SPECIFICATIONImprovements in or relating to automatic light switchesThe present invention relates to automatic light switches. Such a switch may be used to control illumination of one of more light in a room.
According to the invention, there is provided an automatic light switch comprising a switching element, means for detecting the pressure in or entry into an enclosed space of a person, and a timer arranged to actuate the switching element for a predetermined period in response to detection of pressure or entry by the detecting means.
Preferably, a light sensitive element is arranged to inhibit actuation of the switching element in response to a light level exceeding a predetermined level.
The invention will be further described, by way of example, with reference to the accompanying drawing, which is a block diagram of an automatic light switch constituting a preferred embodiment of the invention.
The automatic lights which shown in the accompanying drawing has a three pole mains input with the first connection E thereof connected to a common line 1 and the live and neutral inputs Land N connected to a two pole ON/OFF switch 2. The neutral line from the output side of the switch 2 is connected to one input terminal of a power supply 3 and to the neutral terminal N of a load output connector. The live connection from the switch 2 is connected via a fuse 4 to the other input of the power supply and to a triac switch 5 and a zero crossing detector 6. The output of the switch 5 is connected to a live terminal L of the load output. The output of the power supply 3 comprises a low voltage D.C. supply for the electronics of the light switch with a red light emitting diode 7 connected thereacross to indicate that the light switch is receiving mains power.A further output of the power supply 3 supplies timer sync pulses, at mains frequency or at a multiple thereof, to an electronic timer 8.
The timer 8 comprises a digital synchronous programmable counter which counts the sync pulses from the power supply 3. A nine-way switch 9 is connected to the counter to selec select theON-duration of the timer, for instance in half minute intervals so that the ON-duration may be set from 0.5 to 4.5 minutes or in 1 minute intervals from 1 to 9 minutes. A green light emitting diode 10 is provided for indicating the ON-duration of the timer. This light emitting diode 10 may be arranged to flash approximately 15 seconds before the end of the ON-duration for the purpose of simplifying timing setting procedure.
The timer 8 has an input and output connected to an output and input, respectively of control logic 11.
Another input of the control logic 11 is connected via an amplifier 12 to the output of a presence or entry detector 13. The detector 13 is sensitive to the presence of a person in an enclosed space, or to the entry of a person into an enclosed space. For instance, when the automatic light switch is used to control a light in a domestic environment such as a living room, the detector 13 may comprise a doppler microwave or infrared detector sensitive to movement of the person in the room. Alternatively, the detector 13 may be of the interrupted beam type, for instance a light source and light sensitive element, arranged across a doorway or other entrance to the room.
The control logic 11 is further connected to an integrator 14 whose input is connected to the output of an amplifier 15. The input of the amplifier 15 is connected via a level setting control 16 to the output of a photocell 17 having a light-sensitive characteristic similar to that of the human eye. A yellow light emitting diode 18 is connected to the control logic 11 for indicating when a light level in excess of a predetermined level is received by the photocell 17.
The control logic 11 has a further input connected to set and reset controls 19 and 20, respectively, for over-riding control functions so as to test the operation of the triac switch 5 and the light connected thereto. The control logic 11 has a control output connected to the zero crossing detector 6, which in turn is connected to the control element of the triac switch 5 to permit switching on when the main supply voltage passes through zero so as to reduce load surge and radio frequency interference.
In operation, the automatic light switch is arranged to control one or more lights in an enclosed space, for instance a domestic living room.
The lights to be controlled are connected between the live and neutral terminals Land N of the load output, so that the triac switch 5 controls the live connection to the light or lights. The presence of a person in or the entry by a person into a room is detected by the detector 13, which supplies a signal to the control logic 11. Upon receipt of this signal, the control logic 11 actuates the timer 8, which supplies a signal to the control logic 11 for a duration selected by the control 9. The control logic 11 supplies a signal for the timer duration to the zero crossing detector 6 which, in response thereto, triggers the triac switch 5 so as to supply to the light or lights. The light or lights are then switched off at the end of the timer duration unless the timer is re-actuated by a signal from the detector 13.
Thus, the light or lights are switched on automatically whenever anyone is in the room or enters the room, and are switched off automatically either by the timer 11 or when the detector 13 supplies a signal indicating the absence of anyone in the room.
In the case where the detector 13 is a doppler-type of detector, the lights remain switched on for as long as movement is detected in the room. In the case of an interrupted beam type of detector, the lights are awitched on in response to interruption of the beam for a predetermined time and remain on provided the beam is interrupted prior to the end of the timer on-duration.
When the photocell 17 supplies a signal corresponding to a light level greater than a predetermined level, output signals from the control logic 11 for switching on the lights are suppressed so that the lights remain extinguished. Thus, the lights are prevented from being illuminated when ambient lighting levels are sufficiently high, for instance during daylight. The photocell 17 may be positioned such that it is insensitive to the illumination provided by the lights. Alternatively, the photocell and associated circuitry may be disabled once the lights have been illuminated by means of the control logic 11.
The detector 13 may be any suitable type of detector for indicating the presence of a person in the room or the entry of a person into the room. For instance, any type of intruder detector may be utilized. In the case of a detector utilizing electromagnetic radiation, although mention has been made of such a detector based on doppler principles, the detector may have any other form capable of sensing a disturbance in an electromagnetic field caused by the presence of a person in the room.
Also, the detector may be based on other principles, such as ultrasonics. In this case, the detector may be of the type based on doppler principles or of any other type sensitive to disturbance of ultrasonic signals caused by the presence of a person in the room. In the case of a beam interruption detector, the detector may comprise a source of electromagnetic signals, such as light or infrared, or a source of ultrasonic signals or other acoustic signals, with a corresponding transducer. Further, the detector may be sensitive to a change in inductance or capacitance caused by the presence of a person in the room.
Further, although the automatic switch has been described with reference to the control of lights, it may be used for other control purposes, for instance to control a source of heat in the room.