WX #175 - Interfacing with a Fascinating Anemometer and Wind Vane

Fascinating Electronics sells two types of anemometers, regular and heavy duty, and a wind vane. The price of the regular duty anemometer and the wind vane are nominally $50.00 each and a connecting Tee is about $15.00

The Fascinating hardware is very well thought out and it is of very high quality; plastic that will last, anodized aluminum and stainless steel hardware. It was the best I have found and yet, the least inexpensive by far. Fascinating is unique in that it offers the hardware in kit form.

Note. Fascinating also offers humidity and temperature sensors. These are not compatible with the WX #175 kit.


The rotating assembly provides a magnet (or magnets) which open and close a fixed reed relay. The reed relay thus provides dry closures at a rate which is proportional to the wind speed. This might be interfaced with the WX #175 counter input as illustrated in Figure #7 of the WX #175 Assembly Documentation. Reed relays tend to bounce when switched and thus a debounce filter consisting of a series 10K resistor and a shunt capacitor is necessary to eliminate multiple counts. I include a 10K resistor and a 0.1 uFd capacitor wit the WX #175 kit.

Fascinating indicates the wind speed in miles per hour is the number of counts in 1.5 seconds. Thus, you might use the command "C3" so as to measure the number of counts over a three second period and then divide the result by two.

Wind Vane

See Figure #9 of the WX #175 Assembly Documentation.

Fascinating uses a special dual wiper 5K Ohm potentiometer with a single shaft with no stops. The wiper area of the potentiometer is 270 degrees leaving 90 degrees of "dead zone" where the wiper is open. However, the two wipers are oriented at 90 degrees relative to one another. Thus, when one wiper is in the dead zone (ADC reading near zero), the value of the second wiper may be used. Thus, with one wiper connected to WX #175 input ANALOG 1 and the other to ANALOG 2, ADC measurements may be performed using the "A1" and "A2" commands. .

The angles of the two wipers may be calculated as;

angle_1 = adval_1 / 4096.0 * 270.0
angle_2 = adval_2 / 4096.0 * 270.0 + 90.0

Thus, the relative angle is calculated as;

	if (angle_1 > 10.0)
	   relative_angle = angle_1;

	   relative_angle = angle_2;

I used to have many of these special potentiometers laying around, but they have been used in various student projects and of this writing, I do not have a unit to test. Thus, whether that is plus 90.0 or minus 90.0 degrees is a guess. However, it is easy enough to try a plus 90.0 and if it is incorrect, correct my error and modify this to minus 90.0.

Note that this is a relative angle.

I have been married for 35 years and the most serious strains have been when I was up on the roof or a ham radio tower tweaking a capacitor asking my wife for a SWR or noise bridge reading. It can sure ruin a nice Sunday with what starts as communicating shouts quickly lead to rather angry shouts.

Preserve your marriage. Simply mount the wind vane and then add whatever fudge is required;

absolute_angle = relative_angle + fudge;
This may well mean that some angles are 360 degrees or greater. This can be easily corrected;
if (absolute_angle => 360.0)
   absolute_angle = absolute_angle - 360.0;