AVR-Chat

It depends on what kind of output youre looking for
(voltage, current, resistance). Theres also LM135,
LM235, and LM335. There output is proportional to
either celcium, farenheit or kelvin. Ive used LM35
before but only for analog signals.
--- adiy@adis.on.ca <adiy@adis.on.ca> wrote:
> Hi,
> 
> Anybody have some ideas for sensing temperature and
controlling fans 
> depending on temperature? I am thinking about using
PWM to control fan 
> speed and multiple triggers to request fan action,
amongst them feedback 
> from a temperature sensor.
> 
> For sensors I am thinking of using a NTC thermistor,
DS1820 or LM35. To 
> set the threshold levels I could use a potentiometer
attached to an ADC 
> channel or binary coded jumpers/switches. 
> 
> Anything I missed? Anybody knows of app notes or
projects I could peak at 
> to get some ideas to get started? I suspect this
will be my first hands-on 
> AVR project.
> 
> Adi
> 
> 


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In MCUs DS18S20 is a much better solution than LM35 since it gets rid 
of the inaccuracies assiciated with ADC (though it is slightly 
expensive).
Resolution upto 0.0625 DegC can be obtained.
It comes calibrated and the output is digitized - no further 
calibration is required.
it comes in TO-92 package (the popular small transistor pack) which is 
very handy to integrate into a probe or similar application (ofcourse 
LM35 also comes in TO92).
NTC may turn out to be a headache on linearization (calibration).
If you are not worried about the precise reading, you can go for a 
thermistor(NTC/PTC)without linearization - but you need a current 
source to convert the resistance to a voltage and again the nuances 
associated with ADC.
The preference shall be DS18S20, LM35 & Thermistor in that order.

Instead of pot, you can use three buttons - UP, DOWN & ENTER if you 
have a means to display the setting - like LCD, 7 seg LED or Terminal.
If you are going for a blind controller then Pot is the solution.

A combination of DS18S20 and buttons will allow you to use AVRs 
without ADC like 2313

Compilers like FASTAVR, CODEVISION, BASCOM etc provide sample code for 
DS18S20, PWM, ADC etc.
Only you have to adopt codebits from different examples.
It just depends on your compiler

--- In AVR-Chat@yahoogroups.com, "Steven Chang-Lin Yu" <stevenyu@p...> 
wrote:
> There is also some other digital signal temperature sensor from 
maximum,
> national
etc.  Most of them are either 1wire or 2wire protocol

> 
>  
> 
> __________________________________________________________________
> Steven Chang-Lin Yu
> QUT EESE Student, Computer Technician
> ICQ#: 66369374
> 
> 
> Current ICQ status:  
> 
> 
> 
> * Home Tel#:  0401 0436 41
> * Work Tel#:  0401 0436 41
> *  HYPERLINK "http://wwp.icq.com/66369374"More ways to contact me 
> __________________________________________________________________
> 
> -----Original Message-----
> From: jay marante [mailto:jaythesis@y...] 
> Sent: Tuesday, 2 December 2003 3:24 PM
> To: AVR-Chat@yahoogroups.com
> Subject: Re: [AVR-Chat] Temperature Sensor Ideas
> 
>  
> 
> It depends on what kind of output youre looking for
> (voltage, current, resistance). Theres also LM135,
> LM235, and LM335. There output is proportional to
> either celcium, farenheit or kelvin. Ive used LM35
> before but only for analog signals.
> --- adiy@a... <adiy@a...> wrote:
> > Hi,
> > 
> > Anybody have some ideas for sensing temperature and
> controlling fans 
> > depending on temperature? I am thinking about using
> PWM to control fan 
> > speed and multiple triggers to request fan action,
> amongst them feedback 
> > from a temperature sensor.
> > 
> > For sensors I am thinking of using a NTC thermistor,
> DS1820 or LM35. To 
> > set the threshold levels I could use a potentiometer
> attached to an ADC 
> > channel or binary coded jumpers/switches. 
> > 
> > Anything I missed? Anybody knows of app notes or
> projects I could peak at 
> > to get some ideas to get started? I suspect this
> will be my first hands-on 
> > AVR project.
> > 
> > Adi

On Tue, 02 Dec 2003 10:26:03 -0000, you wrote:

>In MCUs DS18S20 is a much better solution than LM35 since it gets rid 
>of the inaccuracies assiciated with ADC (though it is slightly 
>expensive).
>Resolution upto 0.0625 DegC can be obtained.
>It comes calibrated and the output is digitized - no further 
>calibration is required.
>it comes in TO-92 package (the popular small transistor pack) which is 
>very handy to integrate into a probe or similar application (ofcourse 
>LM35 also comes in TO92).
>NTC may turn out to be a headache on linearization (calibration).
>If you are not worried about the precise reading, you can go for a 
>thermistor(NTC/PTC)without linearization - but you need a current 
>source to convert the resistance to a voltage and again the nuances 
>associated with ADC.
>The preference shall be DS18S20, LM35 & Thermistor in that order.

Unless you are going to production where cost is an issue, in which case the order of preference is
the reverse. 
Thermistors are very cheap, and their nonlinearity etc. can be taken care of in software easily
enough.

> Instead of pot, you can use three buttons - UP, DOWN & ENTER if you 
> have a means to display the setting - like LCD, 7 seg LED or Terminal.
> If you are going for a blind controller then Pot is the solution.

There is no display attached. So I need some means of setting the 
temperature. A pot would require bringing the temperature probe 
to the desired threshold temperature and then making the setting.
Another thought was to user DIP switches. Example  7 dip switches 
could cover set a temperature between 0 and 128 Celsius in 1 degree
steps.

I have all of the various temperature sensors I mentioned on hand. To
me it's a matter of pursuing the solution that's easiest to deal with
in software. I also have ATtiny26 on hand. So the ADC is there, but I 
don't have to use it.

Adi

Without a display, UP/DN buttons are out of the picture.
DIPSwitch is a good idea.
Just see that your MCU have sufficient free port pins - 7pins must be 
sufficient (depending on the range).
If you have all of them, simply go for DS18S20.
Timing is critical for 1-wire bus of DS18S20.
So dont try to write your own code in the begining.
Sample code is available for most compilers.


--- In AVR-Chat@yahoogroups.com, Adi Linden <adiy@a...> wrote:
> > Instead of pot, you can use three buttons - UP, DOWN & ENTER if 
you 
> > have a means to display the setting - like LCD, 7 seg LED or 
Terminal.
> > If you are going for a blind controller then Pot is the solution.
> 
> There is no display attached. So I need some means of setting the 
> temperature. A pot would require bringing the temperature probe 
> to the desired threshold temperature and then making the setting.
> Another thought was to user DIP switches. Example  7 dip switches 
> could cover set a temperature between 0 and 128 Celsius in 1 degree
> steps.
> 
> I have all of the various temperature sensors I mentioned on hand. 
To
> me it's a matter of pursuing the solution that's easiest to deal 
with
> in software. I also have ATtiny26 on hand. So the ADC is there, but 
I 

> don't have to use it.
> 
> Adi