WO1993010550A1

WO1993010550A1 - Light operated switch

Info

Publication number: WO1993010550A1
Application number: PCT/GB1992/002150
Authority: WO
Inventors: Laszlo Hamar
Original assignee: Laszlo Hamar
Priority date: 1991-11-20
Filing date: 1992-11-20
Publication date: 1993-05-27
Also published as: AU2949992A; GB9124562D0; GB9410176D0

Abstract

The invention provides a light operated switch which, in a first embodiment, is provided for a vehicle warning light arrangement (10). The switch includes a light sensitive sensor, e.g. a light sensitive diode or resistor (12) which supplies an electrical signal proportional to a sensed light value to enable a switch (14) for use in switching the system on or off by connection to a battery (18). Switching means (16) receives the signal from the sensor and supplies it to a comparator (24) where it is compared with a pre-determined value stored therein. If the value is exceeded a second switch (26) is operated to actuate light array (20, 22). A timing unit (28) preferably measures the time period for which the measured light value exceeds the pre-determined value, where the duration of this exceeds a pre-determined period, the pre-determined value stored in the comparator (24) is adjusted to compensate. The light operated switch may also be incorporated in a toy or safety device.

Description

LIGHT OPERATED SWITCH

This invention relates to a light operated switch which can be used to operate a warning light on a motor vehicle so as to be effective only when such warning is required by the approach of another vehicle.

Warning lights intended, for example, to warn or otherwise indicate the presence of a stationary vehicle for other road users are already known. Commonly, these lights are wired into a vehicles primary ignition circuitry and must be left in either an "on" or "off" condition. A problem inherent in this arrangement is that when a vehicle is left unattended for long periods of time, a light left in "on" condition may drain a large proportion of the battery capability, thus leaving insufficient charge to start a vehicles engine.

A further problem is that the warning light can only be left fully on or fully off for all its operable periods. Thus, the warning light is not responsive to a change in visibility conditions which may require its use, after it had been initially placed in an off condition, or alternatively, the warning light will not be switched off where its use is no longer required due to an absence of traffic in the vicinity of the vehicle or an improvement in ambient light conditions.

It would be advantageous to provide a light operated switch to control a vehicle warning light arrangement which is effective to conserve a vehicles battery charge and to be operated only when required to warn other road users of the presence of a stationary vehicle.

With this object in view, the present invention provides a light operated switch including a light sensor connected to a lighting arrangement such that the lighting arrangement will be operated only when the sensor detects a change in ambient light which change exceeds a pre-determined threshold value.

The light sensor may be a light dependent resistor or a photo-transistor. Advantageously, the sensitivity of the resistor has a variable value so that the sensor can be adjusted for range and variants in ambient light conditions.

It will be understood that with such an arrangement, a vehicle provided with a warning light controlled by a light operated switch according to an aspect of the invention, may be left in a parked condition with the arrangement switched on and with minimal power drain. The lighting arrangements will be activated as a warning when the presence of an approaching vehicle is detected by the inpingement of light on the light sensor. Thus, the lighting arrangement proposed is not in use at all times and is directly responsive to the amount of traffic passing the parked vehicle.

An alternative use for such a switch is in a childrens toy where the lighting arrangement is located, e.g. as its eyes. In such a use the lighting arrangement will be activated by a decrease in light such that the toy can be used as a "comforter" or as a road safety device.

In a further aspect of the invention, a vehicle warning light arrangement comprises a light sensor located at the rear of the vehicle and connected by switching means to the vehicles existing lighting arrangement, the switching means being effective to operate the lighting arrangement only when the lighting sensor detects a light source directed towards the sensor.

It will be appreciated that in this aspect of the invention, the warning light arrangement makes use of the vehicles existing light array, for example, side lights or brake lights which are thereby caused to be actuated when the sensor is operated.

Preferably a time delay mechanism is provided within the light operated switch means such that operation of the lighting arrangement will be maintained for a pre¬ determined short period of time after the light source is no longer directed towards the light sensor. In this way, if any sudden or temporary obscuration of the light source will not automatically result in switching off of the lighting array.

In a preferred embodiment for use as a vehicle warning light, the vehicles lighting arrangements, both front and rear, are actuated by operation of the switching means such that the vehicle is illuminated in all directions. In this instance, it may be preferable to provide an additional sensor located at the front of the vehicle, particularly where the road with adjacent to the parked vehicle is relatively narrow.

