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Topic: Trouble with DHT22. (Read 161 times) previous topic - next topic


I am trying to use the information from the dht22 sensor to control other pins, and can't seem to get it to work. I have an Arduino Uno attached to a relay board and am trying to get it to switch on circuits when the temp/humidity drops below a certain level. As of right now both circuits stay on no matter what. Here is my code, and any help is appreciated.

Code: [Select]

int heat = 4; // set heat circuit to pin 4
int humid = 8; // set humidity circuit to pin 8

#include "DHT.h"

#define DHTPIN 2     // what pin we're connected to

// Uncomment whatever type you're using!
#define DHTTYPE DHT22   // DHT 22  (AM2302)

// Connect pin 1 (on the left) of the sensor to +5V
// NOTE: If using a board with 3.3V logic like an Arduino Due connect pin 1
// to 3.3V instead of 5V!
// Connect pin 2 of the sensor to whatever your DHTPIN is
// Connect pin 4 (on the right) of the sensor to GROUND
// Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor

// Initialize DHT sensor for normal 16mhz Arduino
// NOTE: For working with a faster chip, like an Arduino Due or Teensy, you
// might need to increase the threshold for cycle counts considered a 1 or 0.
// You can do this by passing a 3rd parameter for this threshold.  It's a bit
// of fiddling to find the right value, but in general the faster the CPU the
// higher the value.  The default for a 16mhz AVR is a value of 6.  For an
// Arduino Due that runs at 84mhz a value of 30 works.
// Example to initialize DHT sensor for Arduino Due:

void setup() {
  pinMode (heat , OUTPUT);
  pinMode (humid , OUTPUT);
  Serial.println("DHTxx test!");

void loop() {
  // Wait a few seconds between measurements.
  // 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();
  // Read temperature as Celsius
  float t = dht.readTemperature();
  // Read temperature as Fahrenheit
  float f = dht.readTemperature(true);

  // Check if any reads failed and exit early (to try again).
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println("Failed to read from DHT sensor!");

  // Compute heat index
  // Must send in temp in Fahrenheit!
  float hi = dht.computeHeatIndex(f, h);

if ('Humidity' <= 90) // declare function if humidity drops below 90%
  digitalWrite , humid , HIGH ; // Turn humidity circuit on
  digitalWrite , humid , LOW; //if humidity is above 90% keep circuit off

if ('Temperature' <= 25)// declare function if temp drops below 25 Celsius
  digitalWrite , heat , HIGH; //turn heat circuit on
  digitalWrite , heat , LOW; // if heat is above 25 Celsius keep heat circuit off

  Serial.print("Humidity: "); //send info to monitor to visually verify data
  Serial.print(" %\t");
  Serial.print("Temperature: ");
  Serial.print(" *C ");
  Serial.print(" *F\t");
  Serial.print("Heat index: ");
  Serial.println(" *F");




if ('Humidity' <= 90) // declare function if humidity drops below 90%

Here you compare a character constant and a numeric constant, what will yield always a constant result - in ASCII either TRUE since 'H'<90, or FALSE since 'Hu'>90. You want something like

if (h <= 90) // declare function if humidity drops below 90%

to compare the actual humidity, supposedly stored in the variable h, against a constant threshold value.


Thank you. I changed the characters accordingly and still seem to have the same problem though.


please try

digitalWrite , humid , HIGH ; // Turn humidity circuit on


digitalWrite(humid , HIGH) ; // Turn humidity circuit on
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)


Working perfectly now!! Thank you both so much for your help! I'm really looking forward to doing this project now.

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