A long while back (in a galaxy very far away), we built a temp and humidity monitor with the SHT-21 chip. It’s a very accurate, albeit very expensive, solution. What if good enough, is good enough? If you don’t need scientific resolution, the DHT-11 is a very inexpensive solution. Today we built a temp and humidity monitor with this module. I started off with a DHT-11 breakout board. I used this module because it has the pull up resistor and a conditioning capacitor onboard. I connected S (signal) to pin 2, – to Gnd, and + to 5vdc.
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I downloaded the library from github and followed the tutorial from adafruit. I changed the sketch slightly, as it outputs the temperature in C, and I want to see it in F, so I changed two lines from:
Serial.print(t);
  Serial.println(” *C”);
to:
Serial.print(t*1.8+32);
  Serial.println(” *F”);
Here is the final result:
// Example testing sketch for various DHT humidity/temperature sensors
// Written by ladyada, public domain
// Fahrenheit conversion added by Steve Spence, http://arduinotronics.blogspot.com
#include “DHT.h”
#define DHTPIN 2 Â Â // what pin we’re connected to
// Uncomment whatever type you’re using!
#define DHTTYPE DHT11 Â // DHT 11
//#define DHTTYPE DHT22 Â // DHT 22 Â (AM2302)
//#define DHTTYPE DHT21 Â // DHT 21 (AM2301)
// Connect pin + (middle) of the sensor to +5V
// Connect pin SÂ Â (on the right)Â of the sensor to whatever your DHTPIN is
// Connect pin – (on the left) of the sensor to GROUND
DHT dht(DHTPIN, DHTTYPE);
void setup() {
 Serial.begin(9600);
 Serial.println(“DHTxx test!”);
 dht.begin();
}
void loop() {
 // Reading temperature or humidity takes about 250 milliseconds!
 // Sensor readings may also be up to 2 seconds ‘old’ (its a very slow sensor)
 float h = dht.readHumidity();
 float t = dht.readTemperature();
 // check if returns are valid, if they are NaN (not a number) then something went wrong!
 if (isnan(t) || isnan(h)) {
  Serial.println(“Failed to read from DHT”);
 } else {
  Serial.print(“Humidity: “);
  Serial.print(h);
  Serial.print(” %t”);
  Serial.print(“Temperature: “);
  Serial.print(t*1.8+32);
  Serial.println(” *F”);
 }
}
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