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'[PIC]:Could AN512 from Microchip be used to measur'
2001\01\05@100952 by Jose S. Samonte Jr.

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I was just wondering if AN512 from Microchip could be used to measure
temperature from 0 50 degrees, 0.1 resolution. Could it be? Could the source
code in the said application note be used in PIC16F84?
I hope you could help me. Thank you very much.

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2001\01\05@103950 by Michael Rigby-Jones

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> -----Original Message-----
> From: Jose S. Samonte Jr. [SMTP:.....dyoweeKILLspamspam@spam@USA.NET]
> Sent: Friday, January 05, 2001 3:11 PM
> To:   PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject:      [PIC]:Could AN512 from Microchip be used to measure 0 to 50
> degrees,  0.1 resolution?
>
> I was just wondering if AN512 from Microchip could be used to measure
> temperature from 0 50 degrees, 0.1 resolution. Could it be? Could the
> source
> code in the said application note be used in PIC16F84?
> I hope you could help me. Thank you very much.
>
50/0.1 = 500. That is just under 9 bits of resolution which is acheivable.
However, the accuracy (as compared to resolution) of the system will be
totaly dependant on how well you can linearise the thermistor.  An
interpolated lookup table may be the way to go.  You should read the recent
threads on using this technique, you will need an electrically quiet
environment and a well stabilised power source to get repeatable results.

How are you managing with the 24 bit ADC, async serial code, LCD code,
wireless data transmission and look-up tables?  You seem to have been very
busy recently :o)

Regards

Mike Rigby-Jones

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2001\01\05@232617 by Scott Beatty

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Jose

       You need to study the code by drawing a detailed flow chart of how the
program works.  The best way to start software design is to is to use a top-down

method.  This is where you draw a block diagram of your system and in
conjunction
with the PIC data sheets to get pins right.  Then you develop a block diagram
for the
software, breaking every individual job of the software into separate blocks.
Once
the block diagram is done you need to develop a flow chart for each block
individually.  once the flow charts are done writing the code is easy because
you are
writing a bunch of small programs instead of one big huge mess of text!
   I do not suggest that you use the code from AN512 unless you understand
every
aspect of it because if you have to tweak the program you may not do it right.
If a
problem develops from a change you will not be able to correct it without losing

precious time.
   I still suggest that you use a PIC with a built in A/D module.  The 16F877,
for
example, has eight 10-bit A/D ports available.  This would meet the .1 degree
accuracy and would be far easier to manage then a 24-bit serial A/D.  I must ask

why you decided to use a 24-bit converter.  This would only be necessary if you
were dealing with extreme!!! values.  Also I hope that your temperature probe
will
be is a temperature-stabilized environment, otherwise  anything after the radix
will
be constantly changing due to temperature changes.  A house thermostat, for
example, has a hysteresis effect to prevent it from turning the furnace or AC on

and off all the time.  On the other hand you could slow the program down to work

once every second, then you would have readable data on the display.  The look
up
table method that Mike mentioned is probably be best and most accurate way to
implement this project in assembler since you can't do any high level math in
one line
of code with assembler.  Also remember that it is also difficult to deal with a
radix
(decimal point) in assembler.  Even in high level languages a radix requires
floating
point math.
   If you answer my previous questions about your project I be able to help you
out.

Good Luck
Scott

"Jose S. Samonte Jr." wrote:

{Quote hidden}

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2001\01\06@005630 by David VanHorn

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I agree with this completely.

When you use someone else's code, you inherit their bugs, and you still
have to learn how it works.


Start writing down, in the form of assembler comments, what has to happen,
in order.
Start with big chunks, like maybe:

       ;Init the processor

       ;Init the ADC

Loop:
       ;Read the temperature

       ;Convert to degrees

       ;Output to display

Goto loop

Now, pick a module, and cut it into smaller pieces.
Eventually, you'll end up with code, and it will be pretty well commented
too :)

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