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The scope
for this project was that the local paraglider pilots wanted a
cheap and maintenance free weather station that could tell them
about the current wind condition at their favourite flying site.
They had access to a PSTN line at the clubhouse by the landing
field. The take off is on a mountaintop 300m above the landing.
A mobile phone weather station was considered but it needed an
expensive solar cell to charge the backup battery. It is also
more expensive to call a mobile phone than a PSTN telephone. The
solution was to use the PSTN line and have 2 units, both based
on a MSP430F148, and a wireless link between them. The first unit
(TX unit) is placed on the mountaintop. It consists of a MSP with
some additional electronics, a Davis anemometer, a battery, a
cheap solar cell and a walkie-talkie (27MHz AM) transmitter. The
second unit (RX unit) is placed inside the clubhouse and consists
of a board with a MSP, a telephone answer machine, a walkie-talkie
receiver and an AC adapter. The TX unit logs the wind speed and
direction for the last 15 minutes. Every 30 seconds it turns the
transmitter on and sends a FSK encoded 13-byte package to the
receiver at a speed of 300bps. The quality of the package is ensured
by a CRC-16 word, which is checked at the receiver end. The package
consists of wind data: maximum and minimum direction and speed
both present and mean values and also sun intensity.
Block
Diagram
 
Arne Jan
Dahl
Hommesaak, Norway
ajdahl@online.no
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