United States Patent [19J
`Roudeski
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,764,708
`Aug. 16, 1988
`
`[54] TOUCH CONTROL LAMP SOCKET
`INTERIOR
`
`[76]
`
`Inventor: Charles A. Roudeski, 97 Willow
`Wood Cir., Urbana, Ohio 43078
`
`[21] Appl. No.: 938,827
`
`[22] Filed:
`
`Dec. 8, 1986
`
`[51]
`
`Int. Cl.4 ......................... H01J 7/44; HOlJ 19/28;
`HOlJ 29/96; HOlJ 17/34
`[52] U.S. CI ......................................... 315/51; 315/53;
`315/72; 315/149; 315/362; 315/DIG.4;
`307/116; 307/125; 307/157; 307/308;
`200/DIG.1
`[58] Field of Search ............... 307/116, 125, 157, 308,
`307/247 R; 200/DIG. 1; 315/362, 74, 72, DIG.
`4, 227 R, 51, 53, 149, 194
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`2,206,217 7/1940 Barry ................................... 315/362
`2,953,769 9/1960 Woofter eta! ........... 315/DIG. 4 X
`3,165,371
`l/1965 Ruocco ............................... 313/318
`3,300,711
`l/1967 Duncan ................................. 339/78
`3,543,088 11/1970 Garrett ................................ 315/272
`3,896,334 7/1975 Rodriquez ........................... 315/194
`4,101,805 7/1978 Stone ..................................... 315/74
`4,183,604 1/1980 Tjomhom, Sr ....................... 315/72
`4,211,959 7/1980 Deavenport et al. ............... 315/362
`4,237,386 12/1980 Instance .............................. 307/116
`4,250,432 2/1981 Koehler .............................. 315/291
`4,490,625 12/1984 Dilly .................................... 307/116
`4,613,790 9/1986 Roorda ................................. 315/72
`4,668,887 5/1987 Kunen ................................. 307/116
`
`Primary Examiner-David K. Moore
`Assistant Examiner-Mark R. Powell
`Attorney, Agent, or Firm-Killworth, Gottman, Hagan
`& Schaeff
`[57]
`ABSTRACT
`An electric touch control light socket used to convert a
`lamp to touch-sensitive use .which includes a circuit
`housing and a light bulb insertion socket mounted
`thereto which together are adapted for installation
`within a standard light socket shell of a lamp in place of
`a standard light socket. A touch sensing circuit in the
`circuit housing has a self-compensating subcircuit to
`eliminate the effects of slower changing ambient capaci(cid:173)
`tance of the lamp in order to detect touching of the
`lamp by monitoring rapid changes in lamp capacitance.
`A spring contact connected to the circuit is attached to
`the circuit housing and projects along a side thereof for
`placement between the circuit housing exterior and the
`interior surface of the light socket shell and in electrical
`contact with a conductive portion of the light socket
`shell when the circuit housing and insertion socket are
`installed within the light socket shell. The spring
`contact thereby is inaccessible from the exterior of the
`lamp and is adapted to convey to the circuit an electri(cid:173)
`cal touch-responsive input signal generated when a
`person touches a conductive exterior portion of the
`lamp connected to the conductive portion of the light
`socket shell. The circuit has an operating mode control
`subcircuit actuable by a manually-operable control
`knob for selecting the operating mode of the circuit, e.g.
`ON/OFF, 4-Level, or 5-Level dimmer sequences.
`
`18 Claims, 4 Drawing Sheets
`
`MICROSOFT EXHIBIT 1009
`
`

`

`U.S. Patent
`US. Patent
`
`Aug. 16, 1988
`Aug.16, 1988
`
`Sheet 1 of4
`Sheet 1 of 4
`
`4,764,708
`4,764,708
`
`FIG-I
`
`
`
`

`

`U.S. Patent Aug.t6, 1988
`US. Patent
`F/G-2
`
`Sheet 2 of 4
`
`4,764,708
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`

`

`U.S. Patent Aug. 16, 1988
`US. Patent
`Aug. 16,1988
`
`Sheet 3 of4
`Sheet 3 of 4
`
`4,764,708
`4,764,708
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`

