Need some opinions on temperature sensor

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McMurry

Joined: 16 Feb 2008
Posts: 75

19 May 2008 19:23 sample code for temperature sensor

I am currently working on a project that will give temperature reading.

Is there any disadvantage of using microcontroller with built in temperature sensor instead of using external temperature sensor?
does external temperature sensor give a more accurate reading? and respond to temperature changes more rapidly?

also, is there any disadvantage of using a temperature sensor that gives digital output, instead of analog temperature sensor? (other than the cost factor)

FvM

Joined: 22 Jan 2008
Posts: 5154
Helped: 766
Location: Bochum, Germany

19 May 2008 20:19 not foundnot found1

The temperature error caused by processor power dissipation can be probably regarded as a disadvantage, but it depends on your accuracy and resolution requirements. For very high accuracy (< 0.25K) it may be difficult to find a digital sensor with specified accuracy. Long-term stability seems to be a an unknown parameter for manufacturers of digital temperature sensors, as far as I have seen. (I would be glad to learn about different examples). As far as I know, for high accurate applications, analog Pt100 thermometers are still without competition (except for special designs as quartz crystal thermometers).

kender

Joined: 19 Jun 2005
Posts: 1231
Helped: 88
Location: Stanford, SF Bay Peninsula, California, Earth, Solar System, Milky Way

21 May 2008 17:42 temperature sensor zilog codes

McMurry wrote:

and respond to temperature changes more rapidly?

It depends on the construction of the sensor. An external temperature sensor could respond faster, if it has better conductivity and lower thermal mass. For example, the raise time of an LM75 which has a sensor inside SOIC should be comparable to the response time of a sensor internal to a microcontroller in SIOC. For example, thermocouple or LM35 in TO-220 package with exposed tab should have a faster response.

If you post the sensors and microcontrollers that you're considering and the driving factors for the temperature measurement, I would be happy to provide some more critique.

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rikie_rizza

Joined: 05 Aug 2006
Posts: 334
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Location: Bikini Bottom, between a rock and a pineapple

23 May 2008 10:13 what is the reading of failed temp sensor?

I recommend you to use external sensor for any type of precision temp reading. if it's only a simple reading (like reading ambient temp) than you won't need a high precision sensor...so you can use internal sensor from a device e.g. from micros, regulator, voltage comparator, etc.

Despite manufacturing characteristic and spec:
Digital sensors are dependent to its number of bits. Analog sensors are dependent to the performance the signal conditioning component. Well, mostly thou, still so many other factor to be consider for analog design.

McMurry

Joined: 16 Feb 2008
Posts: 75

26 May 2008 8:20 sensor need for reading

hi, thank you for all the replies.

i do not need such a high precision, cause it is only a small project i am working on to measure the temperature of an air space.

currently, i'm using ds18s20 (digital output). it is quite accurate.
but the other day, i heard once of my lecturer saying that analog temperature sensor actually gives a better reading. i'm not sure if its correct.

i had even try to interface lm35dz (very cheap!) temp sensor to Zilog mcu.. but failed to do the ADC conversion. i don't really understand how the ADC in the zilog mcu works.
the temperature reading output reading i obtained is not proportional to the changes in its output voltage i measured. sigh.

FvM

Joined: 22 Jan 2008
Posts: 5154
Helped: 766
Location: Bochum, Germany

26 May 2008 14:40 analogue temperature output for pic

From the specification, LM35 accuracy is clearly worse than DS18S20, on the other hand, as an analogue part it has a higher resolution, but depending on the scaling of it's output to ADC, it may not be utilized. To my opinion, for an easy and manufacturer calibrated measurement with medium resolution, digital sensors are preferable. You can get up to 1/16 K resolution with TI TMP275 (I2C interface).

rikie_rizza

Joined: 05 Aug 2006
Posts: 334
Helped: 20
Location: Bikini Bottom, between a rock and a pineapple

27 May 2008 3:02 adc temperature sensor sample projects

DS18S20 is a cheep excellent temp sensor. thou the res is only 0.5C, for air temp measurement is enough. Analog sensor do gives better reading with proper signal conditioning. but, if accuracy and resolution is not an issue, use digital instead.

