This device is intended to replace the original anemometer supplied with the weather station. This is the wind speed and direction sensor only. It must connect with the weather station sensor suite.
last updated: October 20, 2010

Objective

This project is to inspire a team of forum members to design and build an anemometer and direction vane. The construction details will be shared so that anyone can build the device using common parts. The device should be compatible with Davis systems, easily repairable, inexpensive, be reliable, and have a professional appearance.
Some owners of personal weather stations wish to have a wind sensor they can repair. If a PWS owner builds this wind sensor, they can repair it when needed.
The design isn't completed yet. The wind vane parts fit and the circuit works. The reed switch closes/opens in the vicinity of a changing magnetic field. The anemometer cups mounting design is not completed.
Considerating adding an anti-icing scheme.

Design
anemometer and vane schematic

PHYSICAL STRUCTURE
The physical framework of the device is made from plumbing copper parts. These common items are readily available from most hardware stores. Most is 1/2 inch copper fittings. Finish on the copper is the owner's personal preference.
The most difficult, and not solved yet, design is how to mount the anemometer cups shaft and bearings. Some ideas are being tried.
Another issue to solve is preventing rain entering the hub below the anemometer cups on the horizontal style. If the cups are above the hub, the open hub allows rain to enter.
ELECTRONICS CIRCUIT
The circuit is compatible with the Davis VP2 weather station. It uses a potentiometer to sense the wind direction vane position. A magnetic reed switch opens and closes once per revolution of the anemometer cups. The magnet that operates the switch is mounted in the cup assembly.
A generic perforated circuit board can be used to mount the reed switch and the other components if desired. A printed circuit board is available for purchase. All electronic parts used in this design are available from electronic parts suppliers.
The potentiometer type is critical. It must be a continuous rotation 360º with no mechanical stop. The gap in the resistance element should be as narrow as possible. The Bourns 6639 meets these needs. It should be 20K. The 6639 type was chosen for its 1/4" shaft diameter to match the wind vane.
The other resistors aren't critical in value or type. The 1/8 Watt size fits the hole spacing in the circuit board. The board has a pattern that will allow 0805 size chip resistors to be mounted instead of the axial type if desired.
The two 47 Ohm resistors are for safety in case someone applies power to the red and black wires. The resistors will protect the reed switch from damage. The 909K resistor value is not critical. It "pulls" the direction green wire to the + voltage value during the time the potentiometer wiper is between the two ends of the resistance element. It prevents the direction wire from 'floating'.


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Parts List
 
vertical style
horizontal style
ITEM MOUSER STOCK NUMBER DESCRIPTION QUANTITY PRICE EACH TOTAL
1   direction vane 1    
2 652-6639S-1-203
Bourns 6639 20K potentiometer 360º turn no stop 1 12.09 12.09
3
hub (NOT AVAILABLE YET) 1    
4
.125" shaft 1.60" long (NOT AVAILABLE YET) 1    
5 R2ZZ (from gotbearings) .125" bore, .375" diameter bearing 2 2.95 5.90
6   anemometer cups
1    
7   copper 90º Elbow 3/4" x 1/2"

2    
8   copper Tee 1/2" x 1/2" x 1/2"

1    
9   copper pipe 1/2" x 8"

1    
10   copper pipe 1/2" x length to fit

1    
11   copper Tee "3/4X 3/4" X 1/2"

1    
12   copper pipe 1/2" x 2"

1    
13   copper 45º Elbow 1/2" x1/2"
2    
    circuit board 7/8" diameter with center hole 1    
           
  876-KSK-1A35-1015 reed switch
1 .69 .69
  71-RN55D-F-909K 909K 1/8W axial lead resistor 1 .19 .19
  71-RN55D-F-47.5 47.5 Ohm axial lead resistor 2 .10 .20
           
  note 1 buy 2 reed switches, you'll break the first one      
  note 2 Use 26 gauge stranded hook up wire in three different colors. 6 inches for vertical style    
      24 inches for horizontal style    
  note 3 use perf board or send a personal message to ________ for details on a printed circuit board      
           
           
Old Parts
3 Davis anemometer hubs
 

3 Davis anemometer hubs

   
end view showing anemometer shaft, bearing and reed switch pcb
 

end view showing anemometer shaft, bearing and reed switch pcb

   
end view showing vane pot
 

This end view shows the direction vane pot shaft.

   
showing pot removed from hub
 

Some pots are glued in. This is a hub that the pot wasn't glued and just pressed into the hub.

   
Another hub that was sawed to remove the components.
 

Another hub that was sawed to remove the components.

   
inside view of hub that was sawed open
 

inside view of hub that was sawed open, brass bushing is visible

   
anemometer shaft , two retaining ring clips, bearing and brass bushing
 

anemometer shaft , two retaining ring clips, bearing and brass bushing

   
two anemometer pc boards, reed switches, and direction potentiometer
 

Two anemometer pc boards, reed switches, and direction potentiometer. The 909K resistor is mounted on terminals on the back of the potentiometer.

   
References
Data Sheets  
spec sheets  
KSK-1A35-1015 Meder reed switch 10.5 mm  
6639S-1-203 20K 360 Bourns potentiometer