Interfacing LM35 with MSP430 Launch pad

Have you checked that you are actually getting an appropriately-varying signal at the correct MSP430 input pin...?

Andy Neil said:

Have you checked that you are actually getting an appropriately-varying signal at the correct MSP430 input pin...?

 

Yes i have checked, Its varying......

Karthik R said:

Yes i have checked, Its varying......

First you are doing inefficient timer delay for Ref to settle. Simple delay_cycles at default DCO freq can do the job.

What's that:

 IntDegF = (temp/6.82)+33.8;

http://en.wikipedia.org/wiki/Integer_(computer_science)

hi, this is code regarding delay for Ref to settle,  Can u pls suggest what change has to be made so that code will exe without any problem, Pls help me as i'm new to MCu, 

__enable_interrupt(); // Enable interrupts.
TACCR0 = 30; // Delay to allow Ref to settle
TACCTL0 |= CCIE; // Compare-mode interrupt.
TACTL = TASSEL_2 | MC_1; // TACLK = SMCLK, Up mode.
LPM0; // Wait for delay.
TACCTL0 &= ~CCIE; // Disable timer Interrupt
__disable_interrupt();

Karthik R said:

so that code will exe without any problem

I did not say that your timer-based delay have problem. Perhaps it works. Such delay is just waste of timer peripheral and code memory. As I said - use __delay_cycles(Ncycles); function to do delay here.

Clearly your code have other problems like:

    IntDegF = (temp/6.82)+33.8;
    IntDegC=(temp/6.82);

Those lines actually are translated into:

    IntDegF = (temp/6)+33;
    IntDegC=(temp/6);

You can't do floating point math with integer variables!

If your code does not work - try examples, see how they do the job, compare to your code, check differences. Debug your code step by step to see that you are getting ADC values you expect, that your math is giving results you expect and so on.

This is highly unproductive to ask others in the internet to check your code instead of debugging it to see what's actually happening in your uC :D

Ilmars said:

I did not say that your timer-based delay have problem. Perhaps it works. Such delay is just waste of timer peripheral and code memory.

Ilmars said:

Clearly your code have other problems like:

    IntDegF = (temp/6.82)+33.8;
    IntDegC=(temp/6.82);

Those lines actually are translated into:

    IntDegF = (temp/6)+33;
    IntDegC=(temp/6);

You can't do floating point math with integer variables!

Well, you're wrong even if you're right.

First, of course you can do floating point math with integer values (if not, the compiler would throw an error). Whether it gives you the expected result, is a different story.
The compiler will cast the innteger part to float and then perform the operation, then truncate the result back to integer.

AFAIK

    IntDegF = (temp/6.82)+33.8;

translates to

   intDegF = (long) (((float)temp / 6.82)+33.8).

as the compiler promotes to the larger type of the two operands.

See here for a nice summary. With citations from the C standard (I know, citing standards is uncommon for me, I usually leave this to others, but this time I wanted to know.)

Karthik R said:

I have got held up with this code for very long time and the temperature is not changing according to the change in the environment

Karthik R said:

while(1)[...]
  ADC10CTL0&= ~ENC;

    while(1)

          {

           

           }

    __no_operation();                       // SET BREAKPOINT HERE

  }

Jens-Michael Gross said:

I have got held up with this code for very long time and the temperature is not changing according to the change in the environment

Karthik R said:

while(1)[...]
  ADC10CTL0&= ~ENC;

    while(1)

          {

           

           }

    __no_operation();                       // SET BREAKPOINT HERE

  }

Well,the temperature might change, but your only measure it once, then your code gets caught in this inner while(1) loop and never does a second measurement.

[/quote]

I'm really  sorry for the late reply as i was travelling, can u pls tell , what change has to be made in the code so that i will get continuous reading and display the same, as i'm new to prog language Pls help me in this

thank you.  

Thank you Jens-Michael Gross, for your reply , as u spotted the problem is in the while loop, i removed the loop and the code runs well and it does give the change in temperature according to environment , but i have a small prob , the temp value is not getting stabilized , Pls help me out in this

thank you

Jens-Michael Gross said:

translates to

   intDegF = (long) (((float)temp / 6.82)+33.8).

Ups. You are so right :) Thing is that I would never in my life write such kind of [...] type conversion for 16bit uC, especially to convert ADC'ed temperature to integer. So my mind played funny trick here :)

Jens-Michael Gross said:

but this time I wanted to know

LOL. Me either. I suggest this in return.

Ilmars said:

translates to

   intDegF = (long) (((float)temp / 6.82)+33.8).