`

`1
`
`4,764,708
`
`TOUCH CONTROL LAMP SOCKET INTERIOR
`
`20
`
`BACKGROUND OF THE INVENTION
`The present invention generally relates to conversion 5
`of a lamp to touch control and, more particularly, to an
`electronic touch control light socket for conversion of
`ordinary lamps, such as a table lamp, to touch control
`which installs directly in the lamp in place of an ordi(cid:173)
`nary light socket, and is "wireless" in the sense that the 10
`device eliminates all wiring related to touch control
`conversion.
`'
`Touch control lamps, both on/off and dimming
`types, have grown in popularity over the years, offering
`solid-state control of the lamp with a touch of the 15
`lamp's metallized body parts. Touch controls are quick
`and convenient, and especially ideal for pre-schoolers
`and physically disabled persons, such as arthritics, who
`find it difficult, in view of their limited dexterity, to
`operate conventional light switches.
`One prior art approach for converting a table lamp to
`touch control, such as disclosed in U.S. Pat. No.
`4,237,386 to Instance, is to package the touch control
`circuit in a separate, bulky module. The module can be
`applied to either a wall socket or mounted on the base of 25
`the lamp. Base mounting, however, embodies several
`disadvantages. It requires several wire connections to
`provide power to and from the module, as well as a
`connection to the lamp body to convey the lamp's
`touch signal to the touch-sensitive circuit. Moreover, 30
`these connections add assembly time to the lamp, and
`the wire splices used can be a hazard, particularly with
`all-metal lamp bodies. Furthermore, repair and replace(cid:173)
`ment of the touch module can also be difficult and ex(cid:173)
`pensive, requiring disassembly or removal of the lamp 35
`base to gain access to the module. In addition, the mod(cid:173)
`ules' large size and wiring has often made installation in
`small lamps, solid-body lamps, and transparent lamps
`impractical or impossible due to lamp size or styling
`constraints.
`A more recent approach for converting a table lamp
`to touch control has been to provide a touch control
`adapter which screws into the existing light socket,
`between the light bulb and its socket. Typically, a single
`clip-on wire or external spring is used to contact the 45
`shade support (harp) or outer surface of the light socket
`housing (shell) to couple the touch signal to the adapt(cid:173)
`er's circuit. This approach is primarily intended for the
`do-it-yourselfer, whereby the user can convert existing
`table lamps to touch control use. However, adapters 50
`add inches to the height of the light bulb thereby inter(cid:173)
`fering with many short-harp designs or globe shades
`which require the lamp's filament to be centered for
`even light distribution. Furthermore, the adapter's clip-
`on wire may be disturbed by unfamiliar users who at- 55
`tempt to turn on the lamp in a conventional manner.
`Lamp manufacturers view the adapter as an after-mar(cid:173)
`ket add-on, not intended for lamp manufacturing use,
`which is expensive, i.e. adding the cost of male and
`female screw-in threads in addition to the cost of an 60
`already costly touch control circuit.
`Consequently, a need still remains for a fresh ap(cid:173)
`proach to converting a lamp, such as an ordinary table
`lamp, to touch control. The objective of such an ap(cid:173)
`proach should be to avoid the drawbacks and shortcom- 65
`ings of the above-described prior art approaches with(cid:173)
`out introducing new ones in their place. Also, such an
`approach should seek to have substantially universal
`
`40
`
`2
`applicability to all types of lamps and require minimal
