resistor Rl6 limits the discharge current to protect the output of UlC. Resistors R17 & R16 create a voltage divider to which the capacitor C6 will discharge.
Re~i~tor R17 was selected to set the voltage of the divider lower than the "active" threshold voltage.
Diode CR7 protects transistor Q6 by limiting the emitter-to-base voltage. When the output of UlC is released and UlD is pulled to common, a voltage divider is created by resistor R17, diode CR7 and resistor Rl9.
This voltage divider sets the voltage on capacitor C6, while the button is being held in the active state. The 2~2~
difference between the voltage divider and the "actlve"
threshold level provides the "dv" for the dwell time.
Diode CR3 prevents leakage current through QC, which would decrease the delay "on" time provided by the charging of capacitor C6.
- O~TPUT CONTROL -The output control provides the active pull to common required by the "high out" and "illumination current regulator" functions.
Transistor Ql of the output control provides the signal inversion required between the output of compara-tor U2~ and the output driving transistor Q2.
Transistor Q2 was chosen to have the current rating required to drive the "high out" and "illumina-tion current regulator" functions.- HIGH OUT -The button assembly 10 is designed to interfaceto a remote station module in an elevator system. The output to the module is required to be an aative high level. The high level is provided through resistor R~0, when the transistor Q3 is driven into saturation by transistor Q2, pulling resistor R39 to common.
Resistor R40 is a current limiting resistor, which protects the transistor Q3 in the case of an accidental shorting of the output to ground.
- ILLUMINATION CURRENT R~CULATOR -The illumination i9 controlled by the button 1 through transistor Q2 or the module through connector Jl-2. The illumination is comprised, for example, of two external strings of LEDs being fed by dedicated current regulators through connectors J2 and J3. The current through each string is regulated to, for example, thirty (30mA) milliamps, by controlling the voltage across the resistors R~2 and R~3 with zener diode CR7.
The value of resistor R41 was selected to provide the proper current dependent voltage across diode CR7.
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The signal diode CRB is used to isolate the high level output ~rom the illumination control o~ the remote station module. This isolation allows the operational controller to be signaled, when the button i8 releaged.
Due to the minimum input voltage requirement of, for example, twenty and four-tenths volts DC (20.4 VDC) the nine light ring LEDs were divided into two strings.
- POWER UP AND CONTROL ~Y8TEM ~B~T PUNCTION8 -The power up reset insures that the button does not activate due to power outages of arbitrary duration.
Upon the application of power, capacitor C10 will charge at a rate set by the resistors R31 and R32 to a threshold set by resistors R33 and R3~. The output of comparator UlD is pulled to common, while the capacitor C10 is charging. The output o~ the comparator UlD being pulled to common prevents the capacitor C8 from charging, while the integrators charge to their steady state levels.
The purpose o~ diode CR~ is to quickly discharge the capacitor C10 in the event o~ short power outages.
A system reset is provided due to the remote possibility that noise could activate and latch the button 1. Under normal operation the button 1, when activated, will provide a high output to its remote station.
The operational control system will read in and acknowledge the call by turning on the appropriate remote station output. The output will pull the 'I/ILL W." input to common, turning "on" the illumination.
Once the elevator arrives at the ~loor, the control system typi¢ally will check the button output to see if a person is trying to hold the doors open with the call button. If the button output is active, the control system will hold the doors open and leave the button's illumination on. In the event the button is latched active or the person "fell asleep," the operational control system could remove its pull to common on the .
, 2~2~v~
"/ILL~M." input, turning the illumination "off" and providinq a reset.
When the ~/ILLUM." input is pulled to common, the bias across capacitor Cll is reversed. The capacitor Cll will discharge through diodes CR5 and CR6 and current limiting resistor R3C.
After discharging, the capacitor Cll will be charged to a voltage set by resistors R33 and R34. When the "/ILLUM." input pull to common is removed, the charge across the capacitor Cll will temporarily increase the voltage to the inverting input of comparator UlD. While the voltage of the non-inverting input is greater than the threshold set by resistors R31 and R32, the output of comparator UlD will be pulled to common discharging the capacitor C8.
Diode CR6 is used to prevent the voltage to the non-inverting input o~ the comparator ~lD from going too far below common, when the bias on the capacitor Cll i8 reversed.
Diode CR6 is used to prevent any current from ~lowing through resistor R35 from the "Illumination Current Regulator" function.
Diode CR9 i8 used to isolate the reset function from the Output Control.
Of course the circuits shown and described are exemplary and sub~ect to great variation. The specific values of each of the resistors, capacitors and diodes are not key to the invention and many workable values of them are available and known to those o~ ordinary skill.
The exemplary solid state button assembly de-scribed in detail above is designed to be applied in a hall fixture and car operating panel ~COP) of an eleva-tor, although, of course, many other uses and applica-tions are possible. The exemplary unit described is a ., , ,'" , ~ ; ' --~` 2~2~
low cost, easily replaceable device, taking, for example, flve (5) minutes to replace.
Although this invention has been shown and described with respect to detailed, exemplary embodiments thereof, it should be understood by those s~illed in the art that various changeR in form, detail, methodology and/or approach may be madQ without departing from the spirit and scope of this invention.
Having thus described two exemplary embodiments of the invention, that which is new and desired to be secured by Letters Patent is claimed below.
[OT-972]
Description CAPACITIV~ 8EN8IN~, 80 ~D 8TATB~TOUC~ BUTTON 8Y8T~M
Technical Fiel~
5The present invention relates to touch buttons typically used to activate or deactivate or otherwise control some electrical or electronic function, such as signaling, when touched typically by a human operator touching or "pushing" on the button with a finger. The invention more particularly relates to a solid state touch button system with no moving parts operated by capacitive sensing, which can be used in many different applications, including, for example, as a touch or push button for elevator car calling or control.
