WeatherMon reads ambient temperature, wind direction and wind speed data from a weather station assembly and displays the processed weather data as text on a video monitor or television receiver.

The weather station, jointly developed by Dallas Semiconductor and Texas Weather Instruments, utilises Dallas "1-Wire" bus devices to implement the three weather sensors. The main innovation achieved by the Dallas 1-Wire bus is that it allows transmission of both power and bi-directional data over a single pair of wires, ie one wire and a ground. Each sensor device incorporates a unique serial number that identifies it to the 1-Wire bus. Data transfers are half-duplex and bit sequential over a single pair of wires using short and long time slots to encode the binary 1s and 0s.

The weather station uses a number of different Dallas 1-Wire bus devices. Temperature is measured directly by a DS1820 digital thermometer.

Wind direction is sensed by a weather vane which has a magnet mounted in a rotor attached to its axle. As the wind rotates the vane and attached rotor, the magnet passes over eight magnetic reed switches which are positioned at eight compass points. When a reed switch is closed, its companion DS2401 Silicon Serial Number is connected to the 1-Wire bus, if a DS2407 addressable switch is closed, and the bus master can read its serial number. This number identifies both the switch and the compass point it represents.

Wind speed is measured by wind cups which have two magnets mounted in a rotor attached to its axle. As the wind rotates the cups and attached rotor, the magnets pass over a magnetic reed switch. Reed switch closures are accumulated by a DS2423 counter. The bus master calculates wind speed by calculating the difference between two values stored in the counter, one generated before and the other generated after a clocked interval. The calculation also takes into account the relationship of revolutions per minute to kilometres per hour.

The control box has a simple user interface of one LED indicator of video text display on and four push button switches with functions of toggling the video text on or off, mode selection and "up" and "down". It contains the control board and the video board. Power for the system is derived from a wall transformer. The weather station is connected to the control box by a 30 metre flat telephone-style cable.

The control board comprises a Philips 87C51 microcontroller, Dallas DS1302 Trickle Charge Real Time Clock (RTC) and a 93C56 2048-Bit Serial EEPROM. The RTC provides clock and calendar functions and 31 bytes of static RAM with a super cap backup power supply. The microcontroller collects data from the weather station and RTC at regular intervals and performs the necessary calculation and formatting of the data in preparation for display.

The video board comprises an SGS Thomson STV5730A On-Screen Display Controller (OSD) and a 5 volt linear regulator which provides power for the system. The OSD is a versatile device which, in this application, is used simply to insert up to 11 rows x 28 characters of white opaque text onto a video signal. A system status message, time, date, temperature, wind direction and wind speed are displayed. If there is an input video signal then the OSD functions in mixed mode and the text is overlaid on the video image. If there is no input video signal then the OSD functions in full page mode and the text is overlaid on a uniformly coloured background.