Solar Powered Mini-Weather Station

[Petjepet]

@gigi I know but in your breadboard picture the now mentioned V output is connected directly to ground. :smirk:

[gigi]

@Petjepet I Know, thank

on board as I did your chart

Thank

[peerkersezuuker]

Back to the weather station.
I was having problems reporting wind speed to domoticz (in hardware my sensor was listed, but there was no device creation)
After a question on their forum, i learned tha i had to implement gust and direction to the sensor becaus Domoticz is aspectiong these to before it vreates a device.
I had to remove the rainrate because the sketch was getting to big.
Here is the latest sketch i am using :

    #include <SPI.h>
    #include <MySensor.h>  
    #include <dht.h>
    #include <BH1750.h>
    #include <Wire.h> 
    #include <Adafruit_BMP085.h>
    #include <MySigningAtsha204.h>
    
    #define CHILD_ID_HUM 0
    #define CHILD_ID_TEMP 1
    #define CHILD_ID_LIGHT 2
    #define CHILD_ID_BARO 3
    #define CHILD_ID_BTEMP 4
    #define CHILD_ID_WINDSPEED 5
    #define CHILD_ID_RAIN 6
    
    #define MESSAGEWAIT 500
    #define DIGITAL_INPUT_RAIN_SENSOR 3
    #define HUMIDITY_SENSOR_DIGITAL_PIN 5
    #define ENCODER_PIN 2
    #define INTERRUPT DIGITAL_INPUT_RAIN_SENSOR-2

    const int  windSpeedPin = 2; // contact on pin 2 digital
    int windSpeedPinCounter = 0; // impuls counter
    int windSpeedPinStatus = 0; // actual impuls
    int windSpeedPinStatusAlt = 0; // oude Impuls-Status
    unsigned long windmeterStart;
    unsigned long windmeterStartAlt = 0;
    int windSpeed; // Variable voor Wind Speed
    int beaufort = 0; // Variable Wind in Beaufort
    const int windmeterTime = 10000;
    //float knoten = 0.0;
    //float wind = 0.0;
    unsigned int knoten;
    unsigned int wind;
   
    boolean metric = false;
    int altitude = 16; // meters above sealevel
    float lastBmpTemp = -1;
    float lastPressure = -1;
    float lastHum = -1;
    float lastTemp = -1;
    double temp;
    double hum;
    int BATTERY_SENSE_PIN = A0;
    int lastRainValue = -1;
    int nRainVal;
    boolean bIsRaining = false;
    String strRaining = "NO";
    int lastBatteryPcnt = 0;
    int updateAll = 60;
    int updateCount = 0;
    uint16_t lastLux;
    // unsigned long SLEEP_TIME = 60000;
    unsigned long SLEEP_TIME = 600;
    int batteryBasement = 800;
    float batteryConstant = 100.0 / (1023 - batteryBasement);

    MyTransportNRF24 radio;  // NRFRF24L01 radio driver
    MyHwATMega328 hw; // Select AtMega328 hardware profile
    MySigningAtsha204 signer(true); // Select HW ATSHA signing backend
    
    Adafruit_BMP085 bmp = Adafruit_BMP085();
    BH1750 lightSensor;
    dht DHT;
    MySensor gw(radio, hw, signer);

    MyMessage msgHum(CHILD_ID_HUM, V_HUM);
    MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
    MyMessage msgLux(CHILD_ID_LIGHT, V_LIGHT_LEVEL);
    MyMessage msgBtemp(CHILD_ID_BTEMP, V_TEMP);
    MyMessage msgPressure(CHILD_ID_BARO, V_PRESSURE);
    MyMessage msgWindSpeed(CHILD_ID_WINDSPEED, V_WIND);
    MyMessage msgWGust(CHILD_ID_WINDSPEED, V_GUST);
    MyMessage msgWDirection(CHILD_ID_WINDSPEED, V_DIRECTION);   
    MyMessage msgRain(CHILD_ID_RAIN, V_TRIPPED);