~ackground Art There is a need for a reliable button that does not use or need moving parts or mechanical contacts, to be used in, for example, elevator applications. It is desirable that such a button be aesthetically pleasing in appearance and use, highly reliable, low in cost and not be activated by extreme environmental changes.
It is known that the human body has some amount o~ capacitance to ground. A basic, previously known concept or approach i8 to monitor a button face for capacitance to ground, and, if a certain amount (or greater) capacitance is present, to activate the button.
In the present invention, this monitoring of the button surface is accomplished by monitoring the phase shift of a signal applied to the face of the button.
30However, due to the residual impedance of the button and the presence of external influences, the steady state phase shift of the button can fluctuate.
Such external influences include, for example, tempera-ture changes, cleaner residue build-up and other deposits , - ~ ~ 2 ~
or extreme environmental changes, etc. This fluctuation has the potential to falsely activate a button~ which is based on the monitoring of phase shift, although in fact no human operator is touching the button.
A distinguishing characteristic of such exemplary fluctuation is that it would occur slowly over a period of time relative to a phase shift induced by the presence of a person. To avoid this problem, in a first "auto-balancing" embodiment of the invention the steady state phase shift fluctuation is compensated for by 810wly auto balancing to all phase shifts. The rate of auto balance is set to be faster than the rate of change of the steady state phase shift. The rate of change of phase shifts induced by a person is faster than the auto balance rate, which allows the button to be operated. In a second, "constant pressure" embodiment, another way to compensate for the exemplary fluctuations is to simply set a threshold for activation higher than any normal fluctua-tions.
A second potential source of false activation~ of such a button are phase shifts induced by transient noise. These potential transients include, for example, electromagnetic interference (EMI) and radio frequency interference (RFI).
A distinguishing characteristic used in the invention to help prevent false activations caused by transient noise is that such noise would not last for a long period of time relative to the interaction time with a person. Activations due to transient noise thus are avoided in the invention by delaying the activation of the button for a certain minimum period of time.
Di~clo9ure o~ Invention Thus the present invention is directed to a reliable button that does not need, and preferably does ,' , ~ '-. . ' . : : , '. ;
:'~ .' . ' ' 2~2~
not use, any moving parts or mechanical contacts and can be used in, for example, elevator applications.
Additionally, the present invention i8 directed to a button that is aesthetically plea~ing in appearance and use, highly reliable, is low in cost and is not acti-vated by extreme environmental changes.
Finally and most importantly, the present inven-tion is directed to a phase shift monitoring, capacitive sensing button that avoids false activation of the button by residual impedance and external influences, such as temperature change, cleaner residue build-up and other deposits. The "auto-balancing" embodiment of the invention achieves this by compensating for them by slowly auto balancing to all such phase shifts, with the rate of auto balance being set to be faster than the rate of change of the steady state phase shift; while the "constant pressure" embodiment achieves it by compensat-ing for the exemplary fluctuations by simply setting a threshold for activation higher than any normal fluctua-tions. Additionally, the present invention avoids ~alseactivations by nolse transients, including those due to EMI and RFI by delaying the activation of the button, and the associated operative signal that causes it to be activated, by an appropriate amount of time, such as, for example, a time period of the order of about one hundred (100 msec.) milliseconds.
In the exemplary "auto balancing" embodiment, three integrators are used to provide the auto balancing feature o~ the invention. A "medium" speed lntegrator provides a "trigger" signal, while relatively "slow" and "fast" integrators provide "set" and "reset" thresholds.
In accordance with another aspect o~ the inven-tion, the purpose of the delay on the timer is for erroneous signal re~ection, as generally mentioned above.
The erroneous signals of primary concern are those which could be caused by extreme environmental changes.
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Testing has shown that any set pulses caused by exem-plary, extreme environmental changes typically do not last longer than one hundred (100 msec.) millisecond~
with an input resistance of, ~or example, one (l Mn) megohms.
Further testing with the input resistor set to, for example, two hundred and æixt~-one (261 kn) kilo-ohms resulted without any set pulses caused by extreme environmental conditions. From these results a delay "on" time of the order of about one hundred (loO) milliseconds is deemed to be appropriate.
In the exemplary "auto balance" embodiment the delay time is achieved by a set pulse charging a capaci-tor through resistors and a diode to a thre~hold set by other resistors. The voltage across the charging capaci-tor will reach the threshold, ~f a set pulse or series of set pulses transpire without the occurrence of any "reset" pulses.
once the threshold is reached, the output of a comparator is released from common. The voltage on the charging capacitor is pulled up and held high by a hysteresis resistor, pending the occurrence of a "reset"
pulse.
At any time the voltage across the charging capacitor can be quickly discharged by a "reset" pulse.
~ho volt~ge Aaro~ the ahArging capaaitor is discharged through a current llmiting resistor, which resets the timer.
Bene~its o~ the invention include the facts that the button is:
heat resistant;
EMI resistant;
RFI re~i~tant;
ESD resistant; and is capable of providing light and/or other feedback.
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The invention may be pr~cticed in a wide variety of applications, including but not restricted to, elevator car call or control buttons, utilizing known technology, in the light of the teachings of the inven-tion, which are discussed in detail hereafter.
Other ~eatures and advantages will be apparentfrom the specification and claims and from the accompany-ing drawings, which illustrate two exemplary embodiments of the invention, an auto-balancing embodiment and a constant pressure embodiment.
