Thermocouple to PC

[GatorGnet]

I need to build a simple control board to take a reading from a thermocouple and send it to a PCs serial port.(usb would be even better but serial should be easier)

I have found some really expensive control boxes online however as with all of us on here I feel that I hope to build one cheaper.

The temps will range from 0-2200F if it makes a difference. Also, I need to be able to send out signals on the same serial port connects.

Any ideas would help at this point.

 

[Vizier87]

Okay... for the UBW guys.. here I am posting it first!! )
See this page: UBW (USB Bit Whacker) Project
it describes communication between PICs which takes in the analog data from it to PC.

 

[vne147]

Okay... for the UBW guys.. here I am posting it first!! )
See this page: UBW (USB Bit Whacker) Project
it describes communication between PICs which takes in the analog data from it to PC.

Cool link Vizier. I'm going to have to build that now.

 

[Nigel Goodwin]

Cool link Vizier. I'm going to have to build that now.

It makes life easy, and is a great solution for modern PC's that don't have serial or parallel ports.

 

[Reloadron]

I see 0 to 2,200 Degrees F. so shall I assume a furnace application with a standard Type K thermocouple? Also is this an industrial application (commercial)? In the event of a thermocouple failure like open TC would you want an upscale or downscale indication? Do you just want to see a displayed temperature or actually record the temperatures?

Personally I would likely go with a programmable temperature transmitter and run the output into a PIC. How you read the PIC on the PC has been already mentioned.

Ron

 

[GatorGnet]

I'm in a hurry so I will answer more questions when I get off work but yes it is for a kiln operation. Recording is not an issue because I am going to build a software package that will handle that. It will be for commercial needs but light(er) duty. And yes, a K type thermocouple. I'll check out the USB interface when I get home.

So far I just need the thermocouple to send the temp to a PIC and I can send it out to the PC from there.

 

[Reloadron]

If you want to keep it simple and design your own circuit you could probably buils around the Analog Devices AD594 or AD595 chips. This data sheet pretty much covers things and the chips do have CJC (Cold Junction Compensation). Depending on the variation of the chip you use I think about between $20 & $30 USD for the chip. The chip outputs 10 mV Deg C and the link covers doing the math for different TC types including K. You would need to add further amplification but it would get you there.

Another option is just to buy an off the shelf TT (Temperature Transmitter) that will output a span of 4 to 20 mA for a preset temperature range and type TC. I use Inor types and generally the IPAQ-H variety. They are easy to program for temperature range and TC type and also beyond CJC offer burnoput upscale or downscale output. I think we pay about $70 USD for those units give or take. There are circuits **broken link removed** to convert a 4-20 loop to 0 to 5 Volts or if you cheat a little just place a good precision 250Ω resistor in the loop and get 1 to 5 Volts.

When using a TC and controller to control a furnace or kiln you want over temp protection of some sort.

Anyway, just a few thoughts on the subject.

Ron