1. Field of the Invention
The present invention relates generally to a very low current, microcontroller operated, wall switch or ceiling mounted, IR motion sensor. More particularly, the subject invention pertains to a multivoltage (120 VAC to 277 VAC) input, low current (leakage current type), microcontroller-based, wall switch or ceiling mounted, IR motion sensor with a latching relay having zero watt load switching capability, provided in a low cost, single PC board design.
In existing lighting systems and also in heating, ventilation, and air conditioning (HVAC) systems, the circuits powering these systems are commonly controlled by wall switches placed in easily accessible locations, such as adjacent to doorways, and the like. Institutions, businesses, offices, and commercial establishments have found that a great deal of power is consumed to light and ventilate rooms and areas which are often unoccupied for relatively long periods of time. Thus it is preferred for energy conservation reasons as well as security purposes that these energy consuming systems be turned on automatically when a room is entered and be turned off a short period of time after a room is completely vacated. To fill this need, occupancy sensors utilizing infrared sensors, ultrasonic sensors, ambient noise sensors, infrared sensors, and the like have been developed in the prior art to detect a human presence in a room and to switch on and off the relatively large loads of the lighting and HVAC circuits.
Frequently, a typical wall light switch receptacle box has been converted for the installation of an occupancy sensor. However, it should be noted that generally only two wires are fed into a typical wall switch box, the hot line wire from the utility power supply to the switch, and the load line wire extending from the switch to the load. Generally, the other side of the load is connected directly to the neutral line wire of the AC power supply without returning to the switch box. Thus the switch box is provided with a hot line to supply the occupancy sensor, but there is no neutral line to connect to the sensor to complete the circuit to the sensor. Extending a third wire from AC neutral to the wall box is an extremely costly and time consuming task, due to the fact that wall and/or ceiling surfaces will frequently need to be breached and reclosed in non-conduit systems, or the wire may need to be pulled through an existing conduit.
In this setting, a conventional circuit employing a voltage transformer and switching relay cannot be utilized, due to the fact that a transformer requires a connection between the hot and neutral lines of the AC utility power supply. A relay for load switching can be used in conjunction with a current transformer to supply circuit power when the load is on and a capacitive coupling circuit can supply circuit power when the load is off. This is costly and takes up considerable space. Another common type of switching system that might be used is an electronic switching circuit comprised of a triac and/or diac device. However, such triac and diac devices create electronic noise and also generate radio frequency interference which can be detrimental to sensitive communications and computer equipment now used in many office and commercial buildings. In addition, these devices are unstable due to the presence of surge currents and voltages as high as 10,000 volts which can occur in electrical systems. These surges can destroy such triac and diac devices. Furthermore, these devices are constantly drawing current and creating heat when the load is switched on. Many consumers are not favorably disposed towards an electrical system which maintains the wall switch box in a state of perpetual heating that is clearly palpable to the touch.
2. Discussion of the Prior Art
Hermans U.S. Pat. No. 4,874,962 discloses an electrical load switching system that is adapted to be used in existing (or new) electrical lighting and HVAC systems without requiring a connection to the neutral line of the AC utility power system. A salient feature of the Hermans system is that it is powered by a connection between the hot leg of the AC utility power supply and the electrical ground which is connected to the wall switch box itself.
The low power switching circuit of Hermans includes a rectifier network connected between the hot leg of the AC utility supply and the ground of the utility supply. A neon lamp and resistors interposed in the rectifier supply limits the current drawn through the rectifier to less than the 500 .mu.a building code and UL limit for current flow to ground. A high sensitivity, dual coil, bistable relay is connected between the hot leg of the AC supply and the load, which is connected to the neutral leg of the AC supply. A capacitor network is connected to the DC output of the rectifier to store sufficient electrical power to operate the relay and a transistor switching network which is connected to deliver power from the capacitor network to the relay upon receipt of a trigger signal. A smart switch such as an area occupancy sensor is connected to the transistor switching network to provide the trigger signal to cause the relay to switch AC power to the load.