if + while loop DHT + humidifier

Using Arduino Programming Questions
1

hello,

I'm having a problem writing my code for a kind of box wherein I want to keep the air humidity above a certain level.

I've connected a DHT22 humidity sensor and a hacked humidifier to my arduino. If I just want to keep humidity above 70%, everything runs well. I used the following code:

if (h < 70.00)
** {**
** digitalWrite(humidifier, HIGH);**
** }**
else
** {**
** digitalWrite(humidifier, LOW);**
** }**

But now I want not just to keep the humidity-level above 70%, but I want, if humidity sinks below 70%, to keep the humidifier going until the humidity-level reaches 75%, and then start again when the level drops under 70%. I noticed otherwise the humidifier is constantly switching on and off.

To obtain this, I tried:

if (h < 70.00)
** {**
** while (h < 75.00)**
** {**
** digitalWrite(humidifier, HIGH);**
** }**
** }**

But this last piece of code doesn't work. (The display keeps showing the initial humidity-level and the humidifier keeps activated.)

I dont't understand why. Can somebody help me please?

Thanks a lot!

fagus

PS full code attached (verstuiverPin = humidifier)

slime_molds_16092015_v6.ino (1.58 KB)

2

You don't need the while. Just lose the else in the first code and make it two if statements. If humidity < 70 turn on. If humidity > 75 turn off. If the humidity is between those values, neither if will be true and the humidifier will either stay on or stay off as needed.

3

Why do you have two things ? the 'air' and the 'humidifier'. What does 'air' (luchtPin) do ?

In the loop() you have a delay of 2 seconds. Keep that, and don't use a while, just keep it running every 2 seconds.

You need to know if the humidifier is on or off. That is all you need :slight_smile:
Then you can make it turn on or off at every value.

Let's add a boolean variable called 'humidifier'.
You have to set it to true if the humidifier is turned on, and false if the humidifier is turned off.

boolean humidifer = false;   // start with the humidifier being off

void setup()
{
  ...
}

void loop()
{
  ...

  if ( h < 70.00 && !humidifer )           // less than 70% and humidifer is off ?
  {
    digitalWrite ( verstuiverPin, HIGH);   // turn it on
    humidifier = true;                           // remember that the humidifer is on
  }

  if ( h > 75.00 && humidifier )            // more than 75% and humidifier is on ?
  {
    digitalWrite ( verstuiverPin, LOW );   // turn if off
    humidifier = false;                          // remember that the humidifier is off
  }
  ...
}

[ADDED] PaulS in Reply #3 is right, the variable 'humidifier' is not needed.

4

Or, turn the humidifier on when the humidity is less than 70% and off when it is above 75%. Simple, really.

if(humidity < 70)
{
   // turn the thing on
}

if(humidity > 75)
{
   // turn it off
}
5 
    while (h < 75.00)
    {
      digitalWrite(humidifier, HIGH);
    }

That doesn't work because you aren't reading new values for h in the while loop.

I would use something like Paul suggested.

6

It works! Thanks to all!
(Ps luchtPin controls a small fan to keep the humid air from condensing)
fagus

7

Hello Im doing sorto of the same project but foud out that the humidifier only needs to go on for 3 seconds and rest 10 in order for the humidity to spread inside the container where im planning on regulating humidity and temperature.
I found that you had to do a debounde but only got to the point where i can put the humidifier on for 5 seconds and off for other 5.

Here is the code.
Im currently working in the variable withouth the DHT loaded as i figured i would advance better going from simple to complex.
Here is the code ive been using:

int inPin = 2; // the pin number for input (for me a push button)
int ledPin = 13;

int current; // Current state of the button
// (LOW is pressed b/c i'm using the pullup resistors)
int count; // How long the button was held (secs)
byte previous = HIGH;
unsigned long firstTime; // how long since the button was first pressed

void setup() {
Serial.begin(9600); // Use serial for debugging
pinMode(ledPin, OUTPUT);
digitalWrite(inPin, HIGH); // Turn on 20k pullup resistors to simplify switch input
}

void loop() {
current = digitalRead(inPin);
// if the button changes to pressed, remember the time
if (current == LOW && previous == HIGH && millis() - firstTime > 200) {
firstTime = millis();
}
// Notice that we check if the the button has been held for at least 500 ms
// This is to debounce the input (basically make sure we get the steady state of the button)
if (current == LOW && ((millis() - firstTime) % 1000) < 20 && millis() - firstTime > 50){
ledblink(1, 5000, ledPin); // Each second the button is held blink the indicator led and
count++; // and add 1 to the counter
}
// reset the counter if the button is not pressed
if (current == HIGH) {
count = 0;
}
previous = current;
}
// Just a simple helper function to blink an led in various patterns
void ledblink(int times, int lengthms, int pinnum){
for (int x=0; x<times;x++) {
digitalWrite(pinnum, HIGH);
delay (lengthms);
digitalWrite(pinnum, LOW);
delay(lengthms);
}
}