PIC and Thermocouple based homemade room temp monitor

[gl1]

Hi guys.
I want to monitor room temp of a room using thermocouple(not sure what type to use, i do not need too high of accuracy (+/- 0,5C)) and interface to PIC to record temp(not sure how to interface thermocouple to PIC)

Can some one please advise a type of thermocouple to use and post a circuit schematic.

The thermocouple will be at least 8m long and will wire up to PIC board 8m away.

Please help.

 

[KerimF]

Is it just for one board?

 

[ZASto]

Why you don't use DS18B20 digital temperature sensor? That way you will avoid analog part of the circuit. PURE DIGITAL :wink:

 

[gl1]

Yes i am thinling of using one PIC Board to monitor 3-4 zones/rooms.

Thanks for opinion Zasto, i will look at spec for DS18B20 - does it require any calibration?

---------- Post added at 20:48 ---------- Previous post was at 20:16 ----------

As i am thinking of project it is beginning to grow already.
I am thinking of also monitoring Humidity, any neat devices like DS18B20 to do both Temp/Humidity?

Also, Could i use DS18B20 to monior a Water Clyinder Temp? or would it be best to use a Thermocouple for this? and if so how should i interface Thermocouple to PIC?

Your contribution much appreciated.

 

[andre_luis]

gl1


This is not anymore usual to use thermocouple to measure enviromental temperature.
There exists much more precise IC based sensor solutions witch bocome pre-calibrated from manufacture ( despite is also possible to performs fine calibration at registers ).

However, thermocouple sensor is still an apropriate choice to operate in temperature range of houndreds of degrees ( > 300 oC ).

+++

 

[KerimF]

I think he looks for a temperature probe (based on an IC or else) that could be used in a wet place, better in water.

 

[andre_luis]

...will wire up to PIC board 8m away...

That´s another reason to adopt an IC based solution.

A thermocouple would need a special cabling ( twisted and/or shielded ) to avoid noise interference, and signal loses.
An IC can be used like a remote probe and communicate the measured value remotelly with no drop of information.

+++

 

[ZASto]

DS18x20 is declared to +/- 0.5 degrees C accuracy. If you can afford, you can contact an callibration lab to give you the certificate for your sensors, compared to the reference thermometer.

As per your wish to monitor the temperature in the water cylinder, thermocouples are NO/NO, you will have a water/liquid conductance interfering your thermocouple's uVoltage output.

For measuring temp/humidity, there are different type of digital sensors.

 

[gl1]

thanks for replys. Thermocouples are intended to only monitor on outside of cylinder-if possible.
I will do a search for some nice neat digital Temp/Humidity sensors.
But would still like to find some solution for connecting a thernocouple(K type maybe) to a PIC uC
Ta

 

[jenish]

the idea to interface temperature sensor to PIC is shown in attached figure.
it uses PT100 RTD and PIC 12c508 for better start

 

[ZASto]

With DS18x20 only two wires and one pullup resistor are needed

 

[Einar M]

Thermocouples may be cheap, but a circuit to convert the uV output to PIC is not. RTDs are made from platinum and cost like jewelry. A thermister would work here; it is pennies and interface is a pullup resistor to an AD input.