`skill on the part of the installer in converting the lamp to
`touch control.
`
`SUMMARY OF THE INVENTION
`The present invention provides an electronic touch
`control light socket designed to satisfy the aforemen(cid:173)
`tioned long-felt needs. The touch control socket con(cid:173)
`verts ordinary lamps, such as a table lamp, to touch
`control use which installs directly in the lamp in place
`of an ordinary light socket, and is "wireless" in the
`sense that the device eliminates all wiring related to
`touch control conversion. Therefore, a separate bulky
`module is eliminated and the position of the light bulb
`within the lamp remains unchanged, The touch control
`socket includes a touch-sensitive electrical circuit hav(cid:173)
`ing a self-compensating capacitance subcircuit which
`detects touches by monitoring changes in lamp capaci(cid:173)
`tance, making the device compatible with virtually any
`lamp design. Also, in place of the conventional push(cid:173)
`button or rotatable on/off switch, a rotatable control
`knob can be incorporated into the touch control socket
`to select its desired operating mode, such as an on/off
`dim level or one of several dimmer sequencing modes.
`The present invention is thus directed to a touch
`control light socket for converting a lamp to touch-sen(cid:173)
`sitive operation, wherein the device includes a noncon(cid:173)
`ductive circuit housing and a conductive light bulb
`insertion socket mounted on the circuit housing in over(cid:173)
`lying relation thereto. The circuit housing and insertion
`socket together are adapted for installation within a
`standard light socket shell in place of a standard light
`socket. The device also includes a touch sensing electri(cid:173)
`cal circuit disposed in the circuit housing and having
`conductive means being adapted for electrical connec(cid:173)
`tion to the a.c. supply conductors of the lamp. The
`circuit is adapted to control a light bulb inserted into the
`insertion socket of the device upon receipt of a touch(cid:173)
`responsive electrical input signal. Further, the device
`includes conductive contact means electrically con(cid:173)
`nected to the circuit and being electrically coupled to a
`conductive exterior portion of the lamp when the cir(cid:173)
`cuit housing and insertion socket are installed within the
`light socket shell. In such manner, the contact means is
`adapted to convey to the circuit the touch-responsive
`electrical input signal generated when a person touches
`the conductive exterior portion of the lamp.
`More particularly, the conductive contact is attached
`to the circuit housing so as to project from the exterior
`thereof such that the contact is capable of being dis(cid:173)
`posed between the exterior of the circuit housing and
`the interior surface of the light socket shell and in elec(cid:173)
`trical contact with a conductive portion of the light
`socket shell when the circuit housing and insertion
`socket are installed within the light socket shell. The
`conductive contact is thereby inaccessible from the
`exterior of the lamp and adapted to convey to the cir(cid:173)
`cuit an electrical touch-responsive signal generated
`when a person touches a conductive exterior portion of
`the lamp being electrically connected to the conductive
`portion of the light socket shell. In one form, the con(cid:173)
`ductive contact is a contact spring. The conductive
`means of the circuit for power is in the form of a pair of
`electrical terminals defined on the exterior of the circuit
`housing and adapted for connection to the a.c. supply
`conductors of the lamp. The terminals are located on
`opposite sides of the circuit housing and are displaced
`
`