    void setup()  
    {
      analogReference(INTERNAL);
      gw.begin(incomingMessage, 3, true);  
      //dht.setup(HUMIDITY_SENSOR_DIGITAL_PIN); 
      bmp.begin();
      gw.sendSketchInfo("Weather Sensor", "1.0");
      gw.present(CHILD_ID_HUM, S_HUM, "WS Humidity");
      gw.present(CHILD_ID_TEMP, S_TEMP, "WS Temperature");
      gw.present(CHILD_ID_LIGHT, S_LIGHT_LEVEL, "WS Lux");
      gw.present(CHILD_ID_BARO, S_BARO, "WS Pressure");
      gw.present(CHILD_ID_BTEMP, S_TEMP, "WS P Temperature");
      gw.present(CHILD_ID_WINDSPEED, S_WIND, "WS Windspeed");
      gw.present(CHILD_ID_RAIN, S_MOTION, "WS Rain");

      pinMode(DIGITAL_INPUT_RAIN_SENSOR, INPUT);
      lightSensor.begin();
      metric = gw.getConfig().isMetric;
    }
    
    // Wind Meter https://github.com/chiemseesurfer/arduinoWeatherstation/blob/master/weatherstation/weatherstation.ino
    
    float windmeter()
    {
        windmeterStart = millis(); // Actual start time measuringMessung
        windmeterStartAlt = windmeterStart; // Save start time
    
        windSpeedPinCounter = 0; // Set pulse counter to 0
        windSpeedPinStatusAlt = HIGH; // Set puls status High
    
        while ((windmeterStart - windmeterStartAlt) <= windmeterTime) // until 10000 ms (10 Seconds) ..
        {
            windSpeedPinStatus = digitalRead(windSpeedPin); // Read input pin 2
            if (windSpeedPinStatus != windSpeedPinStatusAlt) // When the pin status changed
            {
                if (windSpeedPinStatus == HIGH) // When status - HIGH
                {
                    windSpeedPinCounter++; // Counter + 1
                }
            }
            windSpeedPinStatusAlt = windSpeedPinStatus; // Save status for next loop
            windmeterStart = millis(); // Actual time
        }
    
        windSpeed =  ((windSpeedPinCounter * 24) / 10) + 0.5; //  WindSpeed - one Pulse ~ 2,4 km/h, 
        windSpeed = (windSpeed / (windmeterTime / 1000)); // Devided in measure time in seconds
        Serial.print("wind Speed : ");
        Serial.println(windSpeed);    
        knoten = windSpeed / 1.852; //knot's
    
        return windSpeed;
    }
    
    void loop()      
    {
      updateCount += 1;
      if (updateCount == updateAll) {
        lastTemp = -1;
        lastHum = -1;
        lastLux = -1;
        lastBmpTemp = -1;
        lastPressure = -1;
        lastRainValue = -1;
        lastBatteryPcnt = -1;
        updateCount = 0;
      }
      delay(2000);
      int chk = DHT.read22(HUMIDITY_SENSOR_DIGITAL_PIN);
      temp = DHT.temperature;
             //Serial.print("Temperature DHT :");
             //Serial.println(temp);
      if (isnan(temp)) {
          lastTemp = -1;
      } else if (temp != lastTemp) {
        lastTemp = temp;
        if (!metric) {
          temp = temp * 1.8 + 32.0;
        }
        gw.send(msgTemp.set(temp, 1));
        }
      hum = DHT.humidity;
      if (isnan(hum)) {
          lastHum = -1;
      } else if (hum != lastHum) {
          lastHum = hum;
          gw.send(msgHum.set(hum, 1));
      }
      uint16_t lux = lightSensor.readLightLevel();
      if (lux != lastLux) {
          gw.send(msgLux.set(lux));
          lastLux = lux;
      }
      float pressure = bmp.readSealevelPressure(altitude) * 0.01;
      float bmptemp = bmp.readTemperature();
      if (!metric) {
        bmptemp = bmptemp * 1.8 + 32.0;
      }
      if (bmptemp != lastBmpTemp) {
        gw.send(msgBtemp.set(bmptemp,1));
        lastBmpTemp = bmptemp;
      }
      if (pressure != lastPressure) {
        gw.send(msgPressure.set(pressure, 0));
        lastPressure = pressure;
      }
      
      bIsRaining = !(digitalRead(DIGITAL_INPUT_RAIN_SENSOR));
      if(bIsRaining){
          strRaining = "YES";
      }
      else{
          strRaining = "NO";
      }
  
