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Topic: LM35D ¿Good? (Read 1 time)previous topic - next topic

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Dec 05, 2012, 05:14 pm
http://www.ti.com/lit/ds/symlink/lm35.pdf

Page: 6 .Graphic: Minimum Supply Voltage vs. Temperature.

The graph shows the voltage discontinuities at certain temperatures. The slope increases with increasing current. Arduino generates a voltage of 5.01 V.

How I can I know that there are no discontinuities in voltage between +2 º, +100 º C?
I see in the graph where the discontinuities begin to 2 mA, but I do not see where the discontinuities with 40 mA.

dhenry

#1
Dec 05, 2012, 05:44 pm
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How I can I know that there are no discontinuities in voltage between +2 º, +100 º C?

Typically done by reading the datasheet or experimenting with the chip.

Grumpy_Mike

#2
Dec 05, 2012, 06:00 pm
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The graph shows the voltage discontinuities at certain temperatures.

No it doesn't.

The dotted line indicates that the chip is operating outside it's recommended parameters, not that there is a discontinuity in reading.

Nice useful post as normal from dhenery.

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#3
Dec 05, 2012, 06:38 pm
Can you tell me why there is a 5?

samples = (5.0* analogRead(pin) * 100.0) / 1024.0;

for this device.

100ºC = 1024 points

Tª = (points * 100) / 1024

Why you should add 5?

Grumpy_Mike

#4
Dec 05, 2012, 06:48 pm
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Why you should add 5?

You are not adding 5V you are multiplying by 5V.

An analogue reading returns a number from 0 to 1203, this corresponds to a voltage between 0 to 5V so this:-
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samples = (5.0* analogRead(pin) * 100.0) / 1024.0;

Is converting the number you read into a voltage.

dhenry

#5
Dec 05, 2012, 06:52 pm
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samples = (5.0* analogRead(pin) * 100.0) / 1024.0;

Things like that utilize floating point math and floating point math is quite inefficient on an 8-bit mcu.

A simpler approach would be to use fixed point math.

Grumpy_Mike

#6
Dec 05, 2012, 07:22 pm

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samples = (5.0* analogRead(pin) * 100.0) / 1024.0;

Things like that utilize floating point math and floating point math is quite inefficient on an 8-bit mcu.

A simpler approach would be to use fixed point math.

No it is not a simpler approach it is an approach that runs faster.
We are dealing with a compiler here and simple projects. All those posts and you still haven't got the basic hang of this forum have you.

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