`

`4,764,708
`
`3
`about the housing away from the location of the con(cid:173)
`ductive contact spring.
`Still further, the touch sensing electrical circuit of the
`device includes an a.c. switching device, a capacitance
`detection and compensation subcircuit, level detection 5
`means, and an operating mode control subcircuit. The
`a.c. switching device is electrically connected in series
`with the light bulb of the lamp when inserted into the
`insertion socket of the device and has bi-directional
`conducting and nonconducting states wherein the bulb 10
`is respectively turned "on" and "off' during the a.c.
`voltage half-cycle to control lamp intensity. The capaci(cid:173)
`tance detection and compensation subcircuit is electri(cid:173)
`cally connected to the conductive contact for detecting
`a touch-responsive signal by monitoring changes in 15
`lamp capacitance conveyed thereto via the conductive
`contact. The detection and compensation subcircuit has
`a fast-responding touch-sensitive capacitance circuit
`portion and a slow-responding ambient-sensitive capac(cid:173)
`itance circuit portion which produce opposing-polarity 20
`signals which vary in response to changes in lamp ca(cid:173)
`pacitance. The level detection means is connected to
`the capacitance detection and compensation subcircuit
`for receiving the opposing-polarity signals therefrom
`and summing the same for producing a compensated 25
`detection signal wherein the effects of varying ambient
`conditions have been substantially eliminated and the
`magnitude thereof is either less than a predetermined
`voltage level which represents nondetection of the
`touch-responsive input signal or equal to or greater than 30
`the predetermined voltage level which represents de(cid:173)
`tection of the touch-responsive input signal. The com(cid:173)
`pensated detection signal, when less than the predeter(cid:173)
`mined level and applied to the level detection means,
`causes the detector output to remain "ofr'; whereas the 35
`signal, when at or greater than the predetermined level
`and applied to the level detector, causes the detector
`output to tum "on".
`The operating mode control subcircuit is electrically
`connected to the a.c. switching device and the level 40
`detection means and provides selectable dimmer se(cid:173)
`quencing modes as required. The operating mode con(cid:173)
`trol subcircuit receives the changing output signal from
`the level detection means and steps the mode control
`dimming logic to the next control state in response to 45
`each change of the compensated signal from below to
`above the predetermined level. The mode of the operat(cid:173)
`ing mode control subcircuit is selectable for ON/OFF,
`4-Level, or 5-Level dimmer sequencing by a manually(cid:173)
`operable control knob extending from the circuit hous- 50
`ing and through an opening in the standard light socket
`shell previously occupied by a standard light switch of
`the standard light socket. The control knob is disposed
`adjacent to and above the conductive contact on the
`circuit housing.
`Accordingly, it is an object of the present invention
`to provide a touch control light socket having a circuit
`housing with a light bulb insertion socket attached
`thereto which both can replace the standard light
`socket of a lamp in converting the lamp to touch con- 60
`trol; to provide a conductive contact on the circuit
`housing which projects therefrom to electrically couple
`with the lamp exterior when the circuit housing and
`insertion socket are disposed inside the light socket shell
`of the lamp; to provide the conductive contact between 65
`the circuit housing and the light socket shell such that
`the conductive contact is completely hidden and inac(cid:173)
`cessible from the exterior of the lamp; to provide a
`
`55
`
`4
`touch-sensitive circuit in the circuit housing having a
`capacitance detection and compensation subcircuit
`which, in sensing a touch-responsive electrical signal,
`automatically compensates for changes in lamp capaci(cid:173)
`tance as a result of varying ambient conditions; to pro(cid:173)
`vide circuit terminals on the circuit housing which are
`displaced away from the conductive contact thereon;
`and to provide an operating mode control subcircuit in
`the touch-sensitive circuit with a control knob which
`extends from the circuit housing and through the light
`socket shell of the lamp in place of an on/off push-but(cid:173)
`ton.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematical representation of a table lamp
`having the touch control light socket of the present
`invention installed in the lamp;
`FIG. 2 is an enlarged elevational view, partly in sec(cid:173)
`tion, of the device mounted inside the light socket shell
`of the lamp of FIG. 1;
`FIG. 3 is a side elevational view, partly in section, of
`the device by itself;
`FIG. 4 is another side elevational view, partly in
`section, of the device rotated ninety-degrees clockwise
`from its position in FIG. 3 about a vertical axis; and
`FIG. 5 is a schematic diagram of the device showing
`the touch sensing electrical circuit.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`Referring to FIGS. 1 and 2 of the drawings, there is
`illustrated a typical table lamp 10 with a preferred em(cid:173)
`bodiment of the touch control light socket 12 of the
`present invention installed in the lamp 10 in place of a
`conventional light socket. The table lamp 10 conven~
`tionally has a body 14 supported upright on a base 16
`which rests on a support surface, such as a table (not
`shown). An a.c. supply conductor cord 18 typically has
`a polarized plug 20 on one end which inserts into an
`electrical outlet (not shown). To convert the lamp 10 to
`touch-sensitive control operation, the touch control
`light socket 12 is installed inside the light socket's shell
`22. The a.c. supply conductor cord 18 typically runs
`upwardly through a central pipe 24 in the lamp body 14
`and connects at its opposite end to the touch control
`light socket 12.
`The light socket shell 22 of the lamp 10 includes a
`shell base 26 attached to the upper end of the lamp body
`14 and a shell body 28 disposed at its lower end in the
`shell base 26 and retained therein by crimps 30 which
`snap into openings 32 in the lower end of the shell body
`28. A tubular liner 34 of a nonconductive material such
`as cardboard is inserted into the shell 22 and has an
`elongated opening 36 cut therein which ordinarily al(cid:173)
`lows extension of an on/off light switch (not shown)
`therethrough for access by a user. The light switch
`normally part of the light socket (not shown), is now
`replaced by the touch control socket 12.
`Thus, the touch control light socket 12, sized to be
`compatible with most standard light socket shells, takes
`the place previously occupied by a conventional light
`socket within the socket shell 22 of the lamp :1.0. As best
`seen in FIGS. 3 and 4, the device 12 includes an electri(cid:173)
`cally nonconductive circuit housing 38, fabricated of
`any suitable heat-resistant plastic, and a light bulb
`screw-in or insertion socket 40 attached to the top of the
`circuit housing 38, such as by rivets 42. Therefore, it is
`the circuit housing 38 and the insertion socket 40 to-
`
`

