# BrentT

Member Since: January 6, 2010

Country: United States

• Re: Wind Speed per closed contact count …
I think I’ve answered my own question from back on April 27th regarding the Wind Speed per closed contact count. Today I pulled up some info on cup style Anemometers. According to the original inventor of the cup Anemometer, the cup velocity should be ~1/3 that of the wind. That gives an approximate value of 1.6 mph for this Anemometer to close a contact once per second (with two closed contacts per revolution).
I will be using the datasheet’s value of 1.492 mph per 1 closed contact per second.
To N1VG – would you please confirm this?

• In addition, I have modified Steve’s code for the Wind Direction. I used the 10k resistor as suggested from the datasheet. You’ll see I am outputting a float rather than a string for my needs.
// Find vane direction.
void calcWindDir() {
#define NUMDIRS 16
float adc[NUMDIRS + 1] = {0.0, 0.365, 0.43, 0.535, 0.76, 1.045, 1.295, 1.69,
2.115, 2.59, 3.005, 3.255, 3.635, 3.94, 4.33, 4.7, 5.0};
//float expectedVoltages[NUMDIRS] = {0.32, 0.41, 0.45, 0.62, 0.9, 1.19, 1.4, 1.98
// 2.25, 2.93, 3.08, 3.43, 3.84, 4.04, 4.62, 4.78}
//char *strVals[NUMDIRS] = {“ESE”,“ENE”, “E”,“SSE”, “SE”,“SSW”, “S”, “NNE”,
// “NE”,“WSW”,“SW”,“NNW”,“N”,“WNW”, “W”, “NW”};
float directions[NUMDIRS] = {112.5, 67.5, 90, 157.5, 135, 202.5, 180, 22.5,
45, 247.5, 225, 337.5, 0, 292.5, 270, 315};
//byte dirOffset=0;
unsigned int val;
float voltage;
byte x;
voltage = (float)val / 1024.0 * 5.0;
for (x=0; x= adc[x]) && (voltage < adc[(x+1)]))
break;
}
//x = (x + dirOffset) % NUMDIRS;
windDir = directions[x];
}

• Domos: _ A wind speed of 1.492 MPH (2.4 km/h) causes the switch to close once per second. But I do not understand, I tested the anemometer and I have 2 contacts per revolution. Can you confirm the number of contacts per revolution ?_
I have the same question as Domos. The values given in the datasheet appear to give wind speeds that are double. I checked my readings against a 10-yr old Kestrel 3000 hand held meter, and the wind speeds were ½. I have adjusted my values to 0.746 mph / count, where the counting is done on the Falling value, or “attachInterrupt(INTERRUPT_ANEMOMETER, countAnemometer, FALLING)”;
Has anyone else found this to be true???
To attempt to answer some dimensional questions with the model I received: 1) Tube diameter = 0.795" or 20.4mm. 2) Distances from center of tube to centers of Anemometer and Wind Dir: ~5". 3) Distances from center of tube to max distance out for a) Anemometer: ~8.5", b) Wind Dir: ~9", and c) Rain Gauge: ~9.1".
Steve, thank you for posting your code!! Very helpful.

• This board has a voltage regulator for Vin to the chip. Are the logic levels converted down from 5V to the 1.7V to 3.6V required I/O voltage range for the chip?

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