LM35DZ and 18F2455 settings

[ronjodu]

I use two LM34s with a 16f876 and it's been rock solid with the following snippetts....

DEFINE LOADER_USED	1
DEFINE OSC 4
DEFINE ADC_BITS 8             ' Set A/D for 8-bit operation
DEFINE ADC_CLOCK 3            ' Set A/D clock 
DEFINE ADC_SAMPLEUS 50        ' Set A/D sampling time @ 50 uS

        '((((((((((((((((((((((((((((((((((((((()))))))))))))))))))))))))))))))))))))))
                           'Subroutine to get room temperature
        '((((((((((((((((((((((((((((((((((((((()))))))))))))))))))))))))))))))))))))))


roomdegrees:
    
    FOR sample = 1 TO 20    ' Take 20 samples
        ADCIN 2, roomtemp       ' Read channel 2 into temp variable
        samples = samples + roomtemp ' Accumulate 20 samples
    NEXT sample
        roomtemp = samples/20
        samples = 0             ' Clear old sample accumulator
    SerOut2 PORTC.6,SPbaud, [$00, $80, $29,roomtemp] 'update siteplayer with room temperature
    if r7sched = 0 then return                 'manual control = 0, auto control = 1
    if roomtemp >= roomspt + 1 then
    SerOut2 PORTC.6,SPbaud, [$00, $80, $3C,1] 'update siteplayer with exhaust status on
    checkrelays = 1
    endif
    if roomtemp <= roomspt - 1 then
    SerOut2 PORTC.6,SPbaud, [$00, $80, $3C,0] 'update siteplayer with exhaust status off
    checkrelays = 1
    endif
    return
        '((((((((((((((((((((((((((((((((((((((()))))))))))))))))))))))))))))))))))))))
                           'Subroutine to get tank temperature
        '((((((((((((((((((((((((((((((((((((((()))))))))))))))))))))))))))))))))))))))

tankdegrees:
    
    FOR sample = 1 TO 20    ' Take 5 samples
        ADCIN 4, watertemp       ' Read channel 4 into watertemp variable
        samples = samples + watertemp ' add 5 samples
    NEXT sample
        watertemp = samples/20
        samples = 0             ' Clear old samples
    SerOut2 PORTC.6,SPbaud, [$00, $80, $28,watertemp] 'update siteplayer with water temperature
    if r8sched = 0 then return                        'manual control = 0, auto control = 1
    if watertemp > waterspt then
    serOut2 PORTC.6,SPbaud, [$00, $80, $3D,0] 'update siteplayer with heater status off
    checkrelays = 1
    endif
    if watertemp <= waterspt - 1 then
    SerOut2 PORTC.6,SPbaud, [$00, $80, $3D,1] 'update siteplayer with heater status on
    checkrelays = 1
    endif
    return

I know you're using a different micro but maybe this will help some.

[Mark J]

Thanks ronjodu,
Do you have it display with fractional degrees c? ie 25.4C or just straight values ie 25.
Also noticed that the pic chip your using and also the one on the link I have in my post both use 8 bit ADC_BITS, wheras the 18F's use 10, so not sure if that might have something to do with it also as it could be because im basing the reading/loop/convertion on an 8 bit value.

[Mark J]

Just done a couple of tests.

Set the Vref back to AN3 and just simply did ADCIN 0,VAL and then print it out to the LCD with a DEC5 just to see if I was missing anything without any fiddling with the ADCIN result.

the reading is just constantly at 00255 (once in a blue moon it shows 511 then goes back to 255) on the LCD whether I hold the sensor or not, so somehing is seriously wrong with the way im setting it up, but I just cant for the life of me see what it is!

Same test with VDD as ref, I get values around 00046 - 00050 and when I hold the sensor, it rises.

Hope that may give some ideas as im all out now and I dont think tears and electronics mix lol!

[Mark J]

Boy do I feel a bit dumb lol!

Decided to have one more go this morning with the sensor and just displaying the result of all the samples added together with NO adjustments etc.

on the LCD it was showing something like 462 and putting the meter on the Gnd pin and the Vout pin on the sensor the meter was reading 231, so it then dawned on me that I dont need to do all the division stuff by the number of samples etc just simply divide by 2 to get the result!!!!!! DOH! and that way, I get the reading with the fractional degree's also!

Oh, and just using the VDD as the voltage reference.

One happy bunny!

[Mark J]

Well, I thought I had it working, but ive just had chance to work on the project again and found that when submersed in the aquarium (waterproofed obviously!) the thermomitor temp (tube type) shows a steady 25 C, yet the sensor on my project is all over the place (even have it in a bag in case of water seepage etc) it varies from between 22 to 28 degrees! and in a large body of water, there is no way the water temp can fluctuate so wildly (roughly 150 UK gallons)

So I am at a loss, as the code is based on other peoples posts and I thought it was working fine, but testing both sensors I still get the swings (Arghh!)

I am seriously getting annoyed with these sensors but with both swinging so much, it leads me to think its something in either my code, or getting some errenous readins through the breadboard etc.

Does anyone know if breadboards will cause these variations? as I have read somewhere that breadboards arnt exactly the greatest things etc.

Any ideas would greatly be appreciated!

[mackrackit]

Where the leads from the probe connect to the bread board. Place a 22uf , or something close, capacitor between the signal return and ground. This should settle things down. Long wires going to the probe will cause fluctuations like this.

[Mark J]

Cool thanks Dave,
It seems to have sorted the problem out.
As you can probably tell, the electronic side of things isnt my strong point lol! so many little things to think of etc.