need to add temperature display using LM335

[prosound90]

hi guys

i think it will be easier to put this in a new topic instead of the 2 pages topic for the clock AN590.

the clock is working fine thanks to your help .

i need to add temperature display , i have a bunch of LM335 i bought a

long time ago and i like to interface it with the 16F877.

i hve a schematic that i downloaded from the internet ,dose this one work???, (i know it use LM34).



i have AN0,AN2,and AN3 available ,

do i need to use an OPAMP for the signal or it can be inerfaced directly

if any one have a schematic please post it.

iam thinking of a scale from -20C to 50C or ,and 0-120 F

thanks for your help.

 

[williB]

https://www.electro-tech-online.com/custompdfs/2004/12/LM135.pdf

With less than 1 ohm dynamic
impedance the device operates over a current range
of 400 µA to 5 mA with virtually no change in performance.

so if you can keep tjhe current through the device to less than 5mA you should be fine..
yes you should be able to interface it directly..

 

[williB]

i am not understanding what you are outputting ..
you only need to read analog from the device..

 

[prosound90]

thats a shcematic from somebody was using this interface with a 16F628 and a LCD i dont know if it works or not ...thats why iam asking if it works like that .

i think the output is for (V) refrance.

 

[williB]

i would connect Pin 13 of your schematic , to where it says output in my schematic..

 

[williB]

I dont know where they got their info from , but there isnt anything resembling that type of hook up in the National specs for the LM 34..
https://www.electro-tech-online.com/custompdfs/2004/12/LM34.pdf

 

[prosound90]

iam going to use your schematic with LM335

in my project .


is it going to be ok to use the VDD for refrence for the scale that i need?

 

[spirosd]

Sorry for butting in, on your thread prosound90. I am working on a similar req. for my project and was planning to use an LM35.

On the datashet the circuit below gives full range -55C to +150C
Could I confirm:
> If V+ is 5V V- is ground R1 should be 1K Ohms? ( -V == -5V? )
> I could hook up Vout directly to ADC pin on 16f877?

Thanks
Spiros

 

[williB]

iam going to use your schematic with LM335

in my project .


is it going to be ok to use the VDD for refrence for the scale that i need?

so V+/.005
or your V+/.004 =R1..
might as well not bring I to the max..
even 1 mA would work great ..

 

[williB]

Sorry for butting in, on your thread prosound90. I am working on a similar req. for my project and was planning to use an LM35.

On the datashet the circuit below gives full range -55C to +150C
Could I confirm:
> If V+ is 5V V- is ground R1 should be 1K Ohms? ( -V == -5V? )
> I could hook up Vout directly to ADC pin on 16f877?

Thanks
Spiros

do you have -5V available ..if not, dont use a resistor..
if you do , -5/50 microamps = 10K ohms..

i dont think yours needs a resistor for 2 centegrade to 150 C..

but to get the full range they recommend..>
Choose R1 = −VS/50 µA
V OUT=+1,500 mV at +150°C
= +250 mV at +25°C
= −550 mV at −55°C

I could hook up Vout directly to ADC pin on 16f877?

i dont see why not..

 

[spirosd]

Thank you for your reply williB.

I need the negative temps so I have to try and use the full range.

do you have -5V available ..if not, dont use a resistor.. if you do , -5/50 microamps = 10K ohms..

I do not have -5V available, so I presume I can not use that circuit.

The datasheet also has this circuit .... the -ve output voltage confuses me. How would I use that circuit with a pic?

Thanks
Spiros

 

[williB]

it looks like they are expecting you to use an op Amp on the + and -

 

[fabbie]

im curious about this, if the LM35 is placed in a freezer, will the voltage output immediately drop to 0 V?

Im having a strange problem, no matter where i place my LM35 the temperature range is always between 25 C to 35 C.

I grounded my -Vs in this case, since i dont require any negative voltage

 

[williB]

im curious about this, if the LM35 is placed in a freezer, will the voltage output immediately drop to 0 V?

Im having a strange problem, no matter where i place my LM35 the temperature range is always between 25 C to 35 C.

I grounded my -Vs in this case, since i dont require any negative voltage

where did you ground the LM35..??which picture?

 

[prosound90]

hi

i want to aske a diffrent qusetion now?

what consederation should i keep in mined when adding an analoge reading to my project you know(a clock) and iam adding a temeperature reading to it.

because the ADC takes long time to get result iam worried about the clock losing time as it has to stop to get ADC reading.

what do you recomend the interuput way or A CALL to the ADC ,(read,display,then go back to time count)

do i have to compensate for the time that the ADC use so the clock dose not loose count ?

can i use the same (tmr0 for both) or its better to use (tmr1 free running for the time on 32khz) ? and 4mhz for the PIC.

thank you

 

[Nigel Goodwin]

hi

i want to aske a diffrent qusetion now?

what consederation should i keep in mined when adding an analoge reading to my project you know(a clock) and iam adding a temeperature reading to it.

because the ADC takes long time to get result iam worried about the clock losing time as it has to stop to get ADC reading.

what do you recomend the interuput way or A CALL to the ADC ,(read,display,then go back to time count)

do i have to compensate for the time that the ADC use so the clock dose not loose count ?

can i use the same (tmr0 for both) or its better to use (tmr1 free running for the time on 32khz) ? and 4mhz for the PIC.

thank you

The time to take an analogue reading is only small, but as you say it will add up over time - but you shouldn't really be trying to run a clock in a software loop.

As you suggested, the answer is to use timer interrupts to run the clock, I would suggest you use tmr2, tmr0 has latency problems, and you have to correct for those. Another option is to use an external clokck chip, one of my tutorials uses a battery backed I2C chip from Philips, but there are various others.