This invention relates to apparatus adapted for controlling the flow of current through a load in an electrical circuit.

The conventional arrangement for controlling flow of current, for example from the domestic alternating mains supply, through a load, for example a lamp, is to provide a lamp with the switch operated by hand.

Other forms of control has been suggested and are in use for particular forms of apparatus. Thus, for example, touch control has been employed previously, for example, in lift (elevator) panels and the like. Such controls have heretofore necessarily employed a touch plate, switching being triggered by a user touching the plate to connect it to earth.

In contrast to such prior touch plate controls, the present applicants have devised a highly novel and original arrangement which completely avoids the need for any touch plate as such.

The present invention provides electrical control apparatus comprising: control means adapted for connection in an electrical circuit to control current flow through a load coupled in said circuit, the control means being adapted for operation in said circuit by a change of potential at a control point of said control means; and a third party body comprising a plant bedded in damp soil, said third party body being insulated from earth, and being electrically coupled to said control point, whereby, in operation, touching said plant gives rise to a change in potential at said control point.

In the preferred arrangement, the load is a lamp such as a table lamp operated by the alternating mains supply. The lamp may comprise a support which stands upright in a plant pot or other container. The stem houses the electrical components of the control means and of the

light fitting for the lamp and supports a lampshade or the like. The apparatus as a whole provides and attractive display with aesthetic appeal. In addition, the lamp has no apparent switch spoiling its external lines as in conventional lamps. Indeed, until a user realises that touching the plant will cause the lamp to be lit or switched off, there is no mechanism apparent by which to operate the lamp at all.

In the most preferred arrangement wherein part of the lamp stem is embedded in the soil, one plate of a capacitor is provided by a conducting plate comprising a foil in contact with an inner surface of the lamp stem housing, the other plate of the said capacitor being effectively provided by the soil in contact with the corresponding outer surface of the lamp stem housing, the dielectric material for this effective capacitor being ^" formed by the insulating material of the lamp stem housing proper. With this arrangement, which is particularly suitable for domestic lamps, there is no direct current link between the control means circuit elements coupled to the alternating mains supply and the plant so that there is effectively no danger of a substantial discharge current leaking through a user of the lamp.

The lamp control means circuit suitably incorporates a conventional dimmer arrangement which can also be operated from the same touch control provided by the plant, as will be explained in further detail below.

The invention is hereinafter described more precisely by way of example only with reference to the accompanying drawings, in which:

Fig 1 shows a highly schematic diagrammatic view of an embodiment of apparatus constructed in accordance with the present invention;

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Fig 2 shows in partial sectional view a lamp stem of a preferred embodiment of our apparatus, the stem being adapted to stand upright in a plant pot or other container alongside the plant or, preferably, amongst a group of plants, and the control means being provided within the said stem; and

Fig 3 shows a circuit diagram for a preferred embodiment of the lamp of Fig 2.

Referring first to the schematic view of Fig 1, a load 1 and a control means 2 are connected in series in an electrical circuit 3 which is coupled to the alternating mains supply 4. A plant 5 bedded in damp soil 6 in a plant pot 7 or other suitable container is insulated from earth by an insulating block 8. In practice the plant pot or other container 7 may itself be made of electrically insulating material requiring no specific additional block such as 8. The plant 5 is electrically coupled to the control means 2. The arrangement is such that electric power to the load 1 can be switched by touching the plant 5 as schematically illustrated so as to give rise to a change in potential at a control point in the control means 2 effective to connect or to disconnect the alternating supply 4 through the control means 2 to the load 1.

Electrical coupling between the plant 5 and the control means 2 is indicated in Fig 1 in an entirely general and schematic fashion. In practice the plant 5 standing in damp soil 6 is suitably physically spaced from electrical components wired to or forming part of the control means 2. For example, the control means 2 may include a plate or foil or the like directly connected to the control point of the control means circuitry, the plate or foil either standing in the damp soil 6 or being provided interiorly of a support formed

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of insulating material so that the foil or the plate serves as one plate of a capacitor for which the other plate is effectively damp soil about the exterior surface of the support, the support being formed of a dielectric insulating material. In these various arrangements moisture in the soil provides the electrical connection to the plant. The load 1 is preferably, though not necessarily exclusively a lamp.

Fig 2 shows the preferred arrangement for a lamp. The lamp comprises a lamp stem, the main body of which is formed by insulating housing 10, surmounted lamp holder 11. Securing nut 12, through which mains cable 13 passes, forms a water-tight seal with the base of housing 10. The lower portion of housing 10 defines a lower cavity 14, in which a conducting foil 15 makes contact with part of the inner surface of housing 10. Foil 15 is coupled by means of a wire 16 which passes together with mains cable 13 through a seal plug 17 into an upper cavity 18 defined by housing 10 and a cap 19. Cavity 18 contains the electric circuitry for the control means 2, provided here in the form of a circuit board 20 to which a sensitivity switch unit 21 is connected, the conductor wire 16 from foil 15 being connected to the sensitivity switch unit. The circuit board 20 also mounts the other electrical components of the control means, which components are embedded in resin 22. Neutral wire 23 of mains cable 13 passes through cavity 18 and cap 19 and forms one of two terminals for an electric lamp, such as, a light bulb, which may be mounted within lamp holder 11. From the other of the two terminals, the neutral line passes through cap 19 and is connected to the electrical components mounted on circuit board 20.

