LIGHT SENSITIVE SECURITY SYSTEM

• US 3,811,046 A
• Filed: 01/22/1973
• Issued: 05/14/1974
• Est. Priority Date: 01/22/1973
• Status: Expired due to Term

• Current Assignee: Herbert Levick
• Original Assignee: Herbert Levick
• Inventors: Levick, Herbert
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Nelms, D. C.
• Application Number:
  US05/325,874
• Time in Patent Office: 477 Days
• Field of Search: 250/208,209,206,214,199 307/311 317/124 315/155,156
• US Class Current: 250/206
• CPC Class Codes: G08B 13/1895 using light change detection systems G08B13/194 takes precedence

Abstract

A light sensitive circuit for protection of an area is described. In a first embodiment, a single photocell is mounted together with a control circuit in a housing which fits in a conventional electrical wall box. The photocell is connected in a capacitor discharge circuit to enable a comparison amplifier to recognize whether the photocell is exposed to a normal ambient light change such as from night to daylight or to the beam from a flashlight. A pulse operated latching relay is used to effect a protective response when the photocell is suddenly exposed to a source of light. In an alternate embodiment for a light responsive protection circuit, a pair of photocells are used. One photocell is located to operate to control the enabling of a gate while the other photocell responds to a source of light to effect a desired protective response. A plurality of photocells may be accommodated.

Claims

1. A light sensitive control circuit comprising a source of DC power;

a series network formed of a first resistor and a capacitor, said series network being effectively coupled in series across the DC power source;

a series voltage divider network effectively coupled across the capacitor, said voltage divider network being formed of a first resistor and said light sensitive element;

a discharge circuit coupled to discharge the voltage retained by the capacitor, said discharge circuit including a light sensitive element which registers a change in resistance upon exposure to a source of light, said light sensitive element being coupled to vary the rate of discharge of the voltage charge on the capacitor in response to the rate of light exposure of the element; and

means coupled to the discharge circuit for producing an output signal when said rate of discharge exceeds a predetermined value representative of a predetermined variation of light incident upon the light sensitive element.

2. A light sensitive control circuit comprising means including a capacitor for establishing a voltage charge on the capacitor;

a discharge circuit coupled to discharge the voltage retained by the capacitor, said discharge circuit including a light sensitive element which registers a change in resistance upon exposure to a source of light, said light sensitive element being coupled to vary the rate of discharge of the voltage charge on the capacitor in response to the rate of light exposure of the element;

a comparison amplifier having a pair of inputs with a first input coupled to the discharge circuit;

a voltage reference source coupled to the other input of the comparison amplifier, said voltage reference source having a voltage selected commensurate with a predetermined rate of discharge of the capacitor;

with the comparison amplifier providing an output pulse when the rate of discharge of the capacitor sensed at the first input exceeds the reference rate of discharge signal on the other input;

a timer network responsive to the output of the comparison amplifier for producing a timing pulse of a desired duration; and

means responsive to the timing pulse for delivering relay energizing pulses on separate lines at both the start and end of the timing pulse.

3. A light sensitive control for use in protection of an area comprising a housing shaped and sized to fit within a wall switch socket mounting facing the area to be protected;

a light protection circuit mounted in the housing and having a light responsive variable resistive element oriented to face the area to be protected;

means including a capacitor for establishing a voltage charge on the capacitor;

a discharge circuit coupled to discharge the voltage retained by the capacitor, said discharge circuit including said light responsive element, said light responsive element being coupled to vary the rate of discharge of the capacitor in response to the rate of light exposure of said element; and

means coupled to the discharge circuit for producing an output signal when said rate of discharge exceeds a predetermined value representative of a minimum variation of light incident upon the light sensitive element said output signal producing means including a pulse responsive latching relay mounted to the housing, said relay being provided with output leads for actuation of external devices.

4. The light sensitive control as claimed in claim 3 wherein the output signal producing means further includes a timing circuit for producing a timing pulse upon the incidence of light in excess of a predetermined rate;

and means for producing relay latching and unlatching pulses respectively at the beginning and end of the timing pulse for control of the relay.

5. A light controlled apparatus for generating timed energization of a safety device comprising means including a first light sensing element for generating a control signal representative of the occurrence of daylight and darkness;

a signal gate having an enabling input coupled to the control signal, said signal gate being disabled when the control signal is representative of daylight;

a second light sensing element coupled to the signal gate to produce an output signal therefrom when said second light sensing element is exposed to light;

a timing circuit coupled to the output of the signal gate to generate a timing pulse of predetermined duration when said first light sensing element is exposed to darkness and said second light sensing element is exposed to light;

the timing circuit further including a timing capacitor and a timing resistor coupled to charge the capacitor at a desired controlled rate;

a high input resistance circuit coupled to the timing capacitor and operative below a predetermined charge level of the timing capacitor to produce said timing pulse until the timing resistor has charged the timing capacitor below said predetermined charge level; and

means for producing separate pulses on separate leads at respectively the beginning and end of the timing pulse to energize said safety device, said means for producing said separate pulses further including a pulse responSive latching relay having a pair of control coils for respectively latching and unlatching of the relay, said control coils being coupled to said separate pulses.

6. The light controlled apparatus as claimed in claim 5 wherein the separate pulses producing means further includes a signal inverter driven by the timing pulse and a pair of semiconductor elements coupled to the timing pulse and the signal inverter, said semiconductor elements being coupled to the relay latching and unlatching coils to implement relay control by the timing pulse.