Temperature controlled fan - nano- solved

Projects General Guidance
1

Looking for some guidance please.

I have a 4 wire 12v pwm fan, Arduino nano, appropriate power supplies, DHT11, 16x2lcd i2c

Everything is connected and works well except the fan, the pwm wire of the fan is connected to pin 9, grounds are all connected.

When I start everything up, the fan starts up, The speed increments seem to work ok except the fan runs slow when it should be off, display shows off

I have read others having the same problem and it's stated I have to change the PWM frequency to 25khz to get the fan to stop.

I have been reading and can't seem to get my head around how to implement and what code to add/change.

Any help would be appreciated.

#include<dht.h>      // Including library for dht
#include <Wire.h> // Library for I2C communication
#include <LiquidCrystal_I2C.h> // Library for LCD
LiquidCrystal_I2C lcd = LiquidCrystal_I2C(0x27, 16, 2); // Change to (0x27,16,2) for 16x2 LCD.


#define dht_dpin 6 
dht DHT;

#define pwm 9

byte degree[8] = 
             {
               0b00011,
               0b00011,
               0b00000,
               0b00000,
               0b00000,
               0b00000,
               0b00000,
               0b00000
             };

void setup()
{

// Initiate the LCD:
 lcd.init();
 lcd.backlight();
 
 

lcd.createChar(1, degree);

}

void loop()
{
 DHT.read11(dht_dpin);
 int temp=DHT.temperature;
 int hum=DHT.humidity;
 lcd.setCursor(0,0);
 lcd.print("Temp:");
 lcd.print(temp);   // Printing temperature on LCD
 lcd.setCursor(7,0);
 lcd.write(1);
 lcd.print("C H:");
 lcd.print(hum);
 lcd.setCursor(14,0);
 lcd.print("%");
 
 lcd.setCursor(0,1);
 if(temp <26 )
   { 
     analogWrite(pwm,0);
     lcd.print("Fan OFF            ");
     delay(100);
   }
   
   else if(temp==26)
   {
     analogWrite(pwm, 51);
     lcd.print("Fan Speed: 20%   ");
     delay(100);
   }
   
    else if(temp==27)
   {
     analogWrite(pwm, 102);
     lcd.print("Fan Speed: 40%   ");
     delay(100);
   }
   
    else if(temp==28)
   {
     analogWrite(pwm, 153);
     lcd.print("Fan Speed: 60%   ");
     delay(100);
   }
   
   else if(temp==29)
   {
     analogWrite(pwm, 204);
     lcd.print("Fan Speed: 80%    ");
     delay(100);
   }
    else if(temp>29)
   {
     analogWrite(pwm, 255);
     lcd.print("Fan Speed: 100%   ");
     delay(100);
   } 
 delay(3000);
}
2

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3

Thank you, Fixed

4

squiggy6772:
the fan runs slow when it should be off....

You are saying that when you see "Fan OFF" on the LCD, the fan is still running?

5

Just to be sure, why do you do this:

#define pwm 9

but then later you do this:

     analogWrite(9,0);
6

PaulRB:
You are saying that when you see "Fan OFF" on the LCD, the fan is still running?

Correct.

7

aarg:
Just to be sure, why do you do this:

#define pwm 9

but then later you do this:

     analogWrite(9,0);

redundant statement,
change

  analogWrite(9,0);

to

     analogWrite(pwm,0);
8

Try disconnecting the fan's speed control pin from the Arduino and connect it to 5V, then ground and then unconnected. What happens in each case?

I am unsure about the advice to use 25KHz, I don't see why that would do anything to prevent slow running when supposed to be off. The usual reason for using 25KHz is to avoid audible noise from the fan which can be caused by lower frequency pwm (25KHz being above human hearing range). After all, at 0% duty cycle, the frequency of a pwm signal is irrelevant, it doesn't have one, it's a steady 0V.

9

Solved :

From my understanding and reading that's what others did to get the fan to stop.
A Uno and other boards it's easier to control the frequency of the pwm pin..
I scrapped the idea of using a pwm fan and redid the circuit to use a TIP120 and diode to control the fan speed.

Everything works as it should.