Brlof Desoription of ~raw~ng~
Figure 1 is an exploded, perspective view of an exemplary solid state push button, including the button, light ring, printed circuit (PC) board and holder ~or attaching the PC board to the push button elements and the overall button assembly to a face plate or panel, with the PC board carrying the electrical components which ~orm the exemplary electronics and circuitry of the present invention. (It is noted that the touch button elements of Pigur- 1 are basically symmetrical about their longitudinal center-line, except for the PC board and its associated holder.) Figuros 2A & 2B are interconnected schematic diagrams o~ an exemplary circuit for the button system of the present invention with auto balancing characteris-tics, with the two schematics being connected in the "Delay On Timer" block at the "SET/RESET" line; while Flgures 3a & 3~ are interconnected schematic diagrams o~ an alternate, exemplary circuit ~or the button system of the present invention with constant pressure characteristics, with the two schematics being connected in the "Delay~Dwell Timer" block at the "SET"
line.
2~23~c3~
ost ~es ~or C~rry~n~ U~_~he In~t~lon -- ~UTTON A8~MBLY ~10 ) As can be seen in F~gure 1, the exemplary "solid state button" (SSB) 10 of the present invention prefera-bly includes a non-moving, capacitive sensing button surface 1, that can be used, for example, as a call button in the car operating panel (COP) and/or hall fixtures of an elevator system. The SSB is capable of capacitively sensing a human touch, preferably providing lo both visual feed back (illumination) to the button pusher, as well as communication to the operational control of the elevator system through, for example, a remote station interface that the button has been actuated, so that the system accordingly can react.
The exemplary button o~ Figure 1 includes the non-moving button element 1 fitted within a light ring element 2, in which ring i9 carried a circular array of light emitting diodes (LEDs) 3 at its bottom. A printed circuit board ~, into which the light ring element 2 is pin inserted, is carried on the back side of the button elements 1, 2, and is held to the button elements by a bracket S and rear bolt 6.
The interconnecting bolt or stem 7 has a front, threaded, male end 7A, which is screwed into the back side of the button surfaca 1, and a rear, threaded, male end 7B, which is screwed into the ~ront end 6A of the rear bolt 6 with a lock washer 7C. The interconnecting bolt 7 extends through a center, circular opening ~unseen) in the light ring element 2 and through an opening in the PC board ~, while the head 6B of the rear bolt 6 fits into a notch in a "U" shaped rear strap 8, which i9 part of the bracket holder 5. When assembled, the intermediate elements of the button assembly 10 are held in compression between the button surface 1 and the head 6B of the bolt 6.
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The bracket 5 includes a series of peripherally spaced, lateral extensions 9 through which screw pins 9B
are placed for fastening the button assembly 10 to a face plate or panel. When so fastened, the only elements of the button assembly 10 which are seen by the user is the non-moving, circular button surface 1 surrounded by the translucent ring 2A, which is illuminated up by the internally contained LEDs when the button is actuated.
The printed circuit board 4 carries on it the electronic components and circuitry which perform the SSB monitoring functions of the present invention.
There are two basic exemplary embodiment~ of the present invention, a pure "constant pressure" solid state button (CPSSB) embodiment, schematically illus-trated in detail in Figures 3A & 3B, and a relatedpredecessor embodiment, the "auto balancing" solid state button (ABSSB), schematically illustrated in detail in Flgur~8 2A & 2B.
The primary difference between the "constant pressure" solid state button (CPSSB) and the "auto balancing" solid state button (ABSSB) is that the ABSSB
has an auto balancing feature. As generally noted above, the purpose of the auto balancing feature is to automat-ically accommodate for static changes in components, packaging and the environment, while maintaining a relatlvely high sensitivity to sensing when the button aetually has been aetuated. Due to the basic operation of auto balancing, the ABSSB is not a pure, "eonstant pressure" type button and, in the exemplary appliaation of an elevator system, iB not applied to, for example, "door open," "door close" and other applications requir-ing a pure constant pressure (CP) feature. In contrast the CPSSB module can be used, if desired, for all applications in the elevator system except the alarm button, which has special requirements.
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- T~EORY OF OP~ATION -If a button touch is constantly maintained ~or, for example, one hundred (100 msec.) milliseconds, the button module 10 will turn "on" its output and illumina-tion long enough to be read and controlled by theoperational control system without loss of the call or illumination. The illumination input preferably is controlled by the operational control system.
The ABSSB is reset upon the removal of the illumination control input. The illumination control of the CPSS8 can also be used as an output when applied to other systems.
- CIRCUI~ DE8CRIPTION -The basic functions for each embodiment (CPSSB &
ABSSB) are as follows:
Auto-Balance ~ABSSB) Constant Pressure (CPSSB) Power Power Oscillator Oscillator PhaseShiftToPulseWidth PhaseShiftToPulseWidth Converter Converter Integrators Integrators Set&Reset Comparators Level Detector Electrostatic Discharge Electrostatic Discharge (ESD) Protection (ESD) Protection Delay on Timer Delay/Dwell Timer Dwell on Timer Output Control Output Control High Out High Out Illumination Current Illumination Current Regulator Regulator PowerUp & Control System Reset Functions Figure~ 2A & 2B and 3A & 3B are schematics o~ the "auto balance~ embodiment and the "constant pressure~' embodiments, respectively, with these functions outlined in block form.
- POWER -~he power aspects of the two embodiments repre-sent standard approaches and their operation (and many :. :
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2~2~8 alternatives thereto) are known to thosé of ordinary skill.
