I am currently using the REVC sensor from Modern device to measure the wind speed and temperature for a project.
While using the sensor with an external 5V power supply, I started to get very strange values for both the temperature and the wind speed ( temperatures of about -23C at 25C and wind speeds of about 500m/s when there was no wind ). I made use of the code provided on the website and the issue continued even when I switched from the external power supply to the 5V from the Arduino.
Link to sensor: Wind Sensor Rev. C – Modern Device
code used:
/* Modern Device Wind Sensor Sketch for Rev C Wind Sensor
This sketch is only valid if the wind sensor if powered from
a regulated 5 volt supply. An Arduino or Modern Device BBB, RBBB
powered from an external power supply should work fine. Powering from
USB will also work but will be slightly less accurate in our experience.
When using an Arduino to power the sensor, an external power supply is better. Most Arduinos have a
polyfuse which protects the USB line. This fuse has enough resistance to reduce the voltage
available to around 4.7 to 4.85 volts, depending on the current draw.
The sketch uses the on-chip temperature sensing thermistor to compensate the sensor
for changes in ambient temperature. Because the thermistor is just configured as a
voltage divider, the voltage will change with supply voltage. This is why the
sketch depends upon a regulated five volt supply.
Other calibrations could be developed for different sensor supply voltages, but would require
gathering data for those alternate voltages, or compensating the ratio.
Hardware Setup:
Wind Sensor Signals Arduino
GND GND
+V 5V
RV A1 // modify the definitions below to use other pins
TMP A0 // modify the definitions below to use other pins
Paul Badger 2014
Hardware setup:
Wind Sensor is powered from a regulated five volt source.
RV pin and TMP pin are connected to analog innputs.
*/
#define analogPinForRV 1 // change to pins you the analog pins are using
#define analogPinForTMP 0
// to calibrate your sensor, put a glass over it, but the sensor should not be
// touching the desktop surface however.
// adjust the zeroWindAdjustment until your sensor reads about zero with the glass over it.
const float zeroWindAdjustment = .2; // negative numbers yield smaller wind speeds and vice versa.
int TMP_Therm_ADunits; //temp termistor value from wind sensor
float RV_Wind_ADunits; //RV output from wind sensor
float RV_Wind_Volts;
unsigned long lastMillis;
int TempCtimes100;
float zeroWind_ADunits;
float zeroWind_volts;
float WindSpeed_MPH;
void setup() {
Serial.begin(57600); // faster printing to get a bit better throughput on extended info
// remember to change your serial monitor
Serial.println("start");
// put your setup code here, to run once:
// Uncomment the three lines below to reset the analog pins A2 & A3
// This is code from the Modern Device temp sensor (not required)
//pinMode(A2, INPUT); // GND pin
//pinMode(A3, INPUT); // VCC pin
//digitalWrite(A3, LOW); // turn off pullups
}
void loop() {
if (millis() - lastMillis > 200){ // read every 200 ms - printing slows this down further
TMP_Therm_ADunits = analogRead(analogPinForTMP);
RV_Wind_ADunits = analogRead(analogPinForRV);
RV_Wind_Volts = (RV_Wind_ADunits * 0.0048828125);
// these are all derived from regressions from raw data as such they depend on a lot of experimental factors
// such as accuracy of temp sensors, and voltage at the actual wind sensor, (wire losses) which were unaccouted for.
TempCtimes100 = (0.005 *((float)TMP_Therm_ADunits * (float)TMP_Therm_ADunits)) - (16.862 * (float)TMP_Therm_ADunits) + 9075.4;
zeroWind_ADunits = -0.0006*((float)TMP_Therm_ADunits * (float)TMP_Therm_ADunits) + 1.0727 * (float)TMP_Therm_ADunits + 47.172; // 13.0C 553 482.39
zeroWind_volts = (zeroWind_ADunits * 0.0048828125) - zeroWindAdjustment;
// This from a regression from data in the form of
// Vraw = V0 + b * WindSpeed ^ c
// V0 is zero wind at a particular temperature
// The constants b and c were determined by some Excel wrangling with the solver.
WindSpeed_MPH = pow(((RV_Wind_Volts - zeroWind_volts) /.2300) , 2.7265);
Serial.print(" TMP volts ");
Serial.print(TMP_Therm_ADunits * 0.0048828125);
Serial.print(" RV volts ");
Serial.print((float)RV_Wind_Volts);
Serial.print("\t TempC*100 ");
Serial.print(TempCtimes100 );
Serial.print(" ZeroWind volts ");
Serial.print(zeroWind_volts);
Serial.print(" WindSpeed MPH ");
Serial.println((float)WindSpeed_MPH);
lastMillis = millis();
}
}