12F675 and LM35 coding issue

[Bobbo_ZA]

Hi All,

I'm a bit of a n00b when it comes to the PIC world, :-).

I have developed previously in C, Cobol, VB6 (and .net) and C++, however I have decided to use PIC Basic for my embedded projects. I started with the simple blink (with and without button input) with a few LEDs hanging off the various ports, then worked up to rotating beacons (using PWM).

My next mini learning project is to connect an LM35 to a 12F675. Along with the LM35 im connecting 3 LEDs, one white, one blue and one red simply to indicate a range of temps per color (i.e. if Temp < 30 then light the white LED etc) - Something I have got working through my Arduino and want to move to a more cost effective platform, :-).

I have spent a few evenings mulling over it and changing the code, flashing and testing with not much success. I think my issues are stemming from my lack of understanding of the various registers used i.e. ANSEL, TRISIO etc, although I think I have read the datasheet correctly its still not giving me the desired result.

Below is the code I have so far, please could you look and advise where I am going wrong?

'Using PIC 12F675 with White LED connected to Pin 7, Blue LED on Pin 6, 
'Red LED on pin 7. Vdd is supplied as a regulated 5v to pin 1, Ground to pin 8.
'LM 35 connected to Vdd and Ground + Centre pin connected to Pin 3 (AN3)
'Pin 4 disconnected - Have tried connecting to Vdd with 10K res and turning MCLR_on with no sucess 
                                               
@ device pic12F675,INTRC_OSC,wdt_off,pwrt_on,protect_off,MCLR_off
DEFINE CHAR_PACING 1000
DEFINE OSC 4                                      'Set internal osc. To 4MHz

'---------Define ADCin Parameters   
DEFINE ADC_BITS 10 'set number of bits in result
DEFINE ADC_CLOCK 3 'set clock source (3=rc)
DEFINE ADC_SAMPLEUS 50 'Set sampling time in uS

'---------Define Vairables         
samples VAR WORD        ' Multiple A/D sample accumulator
sample  VAR BYTE        ' Holds number of samples to take
temp    VAR BYTE        ' Temperature storage
           ' clear Samples

LED0	Con	0	' GPIO.0 = White LED
LED1    CON 1   ' GPIO.1 = Blue LED              
LED2    CON 2   ' GPIO.2 = Red LED   
               
'--------Configuring I/O PORTS
TRISIO = %010000   'set GPIO.0, GPIO.1, GPIO.2 as output (LEDs) & GPIO.4 as input
ANSEL = %00111000 ' Set ADC clock = Frc, GPIO.4, 1 = A/D 
ADCON0 = %10000000 ' Right justify, use Vdd as Vref 
CMCON = 7

'---------Main Program 
'Flash White LED on Start
HIGH LED0
Pause 500
LOW LED0       
              
TEMP_READ:                                      'Subroutine to measure temp
            temp = 0                            'Clear temp register
            samples = 0                         'Clear samples register 
            FOR sample = 1 TO 20                'Take 20 samples
                ADCIN 3, temp                   ' Read AN3 into temp variable
                samples = samples + temp      
                PAUSE 250                       ' Wait 1/4 seconds per reading
            NEXT sample                         
                temp = samples/20               'Average over 20 samples (Every 5 seconds)
                temp=(temp* 10)/2               
                                                 
if TEMP <20 then      'Less than 20deg - White LED
    HIGH LED0
    LOW LED1
    LOW LED2
    GOTO             TEMP_READ              
ENDIF

IF TEMP >20 AND temp <30 then       'Between 20deg and 30deg - Blue
    LOW LED0
    HIGH LED1
    LOW LED2
    GOTO             TEMP_READ              
ENDIF

IF TEMP >30 then                    'Greater than 30deg - Red
    HIGH LED2
    LOW LED1
    LOW LED0
    GOTO             TEMP_READ              
endif

END

[HenrikOlsson]

Hi,
You're not saying what the problem is, just that it doesn't do what you expect. As it looks quite alright to me I'm guessing you have problem with actually getting a reading from the ADC.

ADCON0.0 turns on/off the ADC and you have it set to '0' = OFF and I'm not sure if the ADCIN command handles that bit automatically or not. Try setting it to '1' and see what happens.

