Temperature does not go below 0

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- 4th June 2015, 13:46
amodpathak

Temperature does not go below 0

IAM MAKING TEMPERATURE CONTROLLER USING ntc THERMISTOR FROM -10 DEGREE TO 50 DEGREE.BUT MY TEMPERATURE IS NOT GOING BELOW 0. PLS CHECK MY CODE AND GUIDE ME.THANKS

Code:

DG1 VAR BYTE DG2 VAR BYTE DG3 VAR BYTE DIGIT VAR BYTE DG VAR BYTE COUNTT VAR BYTE NUMB VAR WORD N VAR WORD adval var word temp var word TEMPP VAR WORD ADCON1=%10000000 adcon0=%00000101 TRISA=1 TRISB=%00111000 TRISC=0 numb=0 gosub mread 'n=numb GOSUB DIGITCALC '------------------------------------------------------------------------- MAIN1: GOSUB DISPLAY IF PORTB.3=1 THEN MREAD IF PORTB.3=0 THEN MAIN GOTO MAIN1 '------------------------------------------------------------------------- MAIN: ADCON0.2=1 GO: IF ADCON0.2=1 THEN GO adval.HIGHBYTE = ADRESH adval.lowbyte = ADRESL temp=adval N=temp gosub display gosub digitcalc If adval>NUMB then PORTB.7=0 IF ADVAL< NUMB-5 THEN PORTB.7=1 GOTO MAIN1 '_____________________________________ UP: IF NUMB=50 THEN MAIN NUMB=NUMB+1 N=NUMB GOSUB DIGITCALC IF PORTB.4=1 THEN MEMORY GOTO MAIN1 memory: WRITE 0,numb.HighByte WRITE 1,numb.LowByte GOTO MAIN1 '_____________________________________ DOWN: IF NUMB=-10 THEN MAIN 'MIN LIMIT NUMB=NUMB-1 N=NUMB GOSUB DIGITCALC IF PORTB.5=1 THEN MEMORY GOTO MAIN1 '_____________________________________ MREAD: READ 0,numb.HighByte READ 1,numb.LowByte n=numb gosub digitcalc IF PORTB.4=1 THEN UP IF PORTB.5=1 THEN DOWN goto main1 ___________________________________________________ DISPLAY: FOR COUNTT=0 TO 99 PORTC=DG1 PORTB.2=1 PAUSEUS 300 PORTB.2=0 PORTC=DG2 PORTB.1=1 PAUSEUS 300 PORTB.1=0 PORTC=DG3 PORTB.0=1 PAUSEUS 300 PORTB.0=0 NEXT COUNTT RETURN '________________________________________________________________ '__________________________________________________________________________ DIGITCALC: DIGIT=0 LP1: IF N<100 THEN DS1 N=N-100 DIGIT=DIGIT+1 GOTO LP1 DS1: GOSUB FND DG1=DG DIGIT=0 LP2: IF N<10 THEN DS2 N=N-10 DIGIT=DIGIT+1 GOTO LP2 DS2: GOSUB FND DG2=DG DIGIT=N GOSUB FND DG3=DG RETURN '__________________________________________________________________________ '__________________________________________________________________________ FND: FND0: IF DIGIT>0 THEN FND1 DG=$7E '%0111 1110 GOTO FNDEND FND1: IF DIGIT>1 THEN FND2 DG=$48 '%0100 1000 GOTO FNDEND FND2: IF DIGIT>2 THEN FND3 DG=$3D '%0011 1101 GOTO FNDEND FND3: IF DIGIT>3 THEN FND4 DG=$6D '%0110 1101 GOTO FNDEND FND4: IF DIGIT>4 THEN FND5 DG=$4B '%0100 0011 GOTO FNDEND FND5: IF DIGIT>5 THEN FND6 DG=$67 '%0110 0111 GOTO FNDEND FND6: IF DIGIT>6 THEN FND7 DG=$77 '%0111 0111 GOTO FNDEND FND7: IF DIGIT>7 THEN FND8 DG=$4C '%0100 1100 GOTO FNDEND FND8: IF DIGIT>8 THEN FND9 DG=$7F '%0111 1111 GOTO FNDEND FND9: DG=$6F '%0110 1111 FNDEND: RETURN

'_________________________________________________ _________________________
- 4th June 2015, 13:57
HenrikOlsson

Re: Temperature does not go below 0

Hi,
With PBP variables declared as BIT, BYTE and WORD are unsigned, they are always treated as positive.
Of course you can handle that yourself with something like.

Code:

IF NUMB.15=1 THEN ' MSB set, value is negative IF ABS NUMB=10 THEN MAIN ' MIN LIMIT ENDIF

/Henrik.
- 4th June 2015, 14:35
amodpathak

1 Attachment(s)

Re: Temperature does not go below 0

i tried that code but again temp is not going below 0.No minus sign.Attachment 7848
- 4th June 2015, 17:26
Scampy

Re: Temperature does not go below 0

I always add comments to my listings, which also helps others follow the code and my "logic" when I have issues and post the code up seeking advice. I find it hard to work through the OP's code, but if you are using A-D I'm presuming that 0volts would equate to 0 and 5v 255, or something like that. I'm thinking that you need to scale the range or something so that, for example 127 digital (2.5v approx in this example) would be 0 degrees, and that any value between 0 and 127 would be treated as a minus value ? Then using the if then statement similar to if value is less than or equal to 126 then place the - symbol in the 1st LED,
- 4th June 2015, 18:26
Archangel

Use Code Tags

[code] Your Code Goes Here [/code]
- 4th June 2015, 18:39
amodpathak

Re: Temperature does not go below 0

Thanks Scampy for clearing my doubts .what you explained is very easy to understand..thanks & regards
- 4th June 2015, 20:49
amodpathak

Re: Temperature does not go below 0

An example needed.iam using 10 bit adc and sensor is 10k thermistor.
- 5th June 2015, 07:40
EarlyBird2

Re: Temperature does not go below 0

Quote:

Originally Posted by amodpathak

An example needed.iam using 10 bit adc and sensor is 10k thermistor.

