LM75 Help please

[AtomSoft]

sure but in a bit. i haveto get son from daycare. You just reminded me about ADCON1 there... i need to check if i set it to digital. im sure i did but heh you never know.

The LM75 i got was a sample. They sent me 2 for free since i buy from mouser a lot.

The MCU im using is a PIC18F2525. Im using the SCL and SDA lines i think .. i know its RC3 and RC4.

The Address lines A0:A2 are grounded. Not pull down (straight to gnd). The GND is gnd and the VS+ is 5v.

The OS line isnt connected at all. Ill make a schematic when i come back ok. or maybe now since i got 30 min until i leave. Let me see if i can draw one up fast.

 

[AtomSoft]

Here is my schem:

 

[AtomSoft]

using:

    temp*=9;
    temp/=5;
    temp+=64;

With the gnd connected to IC i get 480F lol and with ground off i get about 81F

 

[DirtyLude]

Can you post the circuit how you interfacing the LM75 to PIC pin? What PIC you using, can you measure the voltage at the output pin of LM75 with and without connecting it to the PIC A/D input?

-Raj
Experiments with PIC16F628A

Maybe you should look at the datasheet and previous conversation before trying to help. LM75 is a digital temp sensor, not a analogue one.

I wouldn't mind seeing all the code again to see if I can figure out what's going on. I'm having trouble fitting the pieces that have been posted together. Pommie's code is using 9bits, which gives 0.5 deg resolution.

I'm using 11bits, but I don't need to convert to Fahrenheit so calculation is not such a big deal for me.

 

[AtomSoft]

Ill post a zip:

The Proteus stuff is just crap from another project heh dont mind it

 

[AtomSoft]

ok i replaced the IC with the second one and it shows 52.5F with ground and 81.5F with out gnd

 

[DirtyLude]

I don't see anything specific with the code itself.

Does the temp reading change when you put your finger on the chip to warm it up, or is the reading static?

My Math is terrrible. I'll put your fahrenheit conversion into my own code tonight and try it out.

I have to say, using the logic analyser with the protocol analysis has made this kind of debugging so much easier for me. I gave up on so many of these things before I was able to just look at what I was getting and have it explained using the analysis software what's going on.

 

[AtomSoft]

heh i need to get me one of those :



But never remember to save the money for it heh....

The temp is always fluctuating from 81F-82.5F

When i place my finger on the device it changes a few degrees to about 83F-85F

 

[rajbex]

Maybe you should look at the datasheet and previous conversation before trying to help. LM75 is a digital temp sensor, not a analogue one.

I wouldn't mind seeing all the code again to see if I can figure out what's going on. I'm having trouble fitting the pieces that have been posted together. Pommie's code is using 9bits, which gives 0.5 deg resolution.

I'm using 11bits, but I don't need to convert to Fahrenheit so calculation is not such a big deal for me.

Sorry, Mark. I totally messed it up with another post that uses LM35. You are right, LM75 is a digital sensor.
- Raj
Experiments with PIC16F628A

 

[AtomSoft]

Thanks tho Raj.. I like the fact you tried to help at least. i rather have someone jump in than just look heh ... thanks again


Nice Blog!