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Need help.

e14 Contributor

Hi all.

I need your help. I am building a thermostat that has a fan. The fan starts working when the temprature is too high as well as a red led lights. The problem is that when the red led lights the temprature increases a lot. Why that happens?

  • 0

    It would help if we could see a schematic to see how you are driving the LED.  Do you have a current-limiting resistor in series with the LED?  If you don't, the transistor driving the LED can get very hot and may fail.  If the transistor is inside a microcontroller, that microcontroller will get hot and may fail.

     

    Typical current-limiting resistor value is 200-1000 Ohms, depending on how bright you want your LED.

  • 0 in reply to johnbeetem

      It may be difficult for you to undrestand. By the way I am new in Arduino and the deadline is near so I am in hurry image

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  • 0 in reply to e14 Contributor

    in addition to Johns comments

     

    The following devices should not be driven directly by the Arduino

     

    Speaker

    Motor

    LEDs without suitable current limiting resistors as John stated but if you want it to be bright then use one of the channels of the LM2003 as stated below

     

    to drive the speaker and the motor you need to employ a transistor driver or another chip to help like an LM2003 which is an 8 channel driver capable of driving the motor and the speaker easily. Speaker may still need a limiting resistor if it a low impedance one (8 - 16 ohms is a lot of current)

     

    a schematic would help too as I can not determine what is connected to what with your picture, only what some of the components are. Also please post the code your testing

     

    what is the model temp sensor

     

    with the direct load you are putting on the controller I am surprised anything is working and if it is it may not for very long.

     

    Show me your schematic and code and I will correct the errors for you that I find

     

    Peter

  • 0

    Hi Selim,

    What is getting hotter? The LED? The CPU? or the temperature sensor?

    As the others mentioned some of the components can get hot if they have too much current passing through, so the driver circuitry may need to be improved, but if it is just the sensor that is showing an increase in temperature, is the fan blowing hotter air onto the sensor - indicating the sensor is not normally exposed to the hottest temperature?

  • 0 in reply to Robert Peter Oakes

    Peter Oakes wrote:

     

    The following devices should not be driven directly by the Arduino

     

    Speaker

    Motor

    LEDs without suitable current limiting resistors as John stated but if you want it to be bright then use one of the channels of the LM2003 as stated below

     

    to drive the speaker and the motor you need to employ a transistor driver or another chip to help like an LM2003 which is an 8 channel driver capable of driving the motor and the speaker easily. Speaker may still need a limiting resistor if it a low impedance one (8 - 16 ohms is a lot of current)

    Adding to Peter's suggestions, when you drive an inductive load like a motor, speaker, or electro-mechanical relay be sure you include a flyback diode.  They are built into the LM2003 (I think) and most motor drivers, but if you use discrete transistors you'll need to add your own.  If you don't, the driver transistor is likely to get fried.  Here's the Wikipedia page: http://en.wikipedia.org/wiki/Flyback_diode

  • 0 in reply to johnbeetem

    John

     

    You are correct, they are indeed included in the 2003 and those devices are capable of over 500mA per channel, more than enough for this application

  • 0

    hi all, thanks for your replying. this is what i have done. I also need to connect a fan when the temprature is very high.

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  • 0

    //this is the code that I wrote

    //include the LCD library and initialize

    #include <LiquidCrystal.h>

    LiquidCrystal lcd(2, 3, 4, 5, 6, 7);

     

     

    //pin connections

    const int redLed = 13;

    const int yellowLed= 12;

    const int greenLed = 11;

    const int speaker = 10;

    const int fan = 9;

     

     

    const int tempraturePin = A1;

     

     

        int freq = 440;

        int duration = 1000;

      //  tone(pinOut, freq, duration);

    //tempratures 

    int temprature=0;

    const int minTemprature = 30;

    const int midTemprature = 35;

    const int maxTemprature = 40;

     

     

    void setup() {

      pinMode(fan, OUTPUT);

      pinMode(speaker, OUTPUT);

      pinMode(redLed, OUTPUT);

      pinMode(yellowLed, OUTPUT);

      pinMode(greenLed, OUTPUT);

      pinMode(tempraturePin, INPUT);

      lcd.begin(16, 2);                  //the size of the LCD

    }

     

