Thermometer with PIC-->Help me please!

[Pappee]

Hi All!

I wold like to build a micro-controller based thermometer. I have searched a lot on the net, but i didn't found a thermometer, what is good for me. I don't want simple see the temp.,I would like to controll it(for heating). I have think for PIC 16F628... :roll:
If someone could help me, please write me.

Special thanks!

 

[Jay.slovak]

Hi All!

I wold like to build a micro-controller based thermometer. I have searched a lot on the net, but i didn't found a thermometer, what is good for me. I don't want simple see the temp.,I would like to controll it(for heating). I have think for PIC 16F628... :roll:
If someone could help me, please write me.

Special thanks!

16F628 is a good choice. I did a similar project just recently, where I used 18F1320, DS18S20 (Dallas 1wire calibrated thermometer) and LED display. It was easy. Temperature controlling will be done via PWM module and no calibration will be needed thanks to DS18S20.

 

[Oznog]

There are 4 possibilities:
1. Temp sensor- these cheap devices are already linear. Downside is they have a limited temp range (usually can't sense less than freezing).
2. Thermistor- cheap, very large temp range. Downside, nonlinear and requires a lookup table inside the PIC.
3. Thermocouple- can measure very high temps. It's just 2 pieces of cheap thermocouple wire tied together. Downside, very low voltage and thus requires a special amplifier or ADC to handle it. Thermocouples actually only sense temp differences, not an absolute temp. So if the side of the wire attached to PIC is 10F hotter, the reading will go down 10F between it and a hotter object.
4. Digital temp sensor, like the DS18S20. The DS18S20 is relatively expensive compared to thermistors or temp sensors but still only a few bucks. Downside is the 1-wire protocol can be just a little bit difficult to use with systems that use interrupts.

 

[Pappee]

Nice

Nice work Jay.slovak & Oznog!

But please give me a LINK please !

 

[Oznog]

What exactly do you want to use this for?? This will change the answer.

 

[Jay.slovak]

If you like my solution with DS18S20, check its datasheet out : **broken link removed**

 

[eblc1388]

LM35, -40 to 100 degree C. Accuracy within 1 degree. Linear output. Price less than one US$. But it only gives you a voltage proportional to temperature.

**broken link removed**

The DS chip gives you the actual temperature data in serial format so no other format conversion needed.

 

[Pappee]

Thermometer

I would like to control heating of a room.That's why i need a PIC based schematic what contol a relay.So,can U help me?

Thanx!

 

[Oznog]

LM35, -40 to 100 degree C. Accuracy within 1 degree. Linear output. Price less than one US$. But it only gives you a voltage proportional to temperature.

It's not capable of temp readings below 2C unless you have a negative supply. All sensors of this type seem to have this liability.

Accuracy of 1 deg C is a bit poor for room temp sensing, not too bad though. That's 1.8 deg F. I find a lot of difference between having the room at 70F and 68F. Also the output is 10mV/degC so offset error in the PIC may be significant, several degrees even. Calibration can fix some of these problems, the PIC offset might be a bit troublesome though.

DS18S20 is a good part, I like it. At something like $3-$4 it's a bit high for a basic component but it is good.

I think thermistors are the most common sensor in home thermostats. I could be wrong though. Most thermistors are a bit more on the inaccurate side unless calibrated, I was curious and a 5% thermistor would be +/- 5.6 deg F by my calculations.

 

[Beefer3]

Actually, thermistors are very accurate by themselves in the range of 0C to 70C. Most manufacturers state taht the interchangability error is in the range of 0.1C to 0.2C.

You must be careful of the the term "calibration". Calibration is adjusting a device to a known standard. Since thermistors are resistive elements, they do not lend themselves to actual adjustments. You can however, create a table of temperature points and create code to lookup the table.

 

[garg29]

just now i've replied to this kind of question chekout this link
https://www.electro-tech-online.com/threads/two-hardware-usarts.18792/

 

[hantto]

**broken link removed**

8-pin, 125°C to -55°C sensing, I²C-bus (2wire), result in two registers (one if you only need one degrees resolutuion) A good temperature sensor, even with a thermostat pin, so you can actually just configure the chip once and then run stand-alone.

 

[georges]

hi all
im building a pic16F877A based thermometer and im using a thermistor as a sensor ! the result will display on a LCD 2*16 !
im wondering if someone can help to write a source code(mikrobasic) cause im having difficulties to display all 4 digits on LCD ( 25.20 celsius for example )
thank u all

 

[ericgibbs]

hi all
im building a pic16F877A based thermometer and im using a thermistor as a sensor ! the result will display on a LCD 2*16 !
im wondering if someone can help to write a source code(mikrobasic) cause im having difficulties to display all 4 digits on LCD ( 25.20 celsius for example )
thank u all

hi,
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It would best to start a new thread.