Live wire 24 of mains cable 13 is connected directly to the electronic components mounted on circuit board 20.

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In operation, lamp stem 9, with securing nut 12 in place forms a sealed unit. The basal portion of stem 9 is bedded in damp soil contained in a suitable container, such as container 7, the damp soil also being host to the roots of a living plant or several living plants such as plant 5. The outer surface of stem housing 9 is in contact with water in the soil. The water present in the soil, together with water present throughout the vascular system of the plant, by virtue of anionic and cationic species naturally dissolved therein, providing a continuous electrolytic medium between the outer surface of stem housing 9 and any part of the plant.

In the preferred arrangement illustrated, the water in contact with the basal portion of the outer surface of housing 9 forms one plate of a capacitor, the other plate of which is formed by the metallic foil 15 in contact with the inner surface of the basal portion of housing 9. The insulating material of housing 9 acts as its dielectric material. Foil 15 is connected via a direct resistive pathway (the electrical resistance of which depends on the setting of a sensitivity switch 25 which protrudes through housing 9 and is adapted to be operated manually to control the setting of the sensitivity switch unit 21) to a control point of the circuitry of control means 2 as is explained in more detail below with reference to Fig 3.

Fig 3 schematically illustrates the electrical circuitry. The load 1 is shown connected to the neutral terminal N of the alternating mains supply 4. The control means 2 is coupled between the load 1 and live terminal L of the alternating supply. Control means 2 features a triac TR controlled by an integrated circuit IC which provides the clock circuitry for the triac TR. Switching of the circuit 2 is effected by change of

potential at a control point therein, namely at pin 5 of integrated circuit IC, as will be explained. A smoothing circuit comprising a shunt capacitor Cl and a series choke LI smooths the voltage across the triac TR.

A direct voltage setting circuit 26 is coupled in parallel with the triac and its voltage smoothing circuit to the mains supply and is adapted to establish a constant potential difference between pins 1 and 7 of integrated circuit IC. Direct voltage setting circuit 26 comprises resistor Rl, capacitor C2 and Zener diode Z connected in series across the mains supply. A diode Dl is coupled between the junction between capacitor C2 and zener diode Z and pin 7 of integrated circuit IC Capacitor C3 which is connected across pins 1 and 7 of integrated circuit IC serves to smooth the resultant D.C. voltage.

The circuit of Fig. 3. is electrically coupled to the damp soil 6 in which the plant 5 is located, in this case via foil 15 mounted interiorly of housing 9 of the lamp stem and serving as one plate of a capacitor. Foil 15 is directly connected via sensitivity circuitry 27 associated with sensitivity switch unit 21 to the control point pin 5 of integrated circuit IC. A diode D3 is connected between pins 7 and 5 of the integrated circuit IC and a further diode D4 is connected between pin 5 and pins 1 and 2 of the integrated circuit. This arrangement of the diodes D3 and D4 allows the potential difference to be maintained between pins 7 and 1 of integrated circuit IC, provided that pin 1 is at a more positive potential than pin 7. Diodes D3 and D4 also facilitate rapid re-establishment of the resting potential at pin 5 after a change of potential caused by touching the plant. Resistor R9 defines the resting potential of pin 5 with respect to the potential at pin 1. With this arrangement,

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a change of potential at pin 5 produces a signal at pin 8 of integrated circuit IC which triggers gate G of the triac TR via intervening diode D2. Timing of the firing signal from pin 8 is controlled by the clock mechanism of integrated circuit IC which operates by charging and discharging of capacitor C4 which is coupled between terminal Al of the triac TR and pin 3 of integrated circuit IC. Resistor R2 and capacitor C5 are connected in series between terminal A2 and terminal Al of the triac TR and the junction between resistor R2 and capacitor C5 is connected to pin 4 of the integrated circuit. The combination of resistor R2 and capacitor C5 serves to filter out unwanted fluctuations in potential generated by the clock circuitry of the integrated circuit. The remaining pin 6 of the integrated circuit is directly connected to pin 7.

Sensitivity circuitry 27 comprises a resistive pathway comprising resistors R3, R4, R5, R6, R7 and R8 connected in series between pin 5 of integrated circuit IC and the foil 15 and is effective to set the change of potential at pin 5 required to be caused by touching the plant which is effective to trigger integrated circuit to generate a signal at pin 8 to trigger the triac TR. Sensitivity switch 25 is switchable between standard "S", medium "M" and high "H" positions. As will be seen from Fig. 3, moving the switch to position "M" shorts out resistors R7 and R8 and moving the switch to position "H" additionally shorts out resistors R5 and R6.

