Weather station


Posted on Sep 5, 2012

This 1-Wire MicroLAN [1] uses a capacitor and diode half-wave rectifier to provide parasitic power from the data line for the station's various sensors and to transfer data (see Figure 1). Each sensor has a unique serial number that identifies it to the bus. The station is controlled by a PC or microprocessor executing Touch Memory Executive (TMEX) software. Data transfers are half-duplex and bit sequential over a single twisted pair using short and long time slots to encode the binary 1s and 0s.


Weather station
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Weather station - image 1
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Weather station - image 2
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Wind Direction Magnetically activated reed switches were selected as the wind sensors for several reasons. They do not require power to operate. Because they are neither motion nor rate dependent, they can measure static conditions. They do not require signal conditioning. And they have a very high impedance in the open state and negligible impedance (150 m) when closed. The basic weather station measures wind speed and direction, ambient temperature, and rainfall totals (see Figure 2). The package can be augmented with humidity, barometric pressure, and other weather sensors simply by connecting the sensor to the cable at the desired position and adding the appropriate software. Another option is to connect several weather stations to the same 1-Wire communication link for cost-effective measurement of laminar air flow patterns and other climatic parameters. Interestingly, reed switches are normally rated as failed or end-of-life when the on resistance of the switch reaches 1 or 2 when operated at rated power level. A reed switch can operate over 100 million or more cycles at 50 V/100 mA levels or higher before failure. 1-Wire devices, which run at 5 V/4 mA, present almost no load, however, and can work with on resistance values of up to 100 . The functional lifetime of a reed switch in a 1-Wire environment such as the weather station is therefore much greater. Ongoing tests on the weather station show no degradation...




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