wanna convert values into centigrade

step size input adc 10bit

Hi everyone;
i am reading analog values from lm35(temprature IC) in pica6f877a.
I wanna know that how i convert these values in centigrade.
Range of lm35 is from 2 degrees centigrade to 150 degree centigrade and i want to read n display temprature from 2 degree to 50 degree centigrade and
also i am using 10-bit A/D converter.
plz tell me
Thanks

celcius to millivolt converter

hi
i think
voltage=ADC value *step size

stepsize for 10 bit=5/1024 if 5v if reference
Shakeel

lm35 wrong values

thanx shakeel
but i am still confuse. i am not getting ur point properly.
if i use the formula as u say

ADC value=(v input (lm35 output) * 1024)/vref

Click to expand...

i am using this like that
but i am not getting the right value.
Is there any other way to read n convert values into centigrade

maximum centigrade value

You've to fit the input signal to the ADC converter dynamic, in other word, your PIC ADC can give 10 bit word from a signal between 0 and 5V then at first you need to fit the analog signal with the input range of the used ADC.
If you like to measure a temperature value between 2 °C to 150 °C look at the LM35 specification, if you're using the first schematic (Figure 1 into the datasheet) you have 10 mV every °C then 2 °C -> 20mV, for 150 °C you should be able to read 1.5 V.
Now you've a problem, for a 10 bit DAC you've a minimum of 5/1024=4.88 mV then you should be able to read 20 mV and correct understand it, but the maximum value of your interval is only 1.5 V, less than the maximum allowable of 5V then your reading will be compress because 20 mV is approx equal to a digital value 4 and 1.5 V is equal to 307.2 a total range of about 303 digital value regard a total available of 1024. You need to fit the analog signal to the 0 - 5 V range, or better from 0.5 to 4 V, to do this use operational amplifier and then make the needed calculation into the microcontroller.

As other way you can use inexpensive digital termometer LM70 with SPI interface, precision is 0.25 °C for a temperature range between -55 to +150 °C, with this device no need to use ADC or other amplifier, simply read the digital value and make your scaling calculation inside the microcontroller.

**broken link removed**
**broken link removed**

Hope it help

Bye
Powermos

convert millivolt to celcius

Thanks TekUT
if i simply do this then would it be right or wrong or display right or wrong values
my code is as follows

void main()
{
int16 value,value1;
setup_adc_ports(ALL_ANALOG);
setup_adc(ADC_CLOCK_INTERNAL);
while(1)
{
set_adc_channel(2);
delay_ms(500);
value=read_adc();
value1=5*value*100/1023;
printf("%f\r\n",(float)value1);
}
}

Click to expand...

one more thing it takes 10mV for 1 step.can i reduce it to 5mV.

how to convert lm35 to centigrade?

Could you post the resulted data after conversion and the related voltage value at the input of the ADC pin?

Bye
Powermos

lm70 calculation

the resulted data is when my room temp is 27

27.34
27.34
27.83
27.83
.
.
.
.



when i increase the temp by means of place soldering iron near lm35 the temprature raises.

the voltage at the input of adc is approx274.78mV
is this calculation is right.
i think it is wrong but i am not sure