`

`5
`gether which are installed within the light socket shell
`22 of the lamp 10 in place of its conventional light
`socket.
`The touch control light socket 12 further includes a
`touch-sensing electrical circuit 44 (of FIG. 5), prefera- 5
`bly formed on a circuit board 45 and mounted within
`and across the lower portion of the circuit housing 38.
`In such location, the circuit 44 is displaced as far as
`possible away from the heat produced by the light bulb
`in the insertion socket 40 of the device 12. A bottom 10
`cover 46 fits within and closes the lower end of the
`circuit housing 38. A pair of electrical screw terminals
`48A,48B are threadably mounted and fit into the circuit
`housing 38 with the heads 50 thereof disposed within
`recessed or cutout regions 52 defmed on the housing 15
`exterior so that the terminal heads 50 will not interfere
`with installation of the circuit housing 38 within the
`light socket shell 22. The threaded ends 54 of the screw
`terminals 48A,48B are electrically connected to the
`circuit 44, whereas the heads 50 are electrically con- 20
`nected respectively to the "hot" and "neutral" conduc(cid:173)
`tor leads of the a.c. supply conductor cord 18 (FIG. 2).
`The electrical screw terminals 48A,48B are posi(cid:173)
`tioned low on the circuit housing 38 and, as mentioned,
`are recessed to facilitate hook-up. Both terminals are 25
`displaced ninety-degrees with respect to the touch input
`spring contact 56 to provide maximum clearance dis(cid:173)
`tances in the event the leads of the conductor cord 18
`stray during hook-up.
`Still further, the touch control light socket 12 in- 30
`eludes conductive contact means, preferably in the
`form of a resilient electrical leaf spring contact 56,
`which is supported by the circuit housing 38 and electri(cid:173)
`cally connected to the sensing circuit 44 thereon. The
`spring contact 56 is then attached to and extends 35
`through the circuit housing 38, and at its outer end
`portion 58 extends along and projects outwardly from
`the side 60 of the circuit housing 38. As shown in FIG.
`2, the spring contact 56 is thus disposed for placement
`between the exterior side 60 of the circuit housing 38 40
`and the interior side of the light socket shell 22, and can
`be aligned with the opening 36 in the cardboard liner 34,
`so as to extend therethrough, when the touch control
`socket 12 is installed within the light socket shell 22.
`The spring contact 56 makes electrical contact with the 45
`shell base 26 which is fabricated from an electrically
`conductive material. The shell base 26 is, in turn, con(cid:173)
`nected to other electrically conductive exterior por(cid:173)
`tions of the lamp 10, such as the base 16 via the conduc(cid:173)
`tive central pipe 24. When the circuit housing 38 and 50
`insertion socket 40 are installed within the light socket
`shell 22, the spring contact 56 is thereby completely
`hidden, being inaccessible from the exterior of the lamp
`10. By virtue of the spring contact 56, the need for an
`exterior wire or clip is eliminated. The spring contact 55
`56, coupled to the shell base 26, is adapted to convey to
`the circuit 44 an electrical touch sensing signal gener(cid:173)
`ated when a person touches an electrically conductive
`exterior portion of the lamp 10 which is electrically
`connected to the light socket shell base 26.
`It should be understood that the spring contact 56 can
`take the form of the leaf spring, shown in FIG. 3, or of
`any spring-like mechanism, such as a spring wire or a
`conductive plastic pad or finger.
`Contact from the socket shell 22 to the exterior of the 65
`lamp 10 can be accomplished in various ways. The
`attachment of the socket shell 22 to the lamp body 14 is
`sufficient for metal lamps. For wood lamps, the center