In an alternative aspect of the invention, a combined vehicle warning light arrangement is provided comprising a housing enclosing a light sensor and a lighting arrangement, the arrangement and the sensor being connected by switching means operative to activate the lighting arrangement only when the sensor is acted upon by an external light source.

It will be understood that with such a modified arrangement, the enclosed unit may be mounted in the rear front vehicle as desired and in a manner similar to that for the mounting of known additional brake light units.

Alternatively, the housing can be mounted on the vehicles exterior. However, this would make it vulnerable to external forces, for example, collisions and also to theft or similar actions.

In order to ensure that the sensor is not actuated for long periods by an increase in light impinging thereon, e.g. as a recause by an adjacent parked car left with its main lights on or an adjacent building light left on for an extended period, the arrangement preferably includes a comparator having an initially pre-set light value which will cause the light to be switched on when the value is exceeded. The comparator also preferably includes means to adjust the pre¬ set value, to preferably equal a light value sensed by the sensor, when the original pre-set value is exceeded for a pre-determined time period.

Additionally, the comparator also includes means to re-set the light value to its original pre-set value when the sensed light value falls below the current pre-set value for a pre-determined time period.

A first practical embodiment of the invention provides a light operated switch in four sections, a first section including two photo-transistors used as sensors, connected to a second section including amplifier means and comparator means operative to compare a signal received from the photo- transistors with a pre-determined threshold value and, if this is exceeded, to transmit that signal to a third section including a timer and a threshold modifier operative to increase or decrease the threshold value according to the magnitude of the signal received by the photo-transistors, and a fourth section operative to output a signal to a lighting arrangement to activate same so as to act as a warning indication.

The invention will now be described further by way of example with reference to the accompanying drawings in which:- Fig. 1 is a block diagram of a first preferred embodiment of the invention;

Fig. 2 is a circuit diagram of a practical embodiment of the invention; and

Fig. 3 is a circuit diagram of a second practical embodiment of the invention.

Referring to the accompanying drawings, in Fig. 1, a preferred embodiment of the invention provides a light operated switch adapted for use as a vehicle warning light arrangement 10 including a light sensitive sensor 12, for example, a light sensitive diode, photo-transistor or other similar light sensitive detector, operative to measure the amount of light inpinging on the sensor and produce an electrical signal proportional to that sensed light value. The sensor 12 is connected to an enabled switch 14 which enable the system operator to determine whether this system is in an on or off mode. The sensor 12 is further connected to switching means 16 which is connected to a battery 18 which may be the vehicles own normal battery source or may be a supplementary battery connected solely to this arrangement.

The switching means 16 are also connected to at least one lighting arrangement or array 20, 22. In one embodiment of the invention this lighting arrangement is an additional light intended solely for the purpose of warning other vehicles of the presence of a stationary vehicle. In an alternative embodiment, the light 20 may be the vehicles only existing lights, for example, side lights, rear lights or brake lights etc.

It will be appreciated that with the enables switch 14 operated so as to activate the systeme, the sensor 12 is operative to detect the lights of any vehicle approaching the sensor. When such an approach is detected, the sensor 12 operates the switching means 16 enabling the lighting arrangement 20 to draw power from the battery 18 and hence illuminate the parked vehicle. Although the enable switch 14 for the sensor will be activated for the entirety of the period during which the vehicle is parked, the battery 18 will not be required to power the light of lights 20, 22 for this full time period and hence battery charge will be conserved.

The switching means also includes a comparator 24 which compares the light value measured by the sensor 12 with a pre-determined value stored in the comparator 24. The pre¬ determined value is preferably set by external controller (not shown) such that adjustments can be made for a required range and for variance in ambient light conditions. If the sensors measured value exceeds the pre-determined value, the comparator 24 actuates a second switch 26 which in turn operates the light array 20, 22 to illuminate to parked vehicle.

In order that the pre-set value may be sensitive to a change in ambient light conditions, i.e. an increase due to an ad acent building light being switch on, the comparator preferably also includes a timing unit 28 which will measure the time period for which the measured light value exceeds the pre-set value. Where this time period exceeds a pre-determined period, for example, 30 seconds, the timing unit 28 generates an output to the comparator 24 so as to reset the pre-determined light value stored therein to a new value equal to the current measured value. In this way, a relatively long term increase in light received by the sensor 12 will not cause the arrangement to be permanently

In such an embodiment, the switching means 16 will also include a second comparator 30 which also receives the outpiitted measured light value from the sensor 12. This second comparator 30 is activated when the pre-set value of the first comparator 24 is altered and is operative to compare the measured light value with the original pre¬ determined stored value. When the measured value falls below the original pre-determined value, the second comparator 30 acts to re-set the value stored in the first comparator 24 to its original level. Thus, when the cause of an increase in ambient light is removed, i.e. the light is turned off or the vehicle is moved away, the arrangement is re-set to its original condition.