If your problem isn't related to the actual ADC then please elaborate a bit on what the problem is.

/Henrik.

[Bobbo_ZA]

Sorry, :-) you are right. Basically, its not doing anything currently. I have however checked the Data sheet and you are right, so I have changed the ADCON0 as follows: ADCON0 = %10001101, this should give me

Bit - Setting
0 - 1 = A/D Operating
1 - A/D conversion Bit (I assume ADCIN would set this to 1 when running)
2-3 - 11 = Channel 3 (AN3 / GPIO4)
4-5 - Not Used
6 - Vref, 0 = Vdd
7 - 1= Right Justify

However, even after this change and running it in the simulator (I don't have my breadboard etc here at work) it still does not even light up the <20 LED, :-(

Kind Regards
Rob

[fratello]

'Using PIC 12F675 with White LED connected to Pin 7, Blue LED on Pin 6, 
'Red LED on pin 7. Vdd is supplied as a regulated 5v to pin 1, Ground to pin 8.
'LM 35 connected to Vdd and Ground + Centre pin connected to Pin 3 (AN3)
'Pin 4 disconnected - Have tried connecting to Vdd with 10K res and turning MCLR_on with no sucess 
                                               
@ device pic12F675,INTRC_OSC,wdt_off,pwrt_on,protect_off,MCLR_off
DEFINE CHAR_PACING 1000
DEFINE OSC 4                                      'Set internal osc. To 4MHz

'---------Define ADCin Parameters   
DEFINE ADC_BITS 10 'set number of bits in result
DEFINE ADC_CLOCK 3 'set clock source (3=rc)
DEFINE ADC_SAMPLEUS 50 'Set sampling time in uS

'---------Define Vairables         
samples VAR WORD        ' Multiple A/D sample accumulator
sample  VAR BYTE        ' Holds number of samples to take
temp    VAR BYTE        ' Temperature storage
           ' clear Samples

LED0	Con	0	' GPIO.0 = White LED
LED1    CON 1   ' GPIO.1 = Blue LED              
LED2    CON 2   ' GPIO.2 = Red LED   
               
'--------Configuring I/O PORTS
TRISIO = %010000   'set GPIO.0, GPIO.1, GPIO.2 as output (LEDs) & GPIO.4 as input
ANSEL = %00111000 ' Set ADC clock = Frc, GPIO.4, 1 = A/D 
ADCON0 = %10000000 ' Right justify, use Vdd as Vref 
CMCON = 7

'---------Main Program 
'Flash White LED on Start
HIGH LED0
Pause 500
LOW LED0       
              
TEMP_READ:                                      'Subroutine to measure temp
            temp = 0                             'Clear temp register
            samples = 0                         'Clear samples register 
            FOR sample = 1 TO 20                'Take 20 samples
                ADCIN 3, temp                   ' Read AN3 into temp variable
                samples = samples + temp      
                PAUSE 250                       ' Wait 1/4 seconds per reading
            NEXT sample                         
                temp = samples/20               'Average over 20 samples (Every 5 seconds)
                temp=(temp* 10)/2               
                                                 
if TEMP <20 then      'Less than 20deg - White LED
    HIGH LED0
    LOW LED1
    LOW LED2
'    GOTO             TEMP_READ              
ENDIF

IF TEMP >20 AND temp <30 then       'Between 20deg and 30deg - Blue
    LOW LED0
    HIGH LED1
    LOW LED2
'    GOTO             TEMP_READ              
ENDIF

IF TEMP >30 then                    'Greater than 30deg - Red
    HIGH LED2
    LOW LED1
    LOW LED0
 '   GOTO             TEMP_READ              
endif

goto temp_read

END

[Charles Linquis]

It loloks to me that you are taking the 10-bit A/D samples and putting them in BYTE variable called TEMP. Changing TEMP to a word should certainly get you one more step.

[Acetronics2]

It loloks to me that you are taking the 10-bit A/D samples and putting them in BYTE variable called TEMP. Changing TEMP to a word should certainly get you one more step.

Hi, Charles

The point is interesting as the maximum ADC value WITH THIS SENSOR ... will be ~ 256, and always far from the actual use of the sensor.

so, we could use ADRESH as an open line indicator ....