`
`60
`
`4,764,708
`
`6
`pipe 24 may be used to convey the signal from the
`lamp's metallized base to the socket shell. Many other
`styles of lamps also use this pipe concept to hold the
`various lamp parts together. For ceramic lamps, the
`entire lamp body can be made conductive through con(cid:173)
`ductive chemical coatings.
`Referring now to FIG. 5, the touch sensing electrical
`circuit 44 basically includes an a. c. switching device 62,
`such as a triac, electrically connected in series with a
`light bulb 64 of the lamp 10 when the latter is inserted
`into the insertion socket 40 of the touch control socket
`12. The a.c. switching device 62 has bi-directional con(cid:173)
`ducting and nonconducting states wherein the light
`bulb 64 is respectively turned "on" and "ofr• during the
`a;c. voltage half-cycle as required to control lamp inten(cid:173)
`sity. Using low-power LSI circuitry and pulsed triac
`gating, the primary heat generating source within the
`circuit 44 is the triac 62. Heat is conducted away from
`the triac 62 by way of one of the screw terminals 48.
`The triac's heatsink tab, which is electrically isolated
`from the triac, fastens directly to the terminal 48 for
`maximum heat transference. Although either the "hot"
`48A or "neutral" 48B terminals could be used for heat
`conveyance, the "hot" terminal48A is preferred since it
`is already common to the triac's input. In this manner,
`breakdown in insulation between the triac's junction
`and the triac's mounting tab merely causes the light bulb
`64 to remain on indefinitely. This mode of failure is,
`however, preferable to an across-the-line short that
`would occur if the triac 62 were mounted to the neutral
`terminal 48B. The heatsink terminal reduces the triac's
`heat rise without bringing heat into the circuit 44, thus
`adding to the reliability of the entire unit.
`In addition, the circuit 44 includes an operating mode
`control subcircuit (U1) 66, being preferably in the form
`of a standard LSI circuit designated LS7237 and com(cid:173)
`mercially available from LSI Computers Systems, Inc.
`The mode control subcircuit 66 is electrically con(cid:173)
`nected at Pin 8 to the triac 62 through a diode D4.
`Operation of the mode control subcircuit 66 will be
`described in greater detail later.
`Further, a capacitance detection and compensation
`subcircuit 68 is electrically connected to the spring
`contact 56 for detecting a touch-responsive signal gen(cid:173)
`erated by a person touching a conductive portion of the
`lamp 10.
`Capacitive sensing is accomplished by monitoring the
`amount of current flowing. through the touch sensor
`input to earth ground. Voltage necessary to detect this
`capacitance is provided by operation of the circuit 44
`from the "hot" side of the a.c. supply conductor. For
`this reason, line polarity (i.e. hot and neutral hook-up) is
`important for proper sensing. If the polarized plug 20 is
`used however, correct polarity is automatically as(cid:173)
`sumed. U.L. already requires that all lamps use such a
`plug to protect the user from shock during relamping.
`The subcircuit 68 monitors changes in lamp capacitance
`conveyed thereto via the spring contact 56. Wore par(cid:173)
`ticularly, resistors R1,R2 of the subcircuit 68 develop a
`signal across resistor R3, whose amplitude is propor(cid:173)
`tional to the amount of capacitance between the touch
`sensor input and earth ground. Resistors R1,R2 limit the
`sensing current to less than 40 microamps, which is
`unperceivable by most users. The redundant resistor
`design serves to protect the user from shock in the event
`one of the resistors becomes shorted for whatever rea(cid:173)
`son. Resistor R3 is chosen to limit the amount of signal
`
`