      //Serial.print("Raining?: ");
      //Serial.print(strRaining);  
      //Serial.print("\t Moisture Level: ");
      //Serial.println(nRainVal);
      //http://henrysbench.capnfatz.com/henrys-bench/arduino-sensors-and-input/arduino-rain-sensor-module-guide-and-tutorial/

      gw.send(msgRain.set(bIsRaining, 1));

      wind = windmeter();
      Serial.print("Wind : ");
      Serial.println(wind);
      int wdirection = 1;
      int wgust = 1;
      gw.send(msgWindSpeed.set(wind, 1));
      gw.send(msgWGust.set(wgust, 1));
      gw.send(msgWDirection.set(wdirection, 1));
      
      int sensorValue = analogRead(BATTERY_SENSE_PIN);
      int batteryPcnt = (sensorValue - batteryBasement) * batteryConstant;
      if (lastBatteryPcnt != batteryPcnt) {
        gw.sendBatteryLevel(batteryPcnt);
        lastBatteryPcnt = batteryPcnt;
      }
      gw.sleep(SLEEP_TIME);
   }

    void incomingMessage(const MyMessage & message) {
    // We only expect one type of message from controller. But we better check anyway.
     if (message.isAck()) {
       Serial.println("This is an ack from gateway");
     }
    }

regards Peer

[Elfnoir]

Hi,
It means that there is no possibility to implement wind speed on this weather station... ok.
I've just received the good Li-Ion charging component, I can continue with the construction!

I'll post if I will be facing for some trouble, or when it will be finished.

[AffordableTech]

@Salmoides - I must congratulate you on a very neat and professional build.

I'm not sure if you are still hanging around this forum but even if you aren't, others may find the following suggestion helpful.

@Salmoides said*:

With it [the rain detector] I get 0.98 mA [drain] during the gw.sleep command

There is a very easy, but often overlooked, method to disable sensors to reduce battery drain that requires no additional components. Because the sensor draws approximately 1ma, that is well within the 'drive' capacity of an Arduino output pin (which is about 20ma). So, all you need to do is wire the "+" power pin of the rain sensor to a spare output pin and "digitalWrite(pin,HIGH)" to turn it on and "digitalWrite(pin,LOW)" to turn it off.

IMPORTANT: You should check the specs of the processor you are using to make sure the I/O pin can 'drive' or 'source' more than the required current of the sensor you wish to switch. I'd suggest allowing a 50% safety margin.

Paul

[5546dug]

@AffordableTech

Looks like a feasible idea, as my stn does consume all the battery on bad days, and yes I needed the diode between the solar and controller to get to the right voltage

cheers doug

[Renard]

Hello, it a nice job
I am french so I beg your pardon for my poor English
Can you , please show me how the lipo and the solar cell are connected and how the arduino is powered by the little shield (Charger Board ) at the right of picture over the DHT ?
Thanks

[bisschopsr]

@gigi: Besides the already adressed error in the Fritzing I have anaother question. In the diagram there is a charge controller for 12V. The original design in this threat uses a 5V charging module. What module are you using or planning to use?
Thanks Ralph

[Elfnoir]

@Renard : Bonjour! Je fais le raccordement cette semaine j'espère, je galère sur la déclaration dans Domoticz et l'étalonnage pour controler la charge de la batterie, mais je dirais:

• OUT+ et - sur RAW et GND de l'Arduino
• B+ B- à la batterie
• "+ et -" au panneau solaire, c'est ce qu'il me semble sur les photos.

@bisschopsr : Hi, There is no charge controler 5 or 12 volts. On my Fritzing to understand better the scheme (Post #70), I draw batteries and solar panel, but Fritzings following are with 12volts charger, I don't know why. If you purchased a solar lamp, it's to avoid 5 or 12volts charger and use the sun ;-)

[Renard]

Merci pour la réponse
C 'est donc l'arduino qui gère la décharge..
Je vais donc mettre "Arduino Compatible Solar Charger shield -LiPo rider" a la place ...

Thanks for answer
It is the arduino wich control the discharge
I put "Arduino Compatible Solar Charger shield -LiPo rider" without control of lipo capacity

[bisschopsr]

Thanks for the anwer @Elfnoir. I looked back at your schedule and there is some logic between the solar panel, the batteries and the other components (as the power consumers). That logic in the middle is what I refered to as charge controller. I would like to know what part this is.
Thanks again.
Ralph

[Elfnoir]

@Renard c'est bien l'arduino qui gère la décharge et envoi l'info à Domoticz; c'est pour cela que tu dois étalonner le min/max avec le potentiomètre
it is the Arduino which manages the discharge and send the info to Domoticz ; that's why you have to calibrate the min / max with the potentiometer

@bisschopsr If I well understand your question, the module which take the solar power to charge the battery with providing in the same time power to the arduino, and provide power of the battery to the arduino when there is no sun or at night: it's the Lipo Ride. There is no monitoring from the Arduino to the Lipo, but the Arduino read the level of voltage coming from the battery and send it to Domoticz.
Do I understand well your question please?