- 08C~LLATOR -The oscillator generates, for example, a square wave of an appropriate cycle. The threshold voltage to the non-inverting input of comparator Ul~ is set by resistors R2 & R3, and the state of thè output of UlA, which controls the hysteresis resistor R~. The "on"
state threshold is higher than the "off" state threshold.
The oscillator i8 controlled by the charging and discharging of capacitor Cl. When comparator ~lA is in the "on" state, capacitor C1 will charge to the "on"
state threshold, and, as a result, the comparator will turn "off." Conversely, when comparator UlA is in the "off" state, capacitor Cl will discharge to the "off"
state threshold, and, as a result, the comparator will turn "on."
This is standard oscillator circuitry, and its operation and various alternatives are known to those of ordinary skill.
- P~A8E ~HIFT TO PUL~E WIDTH CONVERTER -** Auto B~l~nce 88B **
The phase shift to pulse width converter func-tions as follows. The oscillator is fed directly into the non-inverting input of UlC. When the oscillator is high, the output of UlC is released, providing the rising edge of the pulse. The inverting input of UlB monitors the phase shift o~ the oscillator through resistor R7 across the button input impedance. (The factors which contribute to the button input impedance are the capaci-tor C3, the ESD protection circuit and what is applied to or acquired by the button face.) When the voltage at the inverting input of U~B
reaches the threshold voltage on the non-inverting input, the output of UlB is pulled to common, at the falling edge of the pulse.
-- ` 2 ~ ~ ~ f c~ ~
There is always a pulse, even without anything applied to the button face 1. The pulse is due to the impedance of capacitor C3, the ESD protection circuit and any residuals in the circuit.
Capacitor c3 is u~ed to prevent any DC voltage from being placed on the button face. The value of the capacitor C3 should be significantly larger than the capacitive sensitivity to be obtained.
The larger the value of the resistor R7, the larger the phase shift is for a given input impedance, including the effects of resistance and noise. The value of the resistor R7 preferably is chosen to generate as large a phase shift as possible from the input.
** Constant Pres~ure 88B **
Functions on the CPSSB preferably are combined and condensed to reduce the number of required compo-nents. The function of UlC, R~5, and R46 in the "Phase Shift To Pulse Width Converter" block of the ABSSB can be condensed by, for example, replacing them with the diode CR2 on the CPSSB for its "Phase Shift To Pulse Width Converter" block. The functional performance of the pulse width to phase shift converter remains the same.
The integrators convert the pulse into a DC
voltage. The DC voltage i8 equal to the duty cycle of the pulse multiplied by "Vcc," the regulated supply voltage.
** Auto Balance 8~ **
The pulse from the "phase shift to pulse width converter" is fed into three different R-C integrators.
Each integrator has a different time constant, providing relatively "slow" ~R13 x C~), "medium" (R14//R16 x C5) and "fast" (R15 x C6) time constants. The "medium"
integrator has a resistor (R16) in parallel with its capacitor to act as a voltage divider. The voltage divider insures that the steady state DC voltage of the 21~2~ $
"medium" integrator will be less than that of the "slow"
and "fast lntegrators.
The three integrators of Figure 2A provide the auto balancing feature of the invention. The "medium"
S speed integrator provides the "trigger" signal, while the "slow" and "fast" integrators provide the "set" and "reset" thresholds.
The selection criteria for the integrator time constants is given below.
** Constant Pres~ure ~8~ **
In contrast, since the deletion of the auto balance feature is part of the purpose of the CPSSB, only one integrator is required for the CPSSB (F~g. 3A).
- 8ET AND RE8ET COMPARATOR8 AND ~VEL DETECTOR8 -- 15 ** Auto Balanco 8~B 8et an~ Reset Comparators **
The purpose of the set comparator (U2A) is to provide a set pulse resulting from an increase in the pulse width from the "phase shift to pulse width conver-ter." A set pulse is defined as a continuous release, from common, of the set comparator's output for any duration of time. The set comparator will release its open collector output, whenever the DC level of the "medium" integrator is greater than the DC level of the "slow" integrator.
The purpose o~ the reset comparator (U2B) is to provide a "reset" pulse resulting from a decrease in the "phase shift of the pulse width converter's" pulse width.
A "reset" pulse is de~ined as a continuou3 pull to common of the reset comparator's output for any duration. The reset comparator will pull its open collector output to common, whenever the DC level of the "fast" integrator is less than the DC level of the "medium" integrator.
The "slow" integrator time preferably is set as slow as required, in order to maintain the required time constant differences between the integrators and minimize the ripple voltage of the "fast" integrator.
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The "medium" integrator time constant and voltage divider preferably is chosen to obtain a "set" pulse with a duration equal to the delay "on" time.
The "fast" integrator's time constant preferably is chosen to obtain a "recet" pulse upon the removal of a minimal input. A minimal input is defined as the smallest amount of impedance which could cause a set pulse.
Exemplary values for the "Integrators" block is set out below:
Component Valyç
Rl3 200Kn Rl~ looKn R15 looKn C4 l~F
C5 0.68~F
CC 0.047~F
** Constant Pressure 88B Level Deteotor **
The purpose of the level detector i8 to activate the button as long as the voltage on the integrator exceeds the fixed threshold. The integrator voltage being compared to a fixed threshold is what makes this a constant pressure ~CP) device.
Several factors contribute to the setting of the threshold set by the resistors R13 and R14. The thresh-old is set to allow for component tolerance variations within the specified working temperature range. The sensitivity of the button set by the threshold may be set to, for example, forty (40 pF) picofarads with nominal component values and should be no less than the pro~ected "worst case" scenario.