A Thermistor changes resistance with temperature change. To read a 'remote' Thermistor a 'completion resistor' (CR), typically 1000 ohms, is used in series and a known voltage is applied to the circuit then the voltage drop across the CR is measured. If the thermistor is on the board then voltage drop across the Thermistor can be measured directly. The resistance changes with temperature change which is not linear and this is required

http://en.wikipedia.org/wiki/Thermistor#NTC

Quote:

Steinhart–Hart equation

For accurate temperature measurements, the resistance/temperature curve of the device must be described in more detail. The Steinhart–Hart equation is a widely used third-order approximation:
1 \ T = a + b\,\ln(R) + c\,(\ln(R))^3
where a, b and c are called the Steinhart–Hart parameters, and must be specified for each device. T is the absolute temperature and R is the resistance.

As you can see natural logarithms are needed to use this conversion, which are not available with PBP.
- 5th June 2015, 21:12
Scampy

Re: Temperature does not go below 0

Why not use a DS18B20 - It would be a lot simpler going digital
- 6th June 2015, 13:51
Charlie

Re: Temperature does not go below 0

Quote:

As you can see natural logarithms are needed to use this conversion, which are not available with PBP.

Or you could simply use a look-up table...
- 6th June 2015, 21:42
amodpathak

Re: Temperature does not go below 0

Not able to solve problem.tried many times.
- 9th June 2015, 14:04
AvionicsMaster1

Re: Temperature does not go below 0

Does temp read correctly above zero? 'shows sensor connected and only negative indication of code is incorrect

Can you make the LED blink? 'shows PIC and LED hooked up correctly and working

I'm a novice programmer but aren't you supposed to RETURN from a sub then GOTO a different subroutine? Most of your FNDx routines GOTO a sub for a RETURN. The first FND is empty. The blinking LED would tell you if the program is stuck somewhere.

In DIGITCALC won't the variable N always be a negative number? If so PicBasic will always report that as a zero.

Hope it helps and I don't get flamed too much?
- 9th June 2015, 17:35
Scampy

Re: Temperature does not go below 0

Quote:

Originally Posted by AvionicsMaster1

I'm a novice programmer but aren't you supposed to RETURN from a sub then GOTO a different subroutine? Most of your FNDx routines GOTO a sub for a RETURN. The first FND is empty. The blinking LED would tell you if the program is stuck somewhere.

In DIGITCALC won't the variable N always be a negative number? If so PicBasic will always report that as a zero.

Hope it helps and I don't get flamed too much?

His code is messy with no comments and lots of spaces so it does make it hard to follow, but there is a FND start and finish.

Code:

FND8: IF DIGIT>8 THEN FND9 DG=$7F '%0111 1111 GOTO FNDEND FND9: DG=$6F '%0110 1111 FNDEND: RETURN

Basically the program go's to the subroutine FND, which then contains a lot of IF DIGIT statements and if it is above a value then jump to the next FNDx label, but if it equals that value then set set value for DG and goto FNDEND, which is a simple RETURN and thus closes the subroutine.
- 10th June 2015, 16:22
AvionicsMaster1

Re: Temperature does not go below 0

Thanks for the schooling. I see it now. Though it would be interesting to know if it indicates anything other than zeroes.

I usually use the LED blinking to help me know when I've done something less than desirable. Just add a TOGGLE to the main loop and a short pause will let you know if the program's hung.

Best of luck.
- 10th June 2015, 20:24
amodpathak

Re: Temperature does not go below 0

Temperature goes above ZERO.Positive temperature is displayed correctly.When i keep thermistor in freezeo then temperature does't go below ZERO.
- 11th June 2015, 01:00
Scampy

Re: Temperature does not go below 0

Quote:

Originally Posted by amodpathak

Temperature goes above ZERO.Positive temperature is displayed correctly.When i keep thermistor in freezeo then temperature does't go below ZERO.

Try some basic measurements. remove the thermistor from the board and place it in your freezer with wires connected. Measure the resistance using a digital volt meter and note it down, together with the temperature. Repeat the measurement when the thermistor is placed in ice water, and again when under a lamp or something that you can measure the temperature with. This may help you calibrate the routine better.

One possible issue could be that your chosen thermistor is positive only, ie at zero degrees C it's resistance is zero ohms (or as near to as dam it).
- 11th June 2015, 14:56
Charlie

Re: Temperature does not go below 0

Without the datasheet for your device, it's impossible to resolve it for you, but here's the data for a typical device:
http://www.arroyoinstruments.com/thermistors.html It has a table of values vs temperature. So, at -10C it's about 55Kohm, and at +50C it's about 3.6K ohms. So now you need to turn that into a voltage either using a resistor divider, or a current source. This is simple math, easy to do with Excel, and you can create a list of voltages for each degree or half degree or whatever you like. Then use those voltage values to lookup the corresponding temperature.