[bisschopsr]

@Elfnoir You understood the question correct :). That was the answer I was looking for. So your battery is something like a 3.7V LiOn?
Thanks again
Ralph

[Elfnoir]

@bisschopsr yes, the battery inside the “16 LED Solar Power Motion Sensor Security Lamp Outdoor Waterproof Light” (http://www.ebay.com/itm/271693521438) is 3.7v 800mAh.

[bisschopsr]

@Elfnoir Thank you very much. I found a local LED lamp with 3.6V 600mAh NiMh battery. I'm going to try and make a simular solution from that one.

[Petjepet]

@Salmoides I built this weather station (exactly as decribed above in the initial message) and have some problems with the radio when going about 15 meters from the gateway.
I have several other nodes on similar distance working just fine.

I guess the metal top of the case (where the solar panel is in) is causing the issue. Is there a way to change that? Maybe an additional antenna wire (how)?

[bisschopsr]

@Petjepet The metal is definitely influencing the radio performance. It’s 2.4 GHz like the home wifi signal, so you might understand the impact if you compare these two. A solution to use a radio with an external antenna that can be placed outside the metal case. There is a radio with ext. antenna available, you might need an additional extension cable of say 15-30 cm. Does this help.

Regards,

Ralph

[Petjepet]

@bisschopsr That must be the same one I use for the gateway with the external antenna.
I also saw once a wire connected to the standard radio but can't recall where I saw that.

[bisschopsr]

@Petjepet Yes, you are probably using this version for the GW (I know I am :-)). I have also see people hacking the original module by attaching a wire antenna instead of the on board printed antenna. The advantage of the other antenna based board is, you can actually bring the antenna to the outside. Something more difficult to do with a wire hack.

[mrc-core]

I have been adapting this mini-weather station code to he API 2.0 and add it the battery sensor. Here's my first attemp

// Enable debug prints to serial monitor
#define MY_DEBUG 

// Enable and select radio type attached
#define MY_RADIO_NRF24
//#define MY_RADIO_RFM69

#define MY_NODE_ID 2
#define MY_PARENT_NODE_ID  0
#define MY_PARENT_NODE_IS_STATIC

#include <SPI.h>
#include <MySensors.h>  
#include <DHT.h>
#include <BH1750.h>
#include <Wire.h> 
#include <Adafruit_BMP085.h>

#define round(x) ((x)>=0?(long)((x)+0.5):(long)((x)-0.5))

#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1
#define CHILD_ID_LIGHT 2
#define CHILD_ID_BARO 3
#define CHILD_ID_BTEMP 4
#define CHILD_ID_WINDSPEED 5
#define CHILD_ID_BATTERY 6
    
#define MESSAGEWAIT 500
#define DHT_DATA_PIN 3          // Pin 3 digital = DHT11 or DHT12
#define windSpeedPin 4          // Pin 4 digital = Anenometer
#define SENSOR_TEMP_OFFSET 0
#define STABILIZATION_TIME 500  // Let the sensor stabilize 0.5 seconds before reading

static const uint8_t FORCE_UPDATE_N_READS = 10;
static const uint64_t UPDATE_INTERVAL = 60000;

#define BATTERY_FULL 7400 // 3,000 millivolts when battery is full (assuming 2xAA)
#define BATTERY_ZERO 2800 // 1,700 millivolts when battery is empty (reqires blown brownout detection fuse, use 2,800 otherwise)

const float ALTITUDE = 162; // <-- adapt this value to your own location's altitude.