     

    void loop() {

     

     

      temprature = readTemprature();

     

      if(temprature > minTemprature){

        digitalWrite(greenLed, HIGH);

        digitalWrite(redLed, LOW);

        digitalWrite(yellowLed, LOW);

       

        lcd.setCursor(12,1);         

        lcd.print("ON");

      }

    else if(temprature > midTemprature){

        digitalWrite(yellowLed, HIGH);

        digitalWrite(greenLed, LOW);

        digitalWrite(redLed, LOW);

       

        lcd.setCursor(12,1);         

        lcd.print("ON");

      }

      else if (temprature > maxTemprature){

        digitalWrite(redLed, HIGH);

        digitalWrite(yellowLed, LOW);

        digitalWrite(greenLed, LOW);

        digitalWrite(fan, HIGH);

        tone(speaker, freq, duration);

     

     

        lcd.setCursor(12,1);         

        lcd.print("ON");

      }

     

      else{

        lcd.setCursor(12,1);         

        lcd.print("OFF");

      }

      

       //print a static message to the LCD

       lcd.setCursor(0,0);         //move the cursor to the beginning of the LCD

       lcd.print("Temprature:");   //prints the word Temprature:

       lcd.setCursor(12,0);        //move cursor to 12

       lcd.print(temprature);      //display the temperature

       lcd.setCursor(14,0);        //move cursor to 15

       lcd.print((char)223);       //prints the degree character

       lcd.print("C");             //prints the word C

       

       lcd.setCursor(0,1);         //move cursor to second line

       lcd.print("Fan is:");       //prints the words Fan is:

      

       delay(1000);

       lcd.clear();  

    }

    // get the temperature and convert it to celsius

       int readTemprature() { 

         temprature = analogRead(tempraturePin);

         return temprature * 0.48828125;

    }

  • 0 in reply to e14 Contributor

    you need resistors in series with the LEDs and should invert the drive by having the Arduino sink the low side of the LED to ground, use a 220+ ohm resistor.

     

    the LM35 circuit leave a bit to be desired, look to page 11 in the TI data sheet http://www.ti.com/lit/gpn/lm35. at room temperature your only getting maybe 200-250mV out of the device, this is very low relative to the capability of the ADC in the Arduino and the default ADC range is 0 - 5000mV (5V) so only 5mV per step equating to 1/2deg C. If you change the reference voltage of the ADC to use the 1.1V band gap internal reference you will improve the measurement capability considerably (1mV per step). An alternate approach would be to use a digital temp sensor or put an OP Amp between the sensor and the Arduino.

     

    if your speaker and motor (Not shown in the schematic) are also being connected to the Arduino and being driven directly you will at a minimum have noise on the supply and it will also drop the supply value by some amount and this will affect the ADC measurement as it is also used as the reference for the ADC the affect being that the temp will rise significantly as your basing your reading on the 5V as a reference.

     

    mathematically

     

    5V\1024 = 4.88mV per step

    20degC @ 10mV per deg = 200mV

    reading would be 200\4.88mV = 40 - 41 on the ADC

    * .48828125 = 20.00 deg... works great

     

    now assume the volts dropped to 4.5V instead

    4.5\1024 = 4.39mV per step

    reading 200mV/4.39mV = 45.55

    *4.8828125 = 22.24 so an increase of 10%, this would be 25deg (+20%) if the volts went down to 4v, noise on the supply from motot and speaker could make this even worse.

     

    to fix this and improve the stability set the ADC to use the band gap or use a separate PSU for all the loads (And decouple the output of the LM35 as shown on page 11 of data sheet)

     

    either way you should not drive the speaker and motor/Fan directly from the Arduino, it will cause you problems.

     

    One last thing, breadboards are notorious for creating noise if your not careful (All those connections), a 10uF +.1uF cap or something on the supply close to the LM35 will help eliminate noise but wont prevent the supply drop effect.

     

    I hope I have provided a little insight into accurate measurements and highlighted a few pitfalls to watch out for.

     

    Peter

     

     

    if i'm right, please click correct answer image

  • 0

    you are correct. Is it possible for you to send me a schematic so I can easily understand how to connect them? By the way do I need to use the motor or not?