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Software => Software => Topic started by: galannthegreat on September 22, 2010, 09:21:41 PM

Title: Temperature Sensor Arduino Program with LM335
Post by: galannthegreat on September 22, 2010, 09:21:41 PM

I am currently working on a data logging project right now with an Arduino and I have some code working, but I want to make it a bit more accurate. I am wondering if people know of any ways I can do that.

Here is my code:

Code: [Select]

#define SENSOR 0 // select the input pin for
                 // the LM335A temperature sensor

float val = 0; // variable used to store the value
               // coming from the sensor
float val2 = 0;
float celcius = 0;

void setup()
{
  Serial.begin(9600); // open the serial port to send
                      // data back to the computer at
                      // 9600 baud
}

void loop()
{
  val = analogRead(SENSOR); // read value from the sensor
  val2 = val/2;
  celcius = val2 - 274;
 
  Serial.println(celcius); // print the value to
                           // the serial port
                       
  delay(1000); // wait 1 second between each
               // each reading
}

Thanks, Kurt.

Title: Re: Temperature Sensor Arduino Program with LM335
Post by: rbtying on September 22, 2010, 10:35:01 PM

What sensor are you using?  Also, what do you want to make a bit more accurate?  Please clarify

Sorry, I didn't read the title.

The LM335 has an output of 1mv/K

Your code uses analogRead, which uses a 10-bit ADC to convert the 0-5v into 0-1024 bits.

As such, you need to start by converting the reading back into volts:

Code: [Select]

val *= 0.0048828125;
Then, divide the voltage by 100 to get 10mV resolution.  At this point, you should cast to a shorter variable to avoid floating-point operations

Code: [Select]

int deg = val / 100;
Lastly, subtract 273.15 degrees to get degrees Celcius from Kelvin:

Code: [Select]

deg -= 273;
In summary:

Code: [Select]

deg = (int)(analogRead(SENSOR)*0.0048828125/100)-273;
Make sense?

Title: Re: Temperature Sensor Arduino Program with LM335
Post by: galannthegreat on September 23, 2010, 12:12:24 AM

Thank you very much for that :), it helped me figure out what I wanted to do.

Here is the new code: (I didn't follow exactly what you did but I did the same sort of thing)

Code: [Select]

#define SENSOR 0 // select the input pin for
                 // the LM335A temperature sensor

float val = 0; // variable used to store the value
               // coming from the sensor
float val2 = 0;
float deg = 0;
float celcius = 0;

void setup()
{
  Serial.begin(9600); // open the serial port to send
                      // data back to the computer at
                      // 9600 baud
}

void loop()
{
  val = analogRead(SENSOR); // read value from the sensor
  val2 = val * 0.00489; // take SENSOR value and multiply it by 4.89mV
                        // and store value to val2
  deg = val2 * 100; // multiply by 100 to get degrees in K
  celcius = deg - 273.15; // subtract absolute zero to get degrees celcius
   
  Serial.println(celcius); // print the value to
                           // the serial port
                       
  delay(1000); // wait 1 second between each
               // each reading
}

P.S. It also turns out that I should precisely calibrate the sensor to get more accurate results, but it is doing what I want. YAY!