int windSpeedPinCounter = 0;        // impuls counter
int windSpeedPinStatus = 0;         // actual impuls
int windSpeedPinStatusAlt = 0;      // oude Impuls-Status
unsigned long windmeterStart;
unsigned long windmeterStartAlt = 0;
int windSpeed;                      // Variable voor Wind Speed
int beaufort = 0;                   // Variable Wind in Beaufort
const int windmeterTime = 10000;
//float knoten = 0.0;
//float wind = 0.0;
unsigned int knoten;
unsigned int wind;

long oldvoltage = 0;
bool metric = true;
float lastBmpTemp;
float lastPressure;
float lastHum;
float lastTemp;
uint8_t nNoUpdatesTemp;
uint8_t nNoUpdatesHum;

int updateAll = 60;
int updateCount = 0;
uint16_t lastLux;

unsigned long SLEEP_TIME = 60000;


Adafruit_BMP085 bmp = Adafruit_BMP085();
BH1750 lightSensor;
DHT dht;

MyMessage voltage_msg(CHILD_ID_BATTERY, V_VOLTAGE);
MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
MyMessage msgLux(CHILD_ID_LIGHT, V_LIGHT_LEVEL);
MyMessage msgBtemp(CHILD_ID_BTEMP, V_TEMP);
MyMessage msgPressure(CHILD_ID_BARO, V_PRESSURE);
MyMessage msgWindSpeed(CHILD_ID_WINDSPEED, V_WIND);
MyMessage msgWGust(CHILD_ID_WINDSPEED, V_GUST);
MyMessage msgWDirection(CHILD_ID_WINDSPEED, V_DIRECTION);

void setup()
{
  analogReference(INTERNAL);
  dht.setup(DHT_DATA_PIN); // set data pin of DHT sensor
  if (UPDATE_INTERVAL <= dht.getMinimumSamplingPeriod()) 
  {
    Serial.println("Warning: UPDATE_INTERVAL is smaller than supported by the sensor!");
  }
  // Sleep for the time of the minimum sampling period to give the sensor time to power up
  // (otherwise, timeout errors might occure for the first reading)
  sleep(dht.getMinimumSamplingPeriod());
  if (!bmp.begin()) 
  {
    Serial.println("Could not find a valid BMP085 sensor, check wiring!");
    while (1) {}
  }  
  metric = getConfig().isMetric;
}

void presentation()  
{
  lightSensor.begin();
  
  sendSketchInfo("Weather Sensor", "4.1.C");
  
  present(CHILD_ID_HUM, S_HUM, "WS Humidity");
//  present(CHILD_ID_TEMP, S_TEMP, "WS Temperature");
  present(CHILD_ID_LIGHT, S_LIGHT_LEVEL, "WS Lux");
  present(CHILD_ID_BARO, S_BARO, "WS Pressure");
  present(CHILD_ID_BTEMP, S_TEMP, "WS P Temperature");
  present(CHILD_ID_WINDSPEED, S_WIND, "WS Windspeed");
  present(CHILD_ID_BATTERY, S_CUSTOM, "WS Battery"); 
}

// Wind Meter https://github.com/chiemseesurfer/arduinoWeatherstation/blob/master/weatherstation/weatherstation.ino

float windmeter()
{
  windmeterStart = millis(); // Actual start time measuringMessung
  windmeterStartAlt = windmeterStart; // Save start time
  
  windSpeedPinCounter = 0; // Set pulse counter to 0
  windSpeedPinStatusAlt = HIGH; // Set puls status High
    
  while ((windmeterStart - windmeterStartAlt) <= windmeterTime) // until 10000 ms (10 Seconds) ..
  {
    windSpeedPinStatus = digitalRead(windSpeedPin); // Read input pin 2
    if (windSpeedPinStatus != windSpeedPinStatusAlt) // When the pin status changed
    {
      if (windSpeedPinStatus == HIGH) // When status - HIGH
      {
        windSpeedPinCounter++; // Counter + 1
       }
     }
     windSpeedPinStatusAlt = windSpeedPinStatus; // Save status for next loop
     windmeterStart = millis(); // Actual time
   }
   windSpeed =  ((windSpeedPinCounter * 24) / 10) + 0.5; //  WindSpeed - one Pulse ~ 2,4 km/h, 
   windSpeed = (windSpeed / (windmeterTime / 1000)); // Devided in measure time in seconds
   Serial.print("wind Speed : ");
   Serial.println(windSpeed);    
   knoten = windSpeed / 1.852; //knot's
   return windSpeed;
}

void loop()      
{
  updateCount += 1;
  if (updateCount == updateAll) 
  {
    lastTemp = -1;
    lastHum = -1;
    lastLux = -1;
    lastBmpTemp = -1;
    lastPressure = -1;
    updateCount = 0;
   }

   long voltage = readVcc();
   if (oldvoltage != voltage) { // Only send battery information if voltage has changed, to conserve battery.
      send(voltage_msg.set(voltage / 1000.0, 3)); // redVcc returns millivolts and set wants volts and how many decimals (3 in our case)
      sendBatteryLevel(round((voltage - BATTERY_ZERO) * 100.0 / (BATTERY_FULL - BATTERY_ZERO)));
      oldvoltage = voltage;
   }
    
   delay(2000);

