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Topic: LM335 Temperature Sensor Help (Read 2266 times) previous topic - next topic

SSzretter

I have an LM335 temperature sensor and am trying to figure out why it gives values that bounce around 15 degrees or more.

It hooked up to my Analog 0.   I am using the analogRead(A0);

I am not using the adjust pin on the sensor, negative pin is connected to arduino gnd.

Positive pin connected through 2.2k to arduino 5v.

A0 connected to positive pin.

My readings come back somewhat accurate - sometimes - for example, maybe 4-5 readings - then suddenly it might drop (or rise) 5, 10 or even 15 degrees!

Well, the raw "K" reading from the sensor is a difference of 2, 3, 4 +.

Any thoughts as to why the sensor is so wacky?   According to the LM335 spec, it looks like the adj pin is ok not connected.     Is 2.2k a valid resistance?



SSzretter

The K value jumps around too.    To get to C and F, I just multiply the K value.
So for example, I might see a K value of 6, then 8, then 3, then 9...

Could I put a resistor in place instead of a pot?

Snowman

I have noticed this it the past as well. It is easy to fix by decoupling, I used a 0.1uf cap
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

SSzretter

I will try some different resistor values for the 5v.    I tried placing 2 static resistors to the adj pin, did not seem to make any (or much) difference.

Here is  a picture of what it looks like - the red plot is the value of the lm335 analog read (after dtstrf).

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