It is possible to present the vehicle warning light arrangement in two alternative embodiments. Firstly, the entire system, sensor 12, enables switch 14, switching means 16, battery 18 and lights 20 may be provided in a casing or housing (not shown) which is provided with fixing means for attachment to a vehicle. Such a self contained assembly could be mounted inside the rear window of a vehicle or to its rear bumper.

Alternatively, the sensor means could be mounted at a position remote from the lighting arrangement and its associated switching means, for example, the sensor could be provided on or adjacent to the vehicles bumper or inside the rear window of a vehicle and attached to the vehicles normal lighting array. In this instance, it would probably be advantageous for the sensor and the light to draw power from the vehicles own battery and this would of course, simplify connection of the system to the vehicles existing electrical system.

In order that the lights in the vehicles should not be turned off immediately, a light source no longer inpinges on the sensor, a time delay factor may advantageously be included in the switching means so that the light 20 remains illuminated for a short, pre-determined period after the sensor is no longer acted upon by a light. It will be appreciated that by utilisation of either of the two above described embodiments, the vehicle warning light arrangement according to the invention provides a system which is both responsive to traffic conditions and light conditions and is operative to conserve battery charge during periods when illumination of the vehicle is not required.

In a first preferred practical embodiment of the invention, a circuit 40 for a warning light includes a power input 41 connected to an amplifier circuit referred to generally by reference numeral 46. The amplifier circuit 46 includes first and second resistors 48, 50 and a first transistor 52 connected to two photo-transistors 42, 44. This arrangement ensures that any light differential sent by the photo- transistors 42, 44, causes an output to be generated at one pin of the first transistor 52. A first compasistor 54 allows this output signal to pass only if it has a varying amplitude, i.e. is respectively an increase or decrease of the value with respect to an ambient light value.

A second amplifier/comparator circuit 50 then passes a signal to a second transistor 58. This responds to such signals by providing an output only if the signal is of sufficient magnitude with respect to two resistors 60, 62. The longitude of the signal modification is determined by the third resistor 64 and a further capacitor 66 is also provided to maintain signal stability.

The output from the second transistor 58 passes through a second diode 68 to a fourth capacitor 70. In turn, this output is passed through a third transistor 72 so as to bias one pin thereof to positive. The threshold of this transistor 72 is determined by the values of two respective resistors 74, 76 connected thereto. When this threshold is exceeded, the transistors output pin is forced low which status permits until the fourth capacitor 70 has discharged to a low charge level which time is determined by the relative values of resistors 74, 76. When the voltage across the fourth capacitor has fallen below this threshold, the output pin of the transistor 72 is forced high and held there by a sixth resistor 78.

Finally, the signal is passed to an output transistor 80 which is held in an off condition by the sixth resistor 78 until the output pin of the third transistor 72 is forced low. At this time, the output transistor is switched on and its subsequent load (light array 82) energised for a duration determined by the discharge time of the fourth capacitor 70.

One important feature of this arrangement is that the system can respond to fast changes in light levels as monitored by the two photo-transistors. These changes can be a relative increase or decrease with respect ambient light, provided that the change has sufficient absolute magnitude and time dependent rate of change.

Thus, unlike known prior art systems, the invention can react to a further change in light level even when the output transistor 80 is energising the load 82. Further by providing photo-transistors which are sensitive to infra-red light, the system can react even in fog or other conditions of normally low or restrictive visability. A second practical embodiment of the invention is shown in Fig. 3. Similar parts are referred to by identical reference numerals and the modified circuit 90 for a warning light includes a power input 41 connected to an amplifier circuit referred to generally by the number 46. The amplified 46 includes first and second resistors 48, 50 and a first transistor 52 connected to a light dependent resistor 42. The first resistor 48 also has a capacitor 44 connected between resistor 48 and a negative rail. This capacitor 44 slows the rate at which the light dependent resistor 42 rises and falls in resistance (controls the sensitivity). This arrangement therefore ensures that any light differential sensed by the light dependent resistor 42 causes an output to be generated at one pin of the first transistor 52. A capacitor 54 allows its output signal to pass only if it has a varying amplitude, i.e. it is respectively an increase or decrease with respect to ambient light.

