How to interpret reading from LM335Z?

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aghazi

Junior Member level 2
lm335z

Hi,

I have one LM335Z attached to analog pin RA2 of 16F877A. Using ADCIN, i am getting the value and then displaying it on LCD using DEC. Value I am getting is 149. At this particular moment, the output voltage reading from LM335 is 2.982v. My question is how to interpret the value (149) i am getting from A/D channel? How can i convert it to °C reading? By the way room temperature at this moment is 25°C.

Regards,
AG

Davood Amerion

lm335z circuit

For optimum performance, with use of op-amp, you can align LM335 output range so that it fit to 0-5 volt.

for example you need to measure 0-125 deg centigrad.
make op-amp so that convert 2.73 to 0 volt and 3.98 (2.73+125*10mV/deg) to 5 volts.

Then use this formulla:

aghazi

Junior Member level 2
pic lm335z

hmmm. I am new to all this stuff but i do have a 741 opamp. Can you guide me how to attach/use it with lm335? Any schematic?

Thanks
AG

philba

Full Member level 2
using lm335z

it might be easier to take the read value and shift right by 2 bits (div 4).

another way to do this is to make Vref- be 2.73

it might be easier to take the read value and shift right by 2 bits (div 4).

another way to do this is to make Vref- be 2.73 and Vref+ be 3.73 and let the uC do the scaling. if super accuracy is not an issue you can use 2 dividers to get those voltages. I'd use 1% resistors.

If you wanted a wider range, you can make the range -50C to 150C (2.23 to 4.23), divide by 2 and then subtract 50.

silvio

lm335z

Quote from : https://tripoint.org/kevtris/Projects/peltier/

And the schematics :

https://tripoint.org/kevtris/Projects/peltier/images/Drink_Cooler_Schematic.gif

Take care of ADCON1 register (address 9Fh) settings of PCFG3-PCFG0 A/D port configuration control bits of PIC16F877A.
The anode of LM336 must be tied to pin RA3 (VREF+)
The common point of the two equal resistors 12k7 is tied to whatever analog input of PIC you choose.

The 12k7 value it's not important. It's a must to find two 1% matching resistors.

I believe that worth spending some money for LM336.
Just because:
- you don't have to do a messy conversion in software
- you don't have to use dividers for 2.73v and 3,73v by using 1% resistors of different values
- a minimum temperature drift because you'll not use +5v power supply as reference for VREF+ or to get 2.73v and 3.73v

However if you like to play with op-amp in Circuit Cellar issue 25 of february/march 1992 Mark Nurczyk shares from his experience.
You can find the article in bellow attachement:

soulraven

Newbie level 6
lm335z howto

i have find the solution for negative temperature with Lm335

temp_ulei = (adc_ulei * 0.48828) - 273.15;

this is the formula....

IGIF16

Junior Member level 2
thankssss mr.silvio

---------- Post added at 23:48 ---------- Previous post was at 23:47 ----------

thanks mr. soulraven

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