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LM335 problem

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matpaa

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Hi !
I'm noob what comes with electronics, so here we go ...

Problem is that LM335 temperature sensor should give about 3 volt from Vout, but i get 4.8 volt in room temperature.
Also, there is only very little change about voltage readings (from ADC) even temperature change is 10 - 20 centigrade.
ADC is working properly and i get sensible readings from there.

LM335 is connected to PC18F452 ADC (RA0)

VDD +5V ------ 2.2Kohm -----/--- pin1 at LM335 (the left one)
RA0 -------------------------/
Ground ---------------------------pin2 at LM335 (the middle one)
pin3 at LM335 is not connected

I hope you can help me with this.

PS. i also try another sensor with similar problems, so apparently it is't the sensor or then i'm keep killing those ;)
 
Last edited:
matpaa said:
Hi !
I'm noob what comes with electronics, so here we go ...

Problem is that LM335 temperature sensor should give about 3 volt from Vout, but i get 4.8 volt in room temperature.
Also, there is only very little change about voltage readings (from ADC) even temperature change is 10 - 20 centigrade.
ADC is working properly and i get sensible readings from there.

LM335 is connected to PC18F452 ADC (RA0)

VDD +5V ------ 2.2Kohm -----/--- pin1 at LM335 (the left one)
RA0 -------------------------/
Ground ---------------------------pin2 at LM335 (the middle one)
pin3 at LM335 is not connected

I hope you can help me with this.

PS. i also try another sensor with similar problems, so apparently it is't the sensor or then i'm keep killing those ;)
Why are you connecting pin 2 to GND? The datasheet I looked at clearly shows that pin 3 should be grounded, with pin 2 floating.
 
If you are using the TO-92 package, I think the connections should be
left pin,(marked adj) NC
center pin,(marked +) to Pic, 2.2k to 5V
right pin, (marked -)GND
All looking at the bottom with the flat side up.
 
k7elp60 said:
If you are using the TO-92 package, I think the connections should be
left pin,(marked adj) NC
center pin,(marked +) to Pic, 2.2k to 5V
right pin, (marked -)GND
All looking at the bottom with the flat side up.
I agree. The datasheet I referenced has very odd pin numbering on the schematic diagram, which is where I got the pin numbers.
 
Oops ... little typo

Sorry Roff and k7elp60 about incorrect information, but it was 3 am when i was writing that :eek:
I can't understand how i ever could wrote pin order like that even components are front of my eyes.:rolleyes:

So, here is correct diagram (that i actually had and still have)

Ground -------------------------- V- pin at LM335
VDD +5V ------ 2.2Kohm -----/--- V+ pin at LM335 (the middle one)
RA0 -------------------------/
Adj pin at LM335 is not connected

And yes, it's TO-92

I wish you still can work with this little problem.
 
matpaa said:
Problem is that LM335 temperature sensor should give about 3 volt from Vout, but i get 4.8 volt in room temperature.

How can you be sure that you are not "driving" the PIC RA0 pin with logic HIGH?

Can you disconnect the connection of LM335 to the 18F452 and see if this is the problem?
 
eblc1388:
I think that too and measured RA0 pin voltage and that shows 0,6 volt.
I just forgot to mention that. However i did't measure voltage from LM335.

Now i rechecked and measured from LM335 Vout and get the same 4.8 volt as before when Vout was connected to RA0.

So, problem stays unsolved ;)
 
Use new parts. It is possible you have killed them both.

Next time before you place the new LM335 into the circuit, substitute it for the moment by a 2K2 resistor instead.

If you cannot measure 2.5V from it, then there is still something wrong with the circuit setup.

If you get 2.5V with a simple resistor, then there is no way you can kill the new LM335 even if you inserted it the wrong way round into the circuit.
 
eblc1388 said:
Use new parts. It is possible you have killed them both.

Next time before you place the new LM335 into the circuit, substitute it for the moment by a 2K2 resistor instead.

If you cannot measure 2.5V from it, then there is still something wrong with the circuit setup.

If you get 2.5V with a simple resistor, then there is no way you can kill the new LM335 even if you inserted it the wrong way round into the circuit.
Thanks, i try this soon as i get back to home. :)
 
Before you have checked out fully the PIC software, I would advise using an additional 2K2 series resistor between the LM335 and the ADC RA0 of the PIC. This would prevent damage to LM335 if somehow you have program the PIC pin to output a digital HIGH logic level instead. It is just a precaution.

So you'll need two resistors, one to connect between +5V and LM335 and one between LM335 and PIC.

This additional resistor can be removed later if everything checks out.
 
Problem solved

Right.

I got little help from company i bought PCB-kit and parts.
They made small, but obviously important mistake when they wrote instructions to LM335 ... left and right has change places, so my actual connections was Ground pin - not connected and Adjustment pin to ground.

This was confusing me even then when i was reading datasheet.
Now it make sense that datasheet picture should read as looking up to component,
not as it would be in PCB.:p

I guess i learn something about this. :rolleyes:

Thank you all for your help, especially eblc1388
 
Thanks!

Thanks for the "inverted datasheet diagram mistake". I'd never imagined something like that.
The LM335z is working perfectly now.
 
This is quite old but I just encountered the same problem.

There's NO mistake in the datasheet.

It clearly states: "Bottom view".
 
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