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I'm wondering which benefits/downsides I have using following thermometer? Is there something I'm overseeing? For easy temperature measuring, what would be the easiest? My Opinion is LM35, am I right? When should I use which of them?

I don't have any experience with electrical engineering (so it might be that the question is very basic)

I would appreciate if you could suggest some Contra points for each thermometers

LM35

Pro

  • Easy to calculate: Temp = (Vout - 500) / 10
  • Accurate enough & cheap

Contra

  • nothing negative?

Thermistor

Pro

  • Accurate & cheap

Contra

  • Non linear; Have to use Steinhart-Hart-Equation to calculate the temperature

Alternatives

1-Wire

Pro - Digital (is that a pro point?) so basically just reading the temperature

Contra - compared to the others very expensive

Can you suggest me any other temperature sensors and tell me more downsides of the above listed ones?

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    \$\begingroup\$ Thermistors can be obtained with +-0.1C accuracy which is hard to find with the chip sensors. \$\endgroup\$ Apr 4 '15 at 12:59
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or an absolute sensor like the LM35 (or LM335) you need a microcontroller with an A/D converter, and a voltage reference that is accurate enough (USB power, or an 7805 regulator will in most cases NOT be accurate enough).

A resistor can be used as ratiometric sensor, which means that you don't need an absolute voltage reference, but as you indicate, the conversion from what you measure to temperature is far from linear.

Unless there are strong reasons not to do so, I would suggest a temperature sensor with a digital interface. That still leaves lots to choose from, like the 1-wire DS18xx you hint at, the I2C LM75 or TCN75, or the SPI TC74, to name just a few.

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  • \$\begingroup\$ So a custom battery would not work as power source for a LM35 when I need an accurate result as I assume that the battery does not provide a constant voltage, right? \$\endgroup\$
    – Michael
    Apr 4 '15 at 16:59
  • \$\begingroup\$ Correct. A battery would be OK as power source, but when you don't kwno whether it delivers 3 * 1.55 = 4.65 V or 3 * 1.2 = 3.6 V you will get a very large uncertainty in the measured temperature, because the AD will (without any other reference) measures the voltage as a percentage of the power supply. (There are microcontrollers that have a built-in reference, but do check its accuracy first!) \$\endgroup\$ Apr 4 '15 at 17:38
  • \$\begingroup\$ I'm currently evaluating what to use for a distributed heat/smoke sensor system and the TCN75 comes very handy with all the built in functionality and the hysteresis. Thanks for pointing him out! \$\endgroup\$
    – Michael
    Apr 4 '15 at 18:20

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