The circuitry 2 illustrated is effective to act not only as a simple switch but also as a dimmer circuit with a fixed clock cycle provided in effect by integrated circuit IC which in the preferred embodiment comprises a 576 integrated circuit available from TRIDENT MICROSYSTEMS. Integrated circuit IC is powered by the

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constant potential difference across pins 1 and 7, initially in phase with the mains alternating current source 4 when activated by a change in potential at control point pin 5. An initial triggering change in potential at control point pin 5 causes pin 8 to emit a current pulse at the beginning of each half-cycle of the alternating current source. Each such pulse is transmitted to gate G of triac TR, which thus commences to conduct current at the beginning of each half-cycle, and continues to do so until the potential across the triac drops below a specific holding voltage, as will occur towards the end of each half-cycle. In preferred embodiments, the triac used has a low holding voltage so that conduction ceases essentially as the potential difference across the triac TR drops to zero at end or each half-cycle. Thus, when initially activated in response to a momentary change in potential at control point 5, firing of the triac is in phase with the alternating mains supply. However, if the change in potential is maintained, as by continuing to grasp the plant 5 _r the phase angle at which the triac triggers is progressively changed to cause a dimming function in conventional manner.

In one preferred embodiment the values of the indicated electrical components were as follows:

Rl: . 1.1 KΩ

R2: : 1.5 MΩ

R3: : 1.5 MΩ

R4- : 1.5 MΩ

R5 : 10 MΩ

R6 : 10 MΩ

R7 : 10 MΩ

R8 : 10 MΩ

R9 : 1 MΩ

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Cl: O.lμF

C2: 0.2μF

C3: 22μF

C4: 47nF

C5: 47pF

D1-D4 are each IN4148 diodes available from ITT. Zener diode Z is a nominal 15 volts. The preferred triac TR is designated TYAL 228BS, and is available from THOMPSON.

The foil 15 comprises aluminium foil suitably with an area of 10 sq. inches (64.5 sq. cm). Stem housing 10 is formed of P.V.C. 32mm Conduit plastics material with a thickness of 3mm.

We find that with the circuit component values specified, the change in resistance naturally occurring in the soil 6 and the plant 5 in different atmospheric or room conditions or with different plants, provided that the soil has some moisture (the system will not work if the soil is bone dry) , is not critical and can be accommodated as between the different settings of sensitivity switch 25.

Although we have described the most preferred embodiment hereinabove, it will be appreciated that in a number of significant details, the illustrated arrangement can be varied within the general teaching of the invention. Thus, although the illustrated arrangement incorporates a conventional dimmer circuit as an integral part thereof, it would be entirely possible to construct the circuit omitting the dimmer feature. For example, the circuit could be constructed so as to employ a bistable device directly operated by a change in potential at a control point, successive such changes in potential leading to alternate switching between the two stable states. A simple conventional flip-flop

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circuit incorporating, for example, two transistors would achieve this effect.

Another alternative embodiment incorporates a simple switching circuit comprising, say, a transistor amplifier, which causes current to flow through the load only while the potential of the control point remains unchanged. In other words, to operate this embodiment, the plant must be continuously grasped.

In another alternative arrangement, a latching circuit is used, whereby a change in potential at the control point leads to an irreversible change in the current flowing through the load. A separate switch elsewhere in the circuit is required either to re-connect the circuit if the latching circuit effectively switches the load off (as would be useful in an "off" control for a bedroom lamp operated from a plant standing on a bedside table) , or to switch the circuit off, having first switched it on by using the latching circuit.

While we prefer the illustrated sensitivity circuit whereby manual switching control of the sensitivity control effectively alters the relative potential of control point and plant, and thus the sensitivity of the control point to changing potential of the plant when touched, other methods of sensitivity control can be employed, as for example connecting pin 5 of integrated circuit IC to the suitably adjusted centre point of a potential divider.

Although the invention has been particularly described with reference to the preferred arrangement of Figs. 2 and 3 in connection with the control of an electric lamp, as will be clear from Fig. 1, the teachings of this invention are of general applicability to the control of electric current flow through any electrical load 1.

The incorporation of the dimmer feature makes the lamp embodiment that much more attractive to purchasers.

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The invention may be embodied as a kit comprising a plant container and a lamp stem adapted to be mounted in upright means provided or associated with the container, allowing the purchaser to add soil and whatever arrangement of plants he desires about the lamp stem.

In another alternative practical embodiment, a form of apparatus in accordance with this invention may be sold to purchasers in the form merely of a lamp stem and means adapted for standing the lamp stem upright in whatever plant pot or other insulated container the purchaser of the kit desires, soil and plants being added subsequently. Because the preferred arrangement described in detail employs a purely capacatitive link between the circuit elements and the damp soil, practical embodiments of our apparatus can be produced which are fully in accordance with applicable British standard since they avoid altogether any direct current leakage between the circuitry and a human operator touching a plant.

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