Temperature with the LM34C

Closed Thread
Results 1 to 26 of 26

Hybrid View

  1. - 26th January 2009, 23:34 #1
    mister_e's Avatar
    mister_e
    mister_e is offline Contributor
    Join Date
    Sep 2004
    Location
    montreal, canada
    Posts
    6,898

    Did you find this post helpful? Yes | No

    Default

    Look in your PIC datasheet in the analog to digital converter section. There you will find the maximum impedance you may use with your Specific PIC model.

    Usually a simple small trim-pot (single or multi-turn) work pretty well... You could also use a already made voltage reference, this doesnt require any calibration and tend to be more stable on the long run.
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.
  2. - 28th May 2009, 20:39 #2
    StoneColdFuzzy's Avatar
    StoneColdFuzzy
    StoneColdFuzzy is offline Junior Member
    Join Date
    Jan 2009
    Posts
    36

    Did you find this post helpful? Yes | No

    Default

    OK, I'm using a PIC16F877a instead of the PIC16F877. I have a 4 MHz ceramic osc and I'm using the direct connection as on the Rentron page. I don't know if I need to do this or not, but I have the VSS and VDD pins tied together, respectively. I checked the connections and tested the LM34 with 5 volts. The LM34 changes output voltage fine I don't know if I goofed the code up or not, but I'm getting nothing. Here's the code:

    Code:
    @ device  pic16F877A, xt_osc, wdt_off, lvp_off, protect_off

DEFINE loader_used 1    ' Boot loader is being used
DEFINE debug_mode  1    ' Debug sending Inverted serial data
DEFINE debug_reg portc  ' Debug Port = PortC
DEFINE debug_bit 6      ' Debug.bit = PortC.6
DEFINE debug_baud 9600  ' Default baud rate = 9600
DEFINE osc 4            ' We're using a 4 MHz oscillator
DEFINE ADC_BITS 8       ' Set A/D for 8-bit operation
DEFINE ADC_CLOCK 1      ' Set A/D clock Fosc/8
DEFINE ADC_SAMPLEUS 50  ' Set A/D sampling time @ 50 uS
samples VAR WORD        ' Multiple A/D sample accumulator
sample  VAR BYTE        ' Holds number of samples to take
temp    VAR BYTE        ' Temperature storage
samples = 0             ' Clear samples accumulator on power-up

    TRISA = %11111111   ' Set PORTA to all input
    ADCON1 = %00000011  ' Set PORTA.0,1,2,5 = A/D, PortA.3 = +Vref
    PAUSE 500           ' Wait .5 second

loop:
    FOR sample = 1 TO 20    ' Take 20 samples
        ADCIN 0, temp       ' Read channel 0 into temp variable
        samples = samples + temp ' Accumulate 20 samples
        PAUSE 250           ' Wait approximately 1/4 seconds per loop
    NEXT sample
    temp = samples/20
    DEBUG "Temperature is: ",DEC temp," Deg F",10,13
    samples = 0             ' Clear old sample accumulator
    GOTO loop               ' Do it forever

    END
  3. - 28th May 2009, 21:47 #3
    mackrackit's Avatar
    mackrackit
    mackrackit is offline SuperMod
    Join Date
    Nov 2003
    Location
    Wellton, U.S.A.
    Posts
    5,924

    Did you find this post helpful? Yes | No

    Default

    What do you have connected to AN3? If nothing then try
    ADCON1 = %00000100
    Dave
    Always wear safety glasses while programming.
  4. - 28th May 2009, 21:57 #4
    StoneColdFuzzy's Avatar
    StoneColdFuzzy
    StoneColdFuzzy is offline Junior Member
    Join Date
    Jan 2009
    Posts
    36

    Did you find this post helpful? Yes | No

    Default

    Quote Originally Posted by mackrackit View Post
    What do you have connected to AN3? If nothing then try
    ADCON1 = %00000100
    I have the wiper of a pot connected and set at 2.55 volts.

    ~ Dave
  5. - 29th May 2009, 01:04 #5
    aratti's Avatar
    aratti
    aratti is offline Senior Member
    Join Date
    May 2008
    Location
    Italy
    Posts
    825

    Did you find this post helpful? Yes | No

    Default

    I don't know if I need to do this or not, but I have the VSS and VDD pins tied together, respectively.
    Dave, Vss is the ground or (zero volts) and Vdd is power or (+5Volts), from what you say it seems you have a short.

    Remove it and re-establish the corrected connections.

    Al.
    All progress began with an idea
  6. - 29th May 2009, 01:07 #6
    StoneColdFuzzy's Avatar
    StoneColdFuzzy
    StoneColdFuzzy is offline Junior Member
    Join Date
    Jan 2009
    Posts
    36

    Did you find this post helpful? Yes | No

    Default

    There is no short. There are two VVS pins and two VDD pins. They are tied together respectively. In other words, the VVS pins are tied to each other; the VDD pins are also tied to each other.

    ~ Dave
    Last edited by StoneColdFuzzy; - 29th May 2009 at 01:09.
  7. - 29th May 2009, 08:04 #7
    mackrackit's Avatar
    mackrackit
    mackrackit is offline SuperMod
    Join Date
    Nov 2003
    Location
    Wellton, U.S.A.
    Posts
    5,924

    Did you find this post helpful? Yes | No

    Default

    I had to set this up myself to find the problem.

