I printed out and then manually entered a sketch for reading a DHT22 temperature and humidity sensor from Electro Schematics. I am running this on a MacBook pro with OS X Captain, and my Arduino board is an Arduino Mega (though I haven’t arrived at the stage where I’ve hooked it up to my computer). After manually entering and running verify, I fixed errors in capitalization and spacing. I am now running into an error I don’t understand. It is probably a rookie mistake, but I’m having trouble understanding the problem. I’m new to Arduino ( I’ve read Make: Getting Started with Arduino, and Programing Arduino Next Steps), and new to this forum. I’ve read “how to get help with your Arduino project” and think I’ve covered the necessary bases by including my “Groundskeeper_bot” program, the downloaded library program “DHT.h” and the error message I get when I try to verify the program. I welcome any constructive criticism on the program errors and or my submission.
Thank you for your time.
// “Groundskeeper_bot” Program //
#include "DHT.h"
#define DHTPIN 2 //what pin we’re connected to
#define DHTTYPE DHT22 //DHT 22 (AM2302)
#define fan 4
int maxHum = 60;
int maxTemp = 40;
DHT dht(DHTPIN, DHTTYPE);
void setup() {
// put your setup code here, to run once:
// DHT22 sketch taken from
// electroschematics.com/11293/am2302-dht22-datasheet
pinMode(fan, OUTPUT);
Serial.begin (9600);
dht.begin();
}
void loop() {
// put your main code here, to run repeatedly:
// Wait for a few seconds between measurements
delay(2000);
//Reading temprature or humidity takes about 250 ms
//Sensor readings may also be up to 2sec. old
float h=dht.readHumidity();
//read temprature as celsius
float t=dht.readTemperature();
//check if any reads failed and exit early (to try again)
if (isnan(h) || isnan(t)) {
Serial.println("Failed to read from DHT sensor");
return;
}
if(h > maxHum || t>maxTemp) {
digitalWrite(fan, HIGH);
} else {
digitalWrite(fan, LOW);
}
Serial.print("%\t");
Serial.print("humidity: ");
Serial.print(h);
Serial.print("Temprature: ");
Serial.print(t);
Serial.println(" C ");
}
////
// DTH.h program downloaded to library and taken from internet //
////
#ifndef DHT_H
#define DHT_H
#if ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif
/* DHT library
MIT license
written by Adafruit Industries
*/
// how many timing transitions we need to keep track of. 2 * number bits + extra
#define MAXTIMINGS 85
#define DHT11 11
#define DHT22 22
#define DHT21 21
#define AM2301 21
class DHT {
private:
uint8_t data[6];
uint8_t _pin, _type, _count;
unsigned long _lastreadtime;
boolean firstreading;
public:
DHT(uint8_t pin, uint8_t type, uint8_t count=6);
void begin(void);
float readTemperature(bool S=false);
float convertCtoF(float);
float convertFtoC(float);
float computeHeatIndex(float tempFahrenheit, float percentHumidity);
float readHumidity(void);
boolean read(void);
};
#endif
////
// Error message //
////
Arduino: 1.6.7 (Mac OS X), Board: "Arduino/Genuino Uno"
/var/folders/z1/4pgxyt1n3ms73r1hkg73_0080000gn/T//ccpRQf98.ltrans0.ltrans.o: In function global constructors keyed to 65535_0_Groundskeeper_bot.ino.cpp.o.1758': ccpRQf98.ltrans0.o:(.text.startup+0x62): undefined reference to DHT::DHT(unsigned char, unsigned char, unsigned char)'
/var/folders/z1/4pgxyt1n3ms73r1hkg73_0080000gn/T//ccpRQf98.ltrans0.ltrans.o: In function main': ccpRQf98.ltrans0.o:(.text.startup+0x190): undefined reference to DHT::begin()'
ccpRQf98.ltrans0.o:(.text.startup+0x1e6): undefined reference to DHT::readHumidity()' ccpRQf98.ltrans0.o:(.text.startup+0x1f4): undefined reference to DHT::readTemperature(bool)'
collect2: error: ld returned 1 exit status
exit status 1
Error compiling.
This report would have more information with
"Show verbose output during compilation"
enabled in File > Preferences.