A second transistor 58 receives a signal passed on by the capacitor 54. Transistor 58 is wired as a comparator circuit with two resistors 60. 62 both of which are connected to the negative rail. When the received signal is of a sufficient magnitude to show a change in the signal already being recieved, the output from the second transistor 58 passes through a second diode 68 to a third capacitor 70. Operation and wiring of this further arrangement as are previously described for Fig. 2.

The advantage of this modified circuit is that it can be activated in normal daylight without the need for a separate switch to turn it on. This is due to the fact that the circuit becomes more sensitive in day time light conditions.

It will be understood that whilst the light operated switch was primarily designed to operate as part of a vehicle warning light arrangement, other uses are also possible. In particular, the switch may be applied to a childrens safety device in the form of a badge or patch which will react to light received, e.g. from a car's headlights at night. In this way, children will be made easily visible by oncoming traffic in otherwise poor visibility conditions. For such a use, the safety device will incorporate its own lighting arrangement and power source, e.g. battery. Similar use as an advertising device is also possible.

A further use for such a light operated switch is in connection with a childrens toy or comforter. In such an embodiment the light operated switch will normally be connected so as to operate a lighting arrangement when the switch detects an absence of lights. In this way the toy will be illuminated in a darkened room or when placed under bed covers etc. Ths lighting arragement preferably comprises or includes such a toys eyes where it represents an animal, e.g. a bear.

The invention is not confined to the foregoing details and variations may be made thereto within the scope of the inventions. For example, the sensor 12 may be any convenient detector operative to sense the presence of an approaching vehicle, thus an ultrasonic or radar type sensor system may be used as an alterative light dependent sensor. In addition to its use on motor vehicles, the invention can also be used on caravans or trailer or on stationary road signs where periodic illumination is desirable. Other variations are also possible.

Claims

1. A light operated switch including a light sensor connected to a lighting arrangement such that the lighting arrangement will be operated only when the sensor detects a change in ambient light which change exceeds a pre-determined threshold value.

2. A switch as claimed in claim 1 in which the light sensor is a light dependent resistor.

3. A switch as claimed in claim 2 in which the sensitivity of the resistor has a variable value so that the sensor can be adjusted for range and variants in ambient light conditions.

4. A switch as claimed in claims 1, 2 or 3 in which a time delay mechanism is provided within the light operated switch means such that operation of the lighting arrangement will be maintained for a pre¬ determined period of time after the detected light source is no longer directed towards the light sensor.

5. A switch as claimed in any preceeding claim in which further includes a comparator having an initially pre-set light threshold value which will cause the light to be switched on when the value is exceeded.

6. A switch as claimed in claim 5 in which the comparator includes means to adjust the pre-set value to equal a light value sensed by the sensor, when the original pre-set value is exceeded for a pre¬ determined time period monitored by timing means.

7. A switch as claimed in claim 6 in which the comparator also includes means to re-set the light value to its original pre-set value when the sensed light value falls below the current pre-set value for a pre-determined time period.

8. A switch as claimed in claim 7 comprising four sections, a first section including two photo- transistors used as sensors, connected to a second section including amplifier means and comparator means operative to compare a signal received from the photo-transistors with a pre-determined threshold value and, if this is exceeded, to transmit that signal to a third section including a timer and a threshold modifier operative to increase or decrease the threshold value according to the magnitude of the signal received by the photo-transistors, and a fourth section operative to output a signal to a lighting arrangment to activate same.

9. A switch as claimed in any preceeding claim for use as a vehicle warning light in which the vehicles lighting arrangements, both front and rear, are actuated by operation of the switching means such that the vehicle is illuminated in all directions.

10. A switch as claimed in claim 9 in which located at the front of the vehicle.

11. A vehicle warning light including a light operated switch according to any of claims 1 to 8 comprising a housing enclosing a light sensor and a lighting arrangement, the arrangement and the sensor being connected by switching means operative to activate the lighting arrangement only when the sensor is acted upon by an external light source.

12. A childrens safety device including a light operated switch according to any of claims 1 to 8.

13. A childrens toy including a light operated switch according to any of claims 1 to 8.

14. A light operated switch substantially as hereinbefore desribed with reference to and as illustrated in the accompanying drawings.