adc and lm35: do i need opamp?

Thread Starter

efm

Joined Sep 14, 2006
14
hello,
i'm an electronic newbie, so a help would be really appreciated here :)

i'm making a project that includes a lm35d and a adc0808,
from articles on the net, i read that the lm35d needs opamp before the output goes to adc0808's input,

my questions are:

1. is it possible to do it without opamp?
2. can i connect the lm35d's output to adc0808's input?
3. if i set the vref of the adc to 2.5 v, can it be possible to connect lm35d without opamp?
4. or, do you guys have any suggestion?

thank you,
faizal
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

National's big claim for the LM35 is a low output impedance, so yes, you can attach it to the A to D directly.

There is always the matter of scaling though. If you want to get the full range of the LM35 into the A to D, then you may need to add an op amp for some tailored amplification.

Without any idead of what accuracy you need, or range of temperatures to respond to, it's pretty hard to get more specific.
 

Thread Starter

efm

Joined Sep 14, 2006
14
Hi, beenthere, thanks for the reply,

so, I still can use LM35 without A/D? but perhaps the output I get by doing it is around 1 V only (as
100 Celcius is 1 V)?

anyway, I've decided to use an OpAmp. I'm going to use three LM35s, is a LM324 (quad operational
amplifier) suitable enough for it instead of LM358 (three LM358s?)

thank you,
faizal
 

mozikluv

Joined Jan 22, 2004
1,437
hi,

the lm324 will do better than 3 lm358. temperature effect on the lm324 will illicit practically the same reaction, while the individual lm358 will react to temperature not in the same way as the lm324.

moz
 
please i need info abt the signal conditioning ckt of lm35

hello,
i'm an electronic newbie, so a help would be really appreciated here :)

i'm making a project that includes a lm35d and a adc0808,
from articles on the net, i read that the lm35d needs opamp before the output goes to adc0808's input,

my questions are:

1. is it possible to do it without opamp?
2. can i connect the lm35d's output to adc0808's input?
3. if i set the vref of the adc to 2.5 v, can it be possible to connect lm35d without opamp?
4. or, do you guys have any suggestion?

thank you,
faizal
 
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