Alain

[Acetronics2]

Hi, Bobbo

Your main problem was scaling temps before displaying ...

try this one :

'****************************************************************
 '*  Author  : [select VIEW...EDITOR OPTIONS]                    *
'*  Notice  : Copyright (c) 2010 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 05/03/2010                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************
'*  Name    : Temp 675'Using PIC 12F675 with White LED connected to Pin 7, Blue LED on Pin 6, 
'Red LED on pin 7. Vdd is supplied as a regulated 5v to pin 1, Ground to pin 8.
'LM 35 connected to Vdd and Ground + Centre pin connected to Pin 3 (AN3)
'Pin 4 disconnected - Have tried connecting to Vdd with 10K res and turning MCLR_on with no sucess 
                                               
@ device pic12F675,INTRC_OSC,wdt_on,pwrt_on,protect_off,MCLR_off

'DEFINE CHAR_PACING 1000
DEFINE OSC 4                                      'Set internal osc. To 4MHz

'---------Define ADCin Parameters   
DEFINE ADC_BITS 10 'set number of bits in result
DEFINE ADC_CLOCK 3 'set clock source (3=rc)
DEFINE ADC_SAMPLEUS 50 'Set sampling time in uS

ANSEL  = %00111000 ' Set ADC clock = Frc, GPIO.4, 1 = A/D 
ADCON0 = %10001100 ' Right justify, use Vdd as Vref          ' Select channel 3 !!! 
                   
CMCON = 7


'---------Define Vairables         
samples VAR WORD        ' Multiple A/D sample accumulator
dummy   var word        ' DIV32 intermediate value
sample  VAR BYTE        ' Holds number of samples to take
temp    VAR BYTE        ' Temperature storage  ... might be a WORD !!! ( 0 - 1023 !!! )

CLEAR           ' clear Variables

LED0	Con	0	' GPIO.0 = White LED
LED1    CON 1   ' GPIO.1 = Blue LED              
LED2    CON 2   ' GPIO.2 = Red LED   
               
'--------Configuring I/O PORTS
GPIO = 0
TRISIO = %010000   'set GPIO.0, GPIO.1, GPIO.2 as output (LEDs) & GPIO.4 as input

'---------Main Program 
'Flash White LED on Start

HIGH LED0
Pause 500
LOW LED0       
              
While 1

 TEMP_READ:                                      'Subroutine to measure temp   input = 10 mv/°C ~250 mv 

            temp = 0                            'Clear temp register
            samples = 0                         'Clear samples register
             
            FOR sample = 1 TO 20                'Take 20 samples
                ADCIN 3, temp                   ' Read AN3 into temp variable    result is ~ 50  ( .25 / 5 * 1024 )
                samples = samples + temp      
                PAUSE 12                       ' Wait 1/4 seconds per display ... (20 x 12 ms )
            NEXT sample
                                     
                temp = samples/20               'Average over 20 samples (Every 5 seconds)   result is ~ 50
'                temp=(temp* 10)/2               ' Result is 250 ... may overflow !!! so, the mult is no use !!!

'*******************************************************************************
' Trim to scale
'********************************************************************************

  Dummy = 500 * temp                            ' 500 = 5000 mv full scale  / 10 mv per degree
  temp = DIV32 1024                               ' Number is Deg C Now ...

'********************************************************************************

 SELECT CASE temp

    CASE is < 20    'Less than 20deg - White LED                                             
  
    HIGH LED0
    LOW LED1
    LOW LED2
 

    CASE is < 31        'Between 20deg and 30deg - Blue
    
    LOW LED0
    HIGH LED1
    LOW LED2
  

    CASE is < 45         'Greater than 30deg - but less than 45 deg Red
    
    HIGH LED2
    LOW LED1
    LOW LED0
    
    CASE Else              ' Too cold !!! or dangerously hot ... let's blink everyting !!!
    
    HIGH LED0
    HIGH LED1
    HIGH LED2
    
    PAUSE 250
    
    LOW LED0
    LOW LED1
    LOW LED2
    
 END SELECT
 
wend

END

Interesting parts have been explained ...

now, have a good bath ... you've sweat a lot on this one ... ROFL.