Fragrance

Joined: 26 Jul 2002
Posts: 1385
Helped: 24

27 May 2008 5:23 disadvantage of tempreature sensor

McMurry wrote:

Hi

Lm35dz is good sensor for low cost application why not you used a pic micro with adc such as 16f676 or 16f88 or 16f877a in such case if you add more feature like high low setting and temp limmits then used 16f877 (if you need sample code i have some sample code written in pic basic plus

regards
Fragrance

McMurry

Joined: 16 Feb 2008
Posts: 75

29 May 2008 13:24 digital sensor calibration tmp275

FvM, rikie:

thank you. i have made my decision to use ds18s20.

Fragrance:

the zilog mcu that i am using has built-in adc as well, only that i have problem understanding the adc conversion thing. anyway, since im using a digital temp sensor, guess that would not be a problem any more =)

but when one problem is over, another problem arrive.

i have a friend who is doing a project titled "smart pc fan" that on/off at certain temp and i am aware that his project might downgrade my project.

here are what he did:
(a) he added LCD display module (which is exactly what i had added earlier)... sigh.
(b) he is displaying the temperature reading on LabView (while i'm displaying mine with Visual Basic). i'm not sure if he will log the temperature reading... probably he will too....

i've seen people using LabView and definitely, the GUI is much more attractive than Visual Basic. sigh.

i have planned to add a buzzer that will be turned on at certain temp, but it's not really that much impressive. is there any other good idea/application?

sigh. i hope my project will not be compared to his... but of course, if it is being compared, i wish mine is the better one.

seemanta

Joined: 10 Jun 2006
Posts: 71
Helped: 2

02 Jun 2008 15:16 ds1820 vs lm35

Even my experience with DS1820 has been generally good. Never tried any analog sensor though.

The advantage is clearly in terms of MCU pins. With DS1820, all you need is one pin.
You might even do away with the power supply in case you decide to use it with parasitic power supply.

With LM35, again you would need to do an A/D conversion and to get the digital data into your MCU, you would use up 8 data lines plus a few other A/D control lines (unless you decide to use some shift register which would again increase the complexity and power consumption of your device.)

DS1820, in my opinion is best suited for your work.

regards,
Seemanta

itachi012587

Joined: 09 Jun 2008
Posts: 24

10 Aug 2008 16:58 temperature sensor adc sample projects

Code:

Lm35dz is good sensor for low cost application why not you used a pic micro with adc such as 16f676 or 16f88 or 16f877a in such case if you add more feature like high low setting and temp limmits then used 16f877 (if you need sample code i have some sample code written in pic basic plus.

I need a sample code.

thank you.

McMurry

Joined: 16 Feb 2008
Posts: 75

12 Aug 2008 11:12 pic and lm75

i have sample code for LM35DZ interfaced to PIC. It is much easier than digital temperature sensor. PM me your e-mail. Very Happy

picsar

Joined: 06 Aug 2009
Posts: 9
Location: pakistan

09 Aug 2009 15:01 how to use lm35 to220 package

hello Mcmurry..can u please help me too with the same code??
i need to do the interfacing. Lm35 with pic. but also including the interfacing with ADC

sahu

Joined: 09 Oct 2009
Posts: 43
Helped: 3
Location: india

12 Oct 2009 17:11 Re: Need some opinions on temperature sensor

I HAVE 1 ASM FILE BASED 16F676 USING LM 35 SENSER.

Added after 32 minutes:

I HAVE 1 ASM FILE BASED 16F676 USING LM 35 SENSER

harrier3

Joined: 26 Oct 2009
Posts: 1

26 Oct 2009 16:14 Re: Need some opinions on temperature sensor

yg responnya paling cepet sensor apa?? ds1820 ato LM75 atto yg laen?? butuh referensi ney...

Aeddon

Joined: 05 Nov 2009
Posts: 5

21 Nov 2009 17:24 Re: disadvantage of tempreature sensor

Fragrance wrote:

McMurry wrote:

Hi Frangrance,
can you send me your sample of asm coding of temperature lm35dz in 16f877 best with buzzer and led showing high and low temperature alarm?
thanks