`

`4,764,708
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`40
`
`7
`to a reasonable level when operating with large(cid:173)
`capacity lamps.
`Resistive current-limiting at the touch sensor input
`provides several advantages over capacitively coupled
`schemes. Whereas capacitors consist of parallel plates 5
`separated by extremely thin insulators, resistors use a
`resistive film path spread out over a large distance.
`Resistor construction is therefore inherently safer in
`current-limiting applications, and provides better pro(cid:173)
`tection against static-electric discharge, adding to the 10
`overall safety and reliability of the circuit. Such static(cid:173)
`discharges can occur when the user walks across a
`carpet and touches the lamp. Effective current-limiting
`also reduces the amount of "shock" felt during such
`static discharges.
`Resistive limiting also reduces problems with contact
`resistance between the touch input spring 56 and the
`socket shell base 26, and the other interconnecting
`metal parts of the lamp 10. In the circuit presented
`herein, sensor input resistance has a negligible effect 20
`since it is only a small percentage of the total input
`resistance. Some capacitively-based touch designs can(cid:173)
`not tolerate even 10 K of input resistance, making them
`unreliable for spring contact designs.
`Lastly, resistors offer a constant impedance over 25
`frequency. The circuit uses this resistance in a low-pass
`filter to attenuate most common RF noise sources.
`Capacitively-based input designs offer no such filtra(cid:173)
`tion, and consequently suffer from noise pick-up from
`radio transmitters, local television oscillators, wireless 30
`intercoms, etc., causing false triggering.
`Still further, the detection and compensation subcir(cid:173)
`cuit 68 is composed of two different time-constant cir(cid:173)
`cuit portions, a touch-sensitive capacitance circuit por(cid:173)
`tion 70 and an ambient-sensitive capacitance circuit 35
`portion 12, which produce opposing-polarity_ signals
`which vary in response to changes in lamp capacitance.
`Specifically, Cl,Dl and C2,D2, in conjunction with
`input resistors Rl,R2, form the touch and ambient de-
`lays, respectively, of the circuit portions 70,72.
`Also, the circuit 44 includes a level detector means 74
`connected to the operating mode control subcircuit 66
`and to the capacitance detection and compensation
`subcircuit 68 for receiving the opposing-polarity signals
`therefrom and resistively summing the same for produc- 45
`ing a compensated detection signal wherein the effects
`of varying ambient conditions have been substantially
`eliminated. Specifically, the opposing-polarity outputs
`from both circuit portions 70,72 are summed together
`by resistors R4,R5 and applied to the base of transistor 50
`Ql. If it is assumed that the lamp capacitance signal on
`the circuit input is steady, and that the summing resis(cid:173)
`tors R4,R5 are equal and neglecting resistor R6, the sum
`of the opposing voltages developed across Cl and C2 is
`zero and Ql's collector remains OFF, outputting a log- 55
`ic-0 (V dd) to Ul Pin 5. This zero voltage represents
`nondetection of a touch responsive signal.
`If, however, the circuit input sees a sudden increase in
`lamp capacitance, caused by a person touching the lamp
`10, the voltage across R3 increases, causing both C1 and 60
`C2 to begin charging to a higher level. Because the time
`delay of touch circuit portion 70 is much shorter than
`the time delay of ambient circuit portion n, the voltage
`across Cl charges more quickly, causing the voltage at
`the base of transistor Ql to fall. If the voltage drops to 65
`a given level (in this case the Vbe level of Darlington
`Ql) then transistor Ql conducts, dumping the charge on
`filter capacitor C4 and outputting a logic-1 (Vss) signal
`
`8
`to Pin 5 of the mode control circuit (Ul) 66, indicating
`that a touch-responsive input signal has been detected.
`This output persists until the voltage on ambient delay
`capacitor C2 can rise sufficiently to cancel the touch
`delay signal voltage imbalance. Resistor R6 provides a
`small imbalance in the summing impedances to bias
`transistor Ql closer to its tum-on voltage, increasing the
`sensitivity of the circuit 44. Component C3 is a high-fre(cid:173)
`quency bypass capacitor to attenuate RF noise at the
`circuit input.
`Therefore, the circuit 44 senses touch by detecting
`increases in lamp capacitance seen on the input the
`moment the user touches the lamp. The amount of ca(cid:173)
`pacitance increase will vary, depending on the person's
`15 body capacitance which is related to body size and
`position relative to the earth ground, and the amount of
`capacitance and resistive coupling provided by the
`touch. In general, however, the amount of increase is
`usually significant even for large-capacity lamps.
`A simple fixed-threshold capacitance detection
`scheme, such as that recommended by the manufacturer
`of Ul, would not really be practical for touch lamps
`since the lamps themselves will vary in capacitance,
`causing random tum-on. Variables for capacitance in(cid:173)
`clude the size of the lamp, its composition, placement,
`and room humidity. For this reason the circuit 44 has an
`automatic-sensing compensation subcircuit 68, as just
`described, which eliminates effects of slowly varying
`ambient conditions on the touch control circuit's sensi(cid:173)
`tivity.
`The dimming control logic of the circuit 44 is built
`around the operating mode control circuit (U1) 66, a
`standard LSI chip identified earlier, which is specifi(cid:173)
`cally designed for touch control dimmers. The dimming
`logic advances the dim level to the next step each time
`the voltage on Ul's Pin 5 rises with each detected
`touch. The circuit 66 uses a standard single-filament
`light bulb 64 and varies the lamp brightness by phase(cid:173)
`controlling the power to the lamp's filament. The cir(cid:173)
`cuit 66 delays the tum "on" of the triac 62 so many
`milliseconds every half-cycle of the a.c.line, thus reduc(cid:173)
`ing the voltage to the lamp to produce the desired dim