   // Force reading sensor, so it works also after sleep()
   dht.readSensor(true);
  
   // Get temperature from DHT library
   float temperature = dht.getTemperature();
   if (isnan(temperature)) 
   {
    Serial.println("Failed reading temperature from DHT!");
   }
   else if (temperature != lastTemp || nNoUpdatesTemp == FORCE_UPDATE_N_READS) 
   {
    // Only send temperature if it changed since the last measurement or if we didn't send an update for n times
    lastTemp = temperature;
    if (!metric) 
    {
      temperature = dht.toFahrenheit(temperature);
    }
    // Reset no updates counter
    nNoUpdatesTemp = 0;
    temperature += SENSOR_TEMP_OFFSET;
    send(msgTemp.set(temperature, 1));

    #ifdef MY_DEBUG
    Serial.print("T: ");
    Serial.println(temperature);
    #endif
    }
    else 
    {
      // Increase no update counter if the temperature stayed the same
      nNoUpdatesTemp++;
    }

    // Get humidity from DHT library
    float humidity = dht.getHumidity();
    if (isnan(humidity)) 
    {
      Serial.println("Failed reading humidity from DHT");
    } 
    else if (humidity != lastHum || nNoUpdatesHum == FORCE_UPDATE_N_READS) 
    {
      // Only send humidity if it changed since the last measurement or if we didn't send an update for n times
      lastHum = humidity;
      // Reset no updates counter
      nNoUpdatesHum = 0;
      send(msgHum.set(humidity, 1));

    #ifdef MY_DEBUG
    Serial.print("H: ");
    Serial.println(humidity);
    #endif
    }
    else 
    {
      // Increase no update counter if the humidity stayed the same
      nNoUpdatesHum++;
    }
    uint16_t lux = lightSensor.readLightLevel();
    if (lux != lastLux) 
    {
      send(msgLux.set(lux));
      lastLux = lux;
    }
    float pressure = bmp.readSealevelPressure(ALTITUDE) * 0.01;
    float bmptemp = bmp.readTemperature();
    if (!metric)
    {
      bmptemp = bmptemp * 1.8 + 32.0;
    }
    if (bmptemp != lastBmpTemp) 
    {
      send(msgBtemp.set(bmptemp,1));
      lastBmpTemp = bmptemp;
    }
    if (pressure != lastPressure) 
    {
      send(msgPressure.set(pressure, 0));
      lastPressure = pressure;
    }

    wind = windmeter();
    Serial.print("Wind : ");
    Serial.println(wind);
    int wdirection = 1;
    int wgust = 1;
    send(msgWindSpeed.set(wind, 1));
    send(msgWGust.set(wgust, 1));
    send(msgWDirection.set(wdirection, 1));
    sleep(SLEEP_TIME);
}

void incomingMessage(const MyMessage & message) 
{
  // We only expect one type of message from controller. But we better check anyway.
  if (message.isAck()) 
  {
    Serial.println("This is an ack from gateway");
  }
}

long readVcc()
{
  // From http://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/
  // Read 1.1V reference against AVcc
  // set the reference to Vcc and the measurement to the internal 1.1V reference
#if defined(__AVR_ATmega32U4__) || defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
  ADMUX = _BV(REFS0) | _BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
#elif defined (__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
  ADMUX = _BV(MUX5) | _BV(MUX0);
#elif defined (__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__)
  ADMUX = _BV(MUX3) | _BV(MUX2);
#else
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
#endif

  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Start conversion
  while (bit_is_set(ADCSRA, ADSC)); // measuring

  uint8_t low  = ADCL; // must read ADCL first - it then locks ADCH
  uint8_t high = ADCH; // unlocks both

  long result = (high << 8) | low;

  result = 1125300L / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
  return result; // Vcc in millivolts
}

It a little big but does what i need and the best thing it's that the anenometer works :+1: