Hi Guys
I have been working on a sketch to display temp,Humidity and dew point in F° on a lcd display. I was able to get the temperature but could not figure how to enter the formula to convert the C° to F°. I am really new to this and have just combined a couple of sketches to get to this point. I imagine that there is probably a better way to do this but like I said I am new to this Here is my sketch. Any help would be greatly appreciated !
Thanks GD
#include <Wire.h>
#include <dht11.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,20,4); // set the LCD address to 0x27 for a 20 chars and 4 line display
/*-----( Declare objects )-----*/
dht11 DHT11;
/*-----( Declare Constants, Pin Numbers )-----*/
#define DHT11PIN 2
void setup() /*----( SETUP: RUNS ONCE )----*/
{
lcd.init(); // initialize the lcd
lcd.init();
// Print a message to the LCD.
lcd.backlight();
lcd.setCursor(3,0);
Serial.begin(9600);
Serial.println("DHT11 TEST PROGRAM ");
Serial.print("LIBRARY VERSION: ");
Serial.println(DHT11LIB_VERSION);
Serial.println();
}/*--(end setup )---*/
void loop() /*----( LOOP: RUNS CONSTANTLY )----*/
{
Serial.println("\n");
int chk = DHT11.read(DHT11PIN);
Serial.print("Read sensor: ");
switch (chk)
{
case 0: Serial.println("OK"); break;
case -1: Serial.println("Checksum error"); break;
case -2: Serial.println("Time out error"); break;
default: Serial.println("Unknown error"); break;
}
Serial.print("Humidity (%): ");
Serial.println((float)DHT11.humidity, 2);
Serial.print("Temperature (F): ");
Serial.println(Fahrenheit(DHT11.temperature), 2);
Serial.print("Dew Point (F): ");
Serial.println(dewPoint(DHT11.temperature, DHT11.humidity));
Serial.print("Dew PointFast (F): ");
Serial.println(dewPointFast(DHT11.temperature, DHT11.humidity));
lcd.setCursor(3,0);
lcd.print("Gary Davis!");
lcd.setCursor(3,1);
lcd.print("Temp F:");
lcd.println(Fahrenheit(DHT11.temperature));
lcd.setCursor(1,2);
lcd.print("Humidity: ");
lcd.println((float)DHT11.humidity, 2);
lcd.setCursor(0,3);
lcd.print("Dew Point:F ");
lcd.println(dewPoint (DHT11.temperature, (DHT11.humidity*1.8 + 32)));
//lcd.println(dewPoint(DHT11.temperature, DHT11.humidity));
delay(10000);
}/* --(end main loop )-- */
/*-----( Declare User-written Functions )-----*/
//
//Celsius to Fahrenheit conversion
double Fahrenheit(double celsius)
{
return 1.8 * celsius + 32;
}
//Celsius to Kelvin conversion
double Kelvin(double celsius)
{
return celsius + 273.15;
}
// dewPoint function NOAA
// reference: http://wahiduddin.net/calc/density_algorithms.htm
double dewPoint(double celsius, double humidity)
{
double A0= 373.15/(273.15 + celsius);
double SUM = -7.90298 * (A0-1);
SUM += 5.02808 * log10(A0);
SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
SUM += log10(1013.246);
double VP = pow(10, SUM-3) * humidity;
double T = log(VP/0.61078); // temp var
return (241.88 * T) / (17.558-T);
}
// delta max = 0.6544 wrt dewPoint()
// 5x faster than dewPoint()
// reference: http://en.wikipedia.org/wiki/Dew_point
double dewPointFast(double celsius, double humidity)
{
double a = 17.271;
double b = 237.7;
double temp = (a * celsius) / (b + celsius) + log(humidity/100);
double Td = (b * temp) / (a - temp);
return Td;
}
/* ( THE END ) */
Hi GD,
Since your temperature is in celcius, just calculate the dew-point with the temp and humidty values (don't try to convert the humidity). Then just covert the dew point result to F.
Hi Tororo
I was trying to use a math formula after it had figured the dewpoint but was not having any luck. It would not come out with the right answer. I was hoping that someone would help me with a few lines for my sketch.
There are some simple examples in the first two link with using reference readings or using the Steinhart-Hart formula which would yield precise results:
Thank you very much for your help. It is very helpful for me to see the sketch and compare it to what I had done and figure out where I went wrong ! I am very new to this and I am trying to learn but my old brain is not as absorbent as it used to be I think ! hahaha