    When you use "DEFINE" everything has to be upper case. It would not work until I made that change. Problem was so simple but hard to see.
    Code:
    <html>
<body><!--StartFragment--><pre><code><font color="#000000">    <font color="#FF0000">DEFINE </font><font color="#0000FF">OSC </font>20
    @ <font color="#0000FF"><b>__config _HS_OSC </b></font>&amp; <font color="#0000FF"><b>_WDT_ON </b></font>&amp; <font color="#0000FF"><b>_LVP_OFF </b></font>&amp; <font color="#0000FF"><b>_CP_OFF
    </b></font><font color="#000080"><i>'DEFINE loader_used 1    ' Boot loader is being used
    </i></font><font color="#FF0000"><b>DEFINE </b></font><font color="#0000FF"><b>DEBUG_MODE  </b></font>1    <font color="#000080"><i>' Debug sending INVERTED serial data
    </i></font><font color="#FF0000"><b>DEFINE </b></font><font color="#0000FF"><b>DEBUG_REG PORTC  </b></font><font color="#000080"><i>' Debug Port = PortC
    </i></font><font color="#FF0000"><b>DEFINE </b></font><font color="#0000FF"><b>DEBUG_BIT </b></font>6      <font color="#000080"><i>' Debug.bit = PortC.6
    </i></font><font color="#FF0000"><b>DEFINE </b></font><font color="#0000FF"><b>DEBUG_BAUD </b></font>9600  <font color="#000080"><i>' Default baud rate = 9600
    </i></font><font color="#FF0000"><b>DEFINE </b></font><font color="#0000FF"><b>ADC_BITS </b></font>8       <font color="#000080"><i>' Set A/D for 8-bit operation
    </i></font><font color="#FF0000"><b>DEFINE </b></font><font color="#0000FF"><b>ADC_CLOCK </b></font>1      <font color="#000080"><i>' Set A/D clock Fosc/8
    </i></font><font color="#FF0000"><b>DEFINE </b></font><font color="#0000FF"><b>ADC_SAMPLEUS </b></font>50  <font color="#000080"><i>' Set A/D sampling time @ 50 uS
    </i></font><font color="#0000FF"><b>samples </b></font><font color="#FF0000"><b>VAR WORD        </b></font><font color="#000080"><i>' Multiple A/D sample accumulator
    </i></font><font color="#0000FF"><b>sample  </b></font><font color="#FF0000"><b>VAR BYTE        </b></font><font color="#000080"><i>' Holds number of samples to take
    </i></font><font color="#0000FF"><b>temp    </b></font><font color="#FF0000"><b>VAR BYTE        </b></font><font color="#000080"><i>' Temperature storage
    </i></font><font color="#0000FF"><b>samples </b></font>= 0             <font color="#000080"><i>' Clear samples accumulator on power-up

    </i></font><font color="#0000FF"><b>TRISA </b></font>= %11111111   <font color="#000080"><i>' Set PORTA to all input
    </i></font><font color="#0000FF"><b>ADCON1 </b></font>= %00000011  <font color="#000080"><i>' Set PORTA.0,1,2,5 = A/D, PortA.3 = +Vref
    </i></font><font color="#FF0000"><b>PAUSE </b></font>500           <font color="#000080"><i>' Wait .5 second

    </i></font><font color="#0000FF"><b>loop</b></font>:
    <font color="#FF0000"><b>FOR </b></font><font color="#0000FF"><b>sample </b></font>= 1 <font color="#FF0000"><b>TO </b></font>20    <font color="#000080"><i>' Take 20 samples
        </i></font><font color="#FF0000"><b>ADCIN </b></font>0, <font color="#0000FF"><b>temp       </b></font><font color="#000080"><i>' Read channel 0 into temp variable
        </i></font><font color="#0000FF"><b>samples </b></font>= <font color="#0000FF"><b>samples </b></font>+ <font color="#0000FF"><b>temp </b></font><font color="#000080"><i>' Accumulate 20 samples
        </i></font><font color="#FF0000"><b>PAUSE </b></font>250           <font color="#000080"><i>' Wait approximately 1/4 seconds per loop
    </i></font><font color="#FF0000"><b>NEXT </b></font><font color="#0000FF"><b>sample
    temp </b></font>= <font color="#0000FF"><b>samples</b></font>/20
    <font color="#FF0000"><b>DEBUG </b></font><font color="#00FF00"><b><i>&quot;Temperature is: &quot;</i></b></font>,<font color="#FF0000"><b>DEC </b></font><font color="#0000FF"><b>temp</b></font>,<font color="#00FF00"><b><i>&quot; Deg F&quot;</i></b></font>,10,13
    <font color="#0000FF"><b>samples </b></font>= 0             <font color="#000080"><i>' Clear old sample accumulator
    </i></font><font color="#FF0000"><b>GOTO </b></font><font color="#0000FF"><b>loop               </b></font><font color="#000080"><i>' Do it forever
    </i></font><font color="#FF0000"><b>END
</b></font></code></pre><!--EndFragment--></body>
</html>
    Last edited by mackrackit; - 29th May 2009 at 08:11.
    Dave
    Always wear safety glasses while programming.
« Previous Thread | Next Thread »

Similar Threads

  1. An algorithm for controlling temperature and humidity of greenhouse and aviculture
    By amindzo in forum mel PIC BASIC Pro
    Replies: 10
    Last Post: - 17th February 2012, 08:19
  2. DS18S20 reading negative temperature
    By srob in forum mel PIC BASIC Pro
    Replies: 6
    Last Post: - 28th December 2007, 22:21
  3. Conversion problem
    By eva in forum mel PIC BASIC Pro
    Replies: 4
    Last Post: - 15th March 2007, 19:21
  4. Help for decimal conversion
    By eva in forum mel PIC BASIC Pro
    Replies: 2
    Last Post: - 15th March 2007, 19:20
  5. Interrupt and Serial communication to PC.
    By obaskirt in forum mel PIC BASIC
    Replies: 2
    Last Post: - 17th June 2005, 21:01

Members who have read this thread : 0

You do not have permission to view the list of names.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts

Forum Rules