Infrared indoor-outdoor thermometer system
Indoor-outdoor thermometer systems for measuring an outdoor temperature and conveniently displaying the outdoor temperature on an indoor display are known in the art. Conventionally, these systems utilize a wired transmission medium between the indoor and outdoor components. These conventional systems suffer the disadvantage of requiring a wire with a temperature sensing device to penetrate an opening in a window or outside wall to measure the outside temperature. The inconvenience of having to create and close off such an opening limits the practicality of such a thermometer.
Other prior art systems are disclosed wherein sensed temperature data is transmitted optically to a remote receiver. U.S. Pat. No. 4,848,923, issued to Ziegler et al., teaches a measurement system which converts sensed parameter signals into light pulses which are transmitted to remote evaluation units. The Ziegler system employs a quartz measuring transducer coupled to an oscillator wherein the resulting frequency of oscillation is representative of the value of the sensed parameter.Therefore, Ziegler does not teach a simple wireless system that can be adapted for practical use in an indoor-outdoor thermometer application. Moreover, Ziegler does not teach a low power consumption system compatible with a long lasting low cost battery such as a lithium type cell.
To alleviate some of the problems and drawbacks of wired thermometer systems, wireless indoor-outdoor thermometer systems employing radio frequency waves have been developed. U.S. Pat. No. 4,608,565 to Sakamoto discloses an indoor-outdoor thermometer including a temperature transmitting unit and receiving unit disposed on opposite sides of an exterior wall or window.Moreover, the use of radio frequency transmission is not consistent with low power consumption and hence, is not conducive to the use of a long lasting and low cost battery such as a lithium type battery. Thus, a homeowner cannot avoid the inconvenience and cost of frequent battery replacement.
Thus, there is a need for an indoor-outdoor thermometer system employing a physically small outdoor unit mounted to, or in proximity to, an outer window surface to transmit outdoor temperature data to an indoor display unit mounted on any conveniently chosen indoor room location. There is also a need for such a thermometer to be of low power consumption design for long lasting maintenance free operation. There is a need for such a thermometer to provide accurate and reliable temperature measurements in a noisy environment with temperature data updated every few minutes.
The present invention relates to an indoor-outdoor thermometer system employing a wireless free space infrared telemetry link. A first unit measures a first temperature at a first location and transmits coded data indicative of the first temperature to a second unit, where it is displayed. The first unit may be an outdoor unit that is mounted on or in proximity to the exterior of a window. Housed within the first unit is a temperature transducing means, first conversion means coupled to the transducing means, modulation means coupled to the first conversion means and infrared transmission means coupled to the modulation means.The infrared data is detected by detection means within the second unit to provide detected data pulses indicative of the first temperature to a second conversion means. The second conversion means converts the detected data pulses to numerical data representative of the first temperature to a display, where it is displayed.
The first and second units may be equipped with interval timing means whereby temperature data is measured, transmitted and detected only at predetermined periodic time intervals. This technique results in a drastic reduction of power consumption by the first and second units, thereby affording the use of long lasting maintenance free lithium type batteries as the power source.
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