- ELECTRO8TATIC DI8CHARGB ~E8D) PROTECTION -The primary part of the electrostatic discharge (ESD) protection circuit is the spark gap 8Gl. In the event of an ESD the spark gap will activate and provide a low impedance path to earth via connector J4-l.
Connector J4-1 preferably is connected to the face plate of the button with a short wire. In hall .
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fixture applications the face plate should be connected to the masonry box with, for example, an insulated flat braided conductor. The masonry box in turn should be bonded to building steel through wiring conduit or a flat braided conductor to the closest building steel.
The spark gap is a relatively slow device, and, therefore, the zener diode CRl is used to limit any incoming voltage to, for example, thirty volts (30V).
The purpose of resistor Rl is to limit the current through the zener diode CR~ and absorb the major portion of the energy.
Resistor Rl may be selected to be of carbon composition due to their pulse energy handling capability and size. On the auto balance SSB the printed circuit (PC) board is conformably coated to prevent uncontrolled arching on the PC board during an ESD.
On the constant pressure SSB connector J4 may be a separate connector from Jl to maintain, for example, a quarter inch (0.25") spacing between the chassis ground and the rest of the circuit. The relatively large spacing is required to prevent uncontrolled arcing on the PC board during an ESD. During an ESD the potential of J4 will rise due to the very high frequency components of the ESD and the inductance of the chassis ground lead.
Appropriate spacing is also required ~rom the button connection to the button face. The electrical connectlon to the button face can be achieved with, for example, approprlate wlre soldered into the PC board and a ring terminal to the intermediate button stem or interconnecting bolt 7 (note F~g. 1), which bolt holds and electrically connects the button face and the PC
board.
- AUTO BAL~NCE 88B DE~AY ON TIME~ -In accordance with the invention the purpose of the delay on the timer is for erroneous signal rejection.
As generally discussed above, the erroneous signals of 2~2~
primary concern are those which could be caused by heat or other like eXtremQ environmental changes. Testing has shown that any set pulse~ caused by extreme environmental changes typically do not last longer than one hundred (100 msec.) milliseconds with an input resistance (R7) of, for example, one (1 Mn) megohms.
Further testing with the resistor R7 set to, for example, two hundred and sixty-one (261 kn) kilo-ohms resulted without any set pulses caused by extreme environmenta change. From these results a delay "on"
time of, for example, one hundred (100) milliseconds is deemed to be more than adequate for exemplary purposes.
The delay time may be achieved by a set pulse charging capacitor C8 through resistors R17, R18 and diode CR2 to a threshold set by resistors R20 and R21.
The voltage across capacitor C8 will reach the threshold, if a set pulse or series of set pulses transpire without the occurrence of any "reset" pulses.
once the threshold is reached, the output of comparator U2C is released from common. The voltage on capacitor C8 is pulled up and held high by hysteresis resistor R22, pending the occurrence of a "reset" pulse.
At any time the voltage across C8 can be quickly discharged by a "reset" pulse. The voltage across capacitor C~ is discharged through the current limiting resistor R19, which resets the timer.
- AUTO ~ALANCE 88~ DWE~L ON TIMER -The purpose Or the dwell "on" tlme is to insure that, once an input to the button face has activated the button, a call will be registered regardless of subse-guent changes to the input.
When the output of U2C is released from common, the capacitor C9 is quickly charged through R23 and CR3.
Once the voltage across the capacitor C9 reaches the "inactive" tkreshold, the output of comparator U2D is pulled to common. When the output of U2D is pulled to .. ~0 ..
~2~ j3 common, the button i3 activated. The threshold voltage to the non-inverting input of comparator U2D is set by resistors R2~ & R25 and the state of the output of U2D, which controls the hysteresis resistor R27.
The dwell "on" time begins when the input to the button face is removed, and, as a result, the output o~
~2C is pulled to common. The voltage across the capaci-tor C9 is discharged through resistor R26, providing the dwell "on" time. Once the voltage across the capacitor C9 reaches the "active" threshold, the output o~ compara-tor U2D is released from common, deactivating the output control.
Resistor R16 limits the discharge current to protect the output of UlC. Resistors R17 and R16 create a voltage divider to which capacitor C6 will discharge.
Re~istor R17 was selected to set the voltage of the divider lower than the "active" threshold voltage.
Diode CR7 protects Q6 by limiting the emitter to base voltage. When the output of comparator UlC is released and comparator UlD is pulled to common, a voltage divider is created by R17, CR7, and R19. This voltage divlder sets the voltage on the capacitor C6, while the button 1 is being held in the active state.
The difference between the voltage divider and the "active" threshold level provides the "dv" or di~ference in voltage ~or the dwell time.
Diode CR3 prevents leakage current through transistor Q6, which would decrease the delay on time provided by the charging o~ the capacitor C6.
- CON8TANT PRES8UR~ SSB DELAY/DWE~L TIMER -The delay/dwell of the CPSSB timer combines the purposes and functions o~ the ABSSB's delay and dwell timers.
The delay "on" time is initiated upon the release of the level detector's output from common, allowing capacitor C6 to charge through resistor R17. Once the 2 3 ~ e,; g voltage on C6 reaches the "inactive~' threshold the output o~ comparator UlD i8 pulled to common, activating the output control. The threshold voltage to the non-inverting ~nput of comparator UlD i8 set by resistors R20 & R21 and the state o~ the output o~ u2~ which controla the hysteresis resistor R22. The time required to charge C6 provides the delay "on" time.
If the input tot he button face is removed prior to the output of nlD being pulled to common the delay "on" time will be quickly reset. As a result of the input to the button face being removed the output of UlC
is pulled to common, providing a discharge path for C6 via CR3, Q6 and R16. Since the output of UlD is not pulled to sommon, transistor Q6 will be active during the discharge of capacitor C6. The activation of transistor Q6 effectively removes resistor R18 from the discharge path of C6, allowing the delay "on" time to be quickly reset.
The dwell "on" time begins when the input to the button face is removed after the output of UlD is pulled to common. ~he voltage across capacitor C6 i8 discharged through resistors R16 and R18, providing the dwell "on"
time. Once the voltage across C6 reaches the "active"
threshold the output of comparator U2D is released from common, deactivating the output control.
Resistor Rl6 limits the discharge current to protect the output of UlC. Resistors R17 & R16 create a voltage divider to which the capacitor C6 will discharge.
Re~i~tor R17 was selected to set the voltage of the divider lower than the "active" threshold voltage.
Diode CR7 protects transistor Q6 by limiting the emitter-to-base voltage. When the output of UlC is released and UlD is pulled to common, a voltage divider is created by resistor R17, diode CR7 and resistor Rl9.
This voltage divider sets the voltage on capacitor C6, while the button is being held in the active state. The 2~2~
difference between the voltage divider and the "actlve"
threshold level provides the "dv" for the dwell time.
Diode CR3 prevents leakage current through QC, which would decrease the delay "on" time provided by the charging of capacitor C6.
- O~TPUT CONTROL -The output control provides the active pull to common required by the "high out" and "illumination current regulator" functions.
Transistor Ql of the output control provides the signal inversion required between the output of compara-tor U2~ and the output driving transistor Q2.
Transistor Q2 was chosen to have the current rating required to drive the "high out" and "illumina-tion current regulator" functions.- HIGH OUT -The button assembly 10 is designed to interfaceto a remote station module in an elevator system. The output to the module is required to be an aative high level. The high level is provided through resistor R~0, when the transistor Q3 is driven into saturation by transistor Q2, pulling resistor R39 to common.
Resistor R40 is a current limiting resistor, which protects the transistor Q3 in the case of an accidental shorting of the output to ground.
- ILLUMINATION CURRENT R~CULATOR -The illumination i9 controlled by the button 1 through transistor Q2 or the module through connector Jl-2. The illumination is comprised, for example, of two external strings of LEDs being fed by dedicated current regulators through connectors J2 and J3. The current through each string is regulated to, for example, thirty (30mA) milliamps, by controlling the voltage across the resistors R~2 and R~3 with zener diode CR7.
The value of resistor R41 was selected to provide the proper current dependent voltage across diode CR7.
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The signal diode CRB is used to isolate the high level output ~rom the illumination control o~ the remote station module. This isolation allows the operational controller to be signaled, when the button i8 releaged.
Due to the minimum input voltage requirement of, for example, twenty and four-tenths volts DC (20.4 VDC) the nine light ring LEDs were divided into two strings.
- POWER UP AND CONTROL ~Y8TEM ~B~T PUNCTION8 -The power up reset insures that the button does not activate due to power outages of arbitrary duration.
Upon the application of power, capacitor C10 will charge at a rate set by the resistors R31 and R32 to a threshold set by resistors R33 and R3~. The output of comparator UlD is pulled to common, while the capacitor C10 is charging. The output o~ the comparator UlD being pulled to common prevents the capacitor C8 from charging, while the integrators charge to their steady state levels.
The purpose o~ diode CR~ is to quickly discharge the capacitor C10 in the event o~ short power outages.
A system reset is provided due to the remote possibility that noise could activate and latch the button 1. Under normal operation the button 1, when activated, will provide a high output to its remote station.
The operational control system will read in and acknowledge the call by turning on the appropriate remote station output. The output will pull the 'I/ILL W." input to common, turning "on" the illumination.
Once the elevator arrives at the ~loor, the control system typi¢ally will check the button output to see if a person is trying to hold the doors open with the call button. If the button output is active, the control system will hold the doors open and leave the button's illumination on. In the event the button is latched active or the person "fell asleep," the operational control system could remove its pull to common on the .
, 2~2~v~
"/ILL~M." input, turning the illumination "off" and providinq a reset.
When the ~/ILLUM." input is pulled to common, the bias across capacitor Cll is reversed. The capacitor Cll will discharge through diodes CR5 and CR6 and current limiting resistor R3C.
After discharging, the capacitor Cll will be charged to a voltage set by resistors R33 and R34. When the "/ILLUM." input pull to common is removed, the charge across the capacitor Cll will temporarily increase the voltage to the inverting input of comparator UlD. While the voltage of the non-inverting input is greater than the threshold set by resistors R31 and R32, the output of comparator UlD will be pulled to common discharging the capacitor C8.
Diode CR6 is used to prevent the voltage to the non-inverting input o~ the comparator ~lD from going too far below common, when the bias on the capacitor Cll i8 reversed.
Diode CR6 is used to prevent any current from ~lowing through resistor R35 from the "Illumination Current Regulator" function.
Diode CR9 i8 used to isolate the reset function from the Output Control.
Of course the circuits shown and described are exemplary and sub~ect to great variation. The specific values of each of the resistors, capacitors and diodes are not key to the invention and many workable values of them are available and known to those o~ ordinary skill.
The exemplary solid state button assembly de-scribed in detail above is designed to be applied in a hall fixture and car operating panel ~COP) of an eleva-tor, although, of course, many other uses and applica-tions are possible. The exemplary unit described is a ., , ,'" , ~ ; ' --~` 2~2~
low cost, easily replaceable device, taking, for example, flve (5) minutes to replace.
Although this invention has been shown and described with respect to detailed, exemplary embodiments thereof, it should be understood by those s~illed in the art that various changeR in form, detail, methodology and/or approach may be madQ without departing from the spirit and scope of this invention.
Having thus described two exemplary embodiments of the invention, that which is new and desired to be secured by Letters Patent is claimed below.
Claims (7)
1. A capacitive sensing touch button for controlling a function, said button comprising:
a button surface for receiving a reference signal, said button surface outputting a signal shifted in phase, relative to the reference signal, upon contact of said button surface by a user, an oscillator, operatively connected to said button surface, to provide the reference signal to said button surface, said oscillator having a predetermined duty cycle;
phase shift to pulse width converter, operatively connected to said button surface and said oscillator, to convert the phase-shifted signal into a pulse width based on the amount of the phase shift relative to the reference signal;
auto-balancing compensation, operatively connected to said phase shift to pulse width converter, including at least two integrators, each having a different time constant, each of said integrators receiving the pulse width and converting the pulse width into a dc voltage, said auto-balancing compensation outputting either a SET signal or a RESET
signal based on the relative dc voltage values produced by said integrators, thereby avoiding false activation of the controlled function due to residual impedence and/or external influences at said button surface; and delay-on circuitry, operatively connected to said auto-balancing compensation, to receive the signal output therefrom, said delay-on circuitry generating a control signal to control the controlled function provided that said SET signal is present at least a predetermined time period, thereby avoiding false activation of the controlled function due to transient noise.
a button surface for receiving a reference signal, said button surface outputting a signal shifted in phase, relative to the reference signal, upon contact of said button surface by a user, an oscillator, operatively connected to said button surface, to provide the reference signal to said button surface, said oscillator having a predetermined duty cycle;
phase shift to pulse width converter, operatively connected to said button surface and said oscillator, to convert the phase-shifted signal into a pulse width based on the amount of the phase shift relative to the reference signal;
auto-balancing compensation, operatively connected to said phase shift to pulse width converter, including at least two integrators, each having a different time constant, each of said integrators receiving the pulse width and converting the pulse width into a dc voltage, said auto-balancing compensation outputting either a SET signal or a RESET
signal based on the relative dc voltage values produced by said integrators, thereby avoiding false activation of the controlled function due to residual impedence and/or external influences at said button surface; and delay-on circuitry, operatively connected to said auto-balancing compensation, to receive the signal output therefrom, said delay-on circuitry generating a control signal to control the controlled function provided that said SET signal is present at least a predetermined time period, thereby avoiding false activation of the controlled function due to transient noise.
2. The capacitive sensing touch button of claim 1, wherein:
said auto-balancing compensation includes three integrators, a first integrator having a relatively slow time constant, a third integrator having a relatively fast time constant, and a second integrator having a time constant between the first and second time constants, each of said integrators receiving the pulse width and converting the pulse width into a dc voltage;
said auto-balancing compensation outputting the SET signal when the voltage output from said second integrator is greater than the voltage output from said first integrator; and said auto-balancing compensation outputting the RESET signal when the voltage output from said third integrator is less than the voltage output from said second integrator.
said auto-balancing compensation includes three integrators, a first integrator having a relatively slow time constant, a third integrator having a relatively fast time constant, and a second integrator having a time constant between the first and second time constants, each of said integrators receiving the pulse width and converting the pulse width into a dc voltage;
said auto-balancing compensation outputting the SET signal when the voltage output from said second integrator is greater than the voltage output from said first integrator; and said auto-balancing compensation outputting the RESET signal when the voltage output from said third integrator is less than the voltage output from said second integrator.
3. The capacitive sensing touch button of claim 1, said touch button further including electrostatic discharge protection circuitry operatively connected between said button surface and said phase shift to pulse width converter, said protection circuitry comprising:
a spark gap connected between said button surface and a first grounding path;
a resistor having a first terminal connected to said button surface and a secondterminal connected to said phase shift to pulse width converter, and a Zener diode connected between said second terminal of said resistor and a second grounding path, wherein said first and said second grounding paths are separate.
a spark gap connected between said button surface and a first grounding path;
a resistor having a first terminal connected to said button surface and a secondterminal connected to said phase shift to pulse width converter, and a Zener diode connected between said second terminal of said resistor and a second grounding path, wherein said first and said second grounding paths are separate.
4. A capacitive sensing touch button for controlling a function, said button comprising:
a button surface for receiving a reference signal, said button surface outputting a signal shifted in phase, relative to the reference signal upon contact of said button surface by a user;
an oscillator to provide the reference signal to said button surface, said oscillator having a predetermined duty cycle;
phase shift to pulse width converter to convert the phase-shifted signal into a pulse width based on the amount of the phase shift relative to the reference signal;
an integrator to convert the pulse width into a dc voltage;
a level detector to output a control signal when the dc voltage is greater than a predetermined threshold voltage; and a delay/dwell timer to receive said control signal and to control the controlledfunction provided that said control signal is present at least a predetermined time period, thereby avoiding false activation of the controlled function due to transient noise.
a button surface for receiving a reference signal, said button surface outputting a signal shifted in phase, relative to the reference signal upon contact of said button surface by a user;
an oscillator to provide the reference signal to said button surface, said oscillator having a predetermined duty cycle;
phase shift to pulse width converter to convert the phase-shifted signal into a pulse width based on the amount of the phase shift relative to the reference signal;
an integrator to convert the pulse width into a dc voltage;
a level detector to output a control signal when the dc voltage is greater than a predetermined threshold voltage; and a delay/dwell timer to receive said control signal and to control the controlledfunction provided that said control signal is present at least a predetermined time period, thereby avoiding false activation of the controlled function due to transient noise.
5. The capacitive sensing touch button of claim 4, said touch button further including electrostatic discharge protection circuitry operatively connected between said button surface and said phase shift to pulse width converter, said protection circuitry comprising:
a spark gap connected between said button surface and a first grounding path;
a resistor having a first terminal connected to said button surface and a secondterminal connected to said phase shift to pulse width converter; and a Zener diode connected between said second terminal of said resistor and a second grounding path, wherein said first and said second grounding paths are separate.
a spark gap connected between said button surface and a first grounding path;
a resistor having a first terminal connected to said button surface and a secondterminal connected to said phase shift to pulse width converter; and a Zener diode connected between said second terminal of said resistor and a second grounding path, wherein said first and said second grounding paths are separate.
6. The capacitive sensing touch button of claim 4, wherein said phase shift to pulse width converter comprises a diode.
7. The capacitive sensing touch button of claim 4, wherein said delay/dwell timer comprises:
a transistor having an emitter operatively connected to said control signal;
a first resistor and first diode in series connection between said emitter and the collector of said transistor, wherein said first diode's cathode is connected to said collector;
a second diode having an anode and a cathode operatively connected between said emitter and the base, respectively, of said transistor; and a comparator having a first input operatively connected to said anode of said first diode, said first input further operatively connected ground via a first capacitor, and a second input operatively connected to an RC network having a predetermined time constant, wherein the output of said comparator controls the controlled function, provided that said control signal is present at least a predetermined time period, wherein said predetermined time period is based on said time constant.
a transistor having an emitter operatively connected to said control signal;
a first resistor and first diode in series connection between said emitter and the collector of said transistor, wherein said first diode's cathode is connected to said collector;
a second diode having an anode and a cathode operatively connected between said emitter and the base, respectively, of said transistor; and a comparator having a first input operatively connected to said anode of said first diode, said first input further operatively connected ground via a first capacitor, and a second input operatively connected to an RC network having a predetermined time constant, wherein the output of said comparator controls the controlled function, provided that said control signal is present at least a predetermined time period, wherein said predetermined time period is based on said time constant.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US401,363 | 1989-08-31 | ||
| US07/401,363 US5036321A (en) | 1989-08-31 | 1989-08-31 | Capacitive sensing, solid state touch button system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2023958A1 CA2023958A1 (en) | 1991-03-01 |
| CA2023958C true CA2023958C (en) | 1994-04-19 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002023958A Expired - Fee Related CA2023958C (en) | 1989-08-31 | 1990-08-24 | Capacitive sensing, solid state touch button system |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US5036321A (en) |
| EP (2) | EP0717499A3 (en) |
| JP (2) | JP3150329B2 (en) |
| CN (1) | CN1019872B (en) |
| AU (1) | AU620260B2 (en) |
| BR (1) | BR9004320A (en) |
| CA (1) | CA2023958C (en) |
| DE (1) | DE69029296T2 (en) |
| HK (1) | HK1001709A1 (en) |
| RU (1) | RU2067354C1 (en) |
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| CA2073676A1 (en) * | 1990-01-11 | 1991-07-12 | York Liao | Touch sensing device |
-
1989
- 1989-08-31 US US07/401,363 patent/US5036321A/en not_active Expired - Fee Related
-
1990
- 1990-08-24 CA CA002023958A patent/CA2023958C/en not_active Expired - Fee Related
- 1990-08-24 AU AU61355/90A patent/AU620260B2/en not_active Ceased
- 1990-08-30 RU SU904830904A patent/RU2067354C1/en active
- 1990-08-30 BR BR909004320A patent/BR9004320A/en not_active Application Discontinuation
- 1990-08-31 EP EP96101017A patent/EP0717499A3/en not_active Withdrawn
- 1990-08-31 EP EP90309565A patent/EP0415789B1/en not_active Expired - Lifetime
- 1990-08-31 JP JP23231090A patent/JP3150329B2/en not_active Expired - Fee Related
- 1990-08-31 CN CN90107444A patent/CN1019872B/en not_active Expired
- 1990-08-31 DE DE69029296T patent/DE69029296T2/en not_active Expired - Fee Related
-
1998
- 1998-01-26 HK HK98100672A patent/HK1001709A1/en not_active IP Right Cessation
-
2000
- 2000-10-23 JP JP2000322112A patent/JP2001168703A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| RU2067354C1 (en) | 1996-09-27 |
| JP2001168703A (en) | 2001-06-22 |
| JP3150329B2 (en) | 2001-03-26 |
| EP0717499A2 (en) | 1996-06-19 |
| DE69029296D1 (en) | 1997-01-16 |
| BR9004320A (en) | 1991-09-03 |
| CN1019872B (en) | 1992-12-30 |
| EP0415789A3 (en) | 1992-03-25 |
| JPH03166820A (en) | 1991-07-18 |
| EP0717499A3 (en) | 1998-01-07 |
| AU620260B2 (en) | 1992-02-13 |
| CN1049944A (en) | 1991-03-13 |
| CA2023958A1 (en) | 1991-03-01 |
| HK1001709A1 (en) | 1998-07-03 |
| EP0415789A2 (en) | 1991-03-06 |
| AU6135590A (en) | 1991-03-07 |
| EP0415789B1 (en) | 1996-12-04 |
| US5036321A (en) | 1991-07-30 |
| DE69029296T2 (en) | 1997-06-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |