ds2760 therocouple 28022

lightsout · 2005-03-20 01:43

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Alright I give up, I've been looking at this info that came with this (ds2760 thermocouple kit 28022) for hours today and I can't believe it's as complicated as it seems. I've searched google and the forum. I do see the unnecessary code in the beginning. But I'm not smart enough yet to understand the rest. Can someone give me a starting program, just enough to read a k-type t-couple and debug the temp. Something short and simple instead of the 5 pages they give you ?

T-couple kit: http://www.parallax.com/detail.asp?product_id=28022
Documentation: http://www.parallax.com/dl/docs/prod/compshop/DS2760.pdf

RickB · 2005-03-20 02:17

Have you loaded the program and data table into eeprom? Is it not working? Do you have a stamp with one wire commands?

Rick

lightsout · 2005-03-20 02:43

Rick,
I have a BS2p24 and no I have not programed/loaded anything as I am trying to integrate this T-couple into a already pretty full program. I have 2 of the BS2p24's on this project. One is 95% full (which I might be able to clean up) and another is 65% full. So therefore I don't think it is possible to add the 5 page "sample" program without greatly reducing it. And I can't do that because I don't understand most of the 5 page "sample". I just thought of something else,one of the stamps is about 3yrs old, I wonder if it will still do 1-wire ?
Thanks

RickB · 2005-03-20 07:36

The bsp24 does 1 wire. The code in the standard demo between main and declartions is not needed. Most everything else is needed. The debug statements in main can be removed and replaced with your own. Also, one of the 3 data lookup tables is necessary because the thermocouple output is nonlinear. If you don't need the full temperature range, you can delete the extremes you don't need. If I had a stamp with one wire commands I would have the thermocouple and could tell you more. What range of temps are you measuring?

Rick

lightsout · 2005-03-20 14:36

Rick,

The smallest temp range I would need would be about 200-800deg F and 25deg resolution would be ok. (50deg resolution if it meant having less code).

I did get this shorter code to work: http://www.parallax.com/dl/docs/prod/compshop/DS2760app.pdf

It gave incorrect results,(it does change temp when touching probe but shows 1800 at room temp), it still takes 56% eeprom memory and since I don't understand all of it, there's not too much of it I know to eliminate, (such as choice of probe and debug info). Can I load the temp probe code onto external eeprom? But then I still wonder how long it takes to go through the code, (take a temp reading), when I need it doing other things.

Soooo,it still comes down to needing very short code for a temp reading.

Thanks

P.S. the big gaps/spaces in my post were not by choice, it made me do it!

RickB · 2005-03-20 19:27

Do you have the N/V article that Jon wrote in Mar. 2004? You can download it from the download page at parallax. Thare is a very good explanation of the code that might allow you to shorten it more. With your limited resolution req. you can eliminate most of the lookup table for a huge savings in eeprom. The reading you provided appears to be the raw dc voltage that is used to index into the table. Have you loaded the table into eeprom? Since you dont req. much res. or accuracy you may be able to get away with a simple formula to arrive at the temp. However, a very short table (25 entries) might be easier. If you use an ext eeprom, you can load the entire table into it, but you will need to write code to access it . You can't run code in ext eeprom.
www.parallax.com/dl/docs/cols/nv/vol5/col/nv107.pdf

Rick

Tracy Allen · 2005-03-21 15:55

One-wire coding is kind of a pain. Another option would be the MAX6675 thermocouple conditioner chip for type K thermocouples. It is an SPI device and the coding is a lot simpler. It has the cold junction compensation built into the chip, so you don't have to do that in the software. No linearization, but your accuracy requirements are not so demanding.

' MAX6675
  LOW thcs      ' select chip
  SHIFTIN thdta,thclk,MSBPRE,[noparse][[/noparse]result\16]        ' get data
  HIGH thcs     ' end data capture
   THC=result>>3*/640      ' for MAX6675, degrees C*10
   DEBUG DEC THC/10, "degC" ,CR    ' 0 - 1023 degrees Celsius

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Tracy Allen
www.emesystems.com

lightsout · 2005-03-21 18:11

Thanks Tracy, thats sounds like something that will work for me !
I got my first free sample coming. Just when I was starting to feel good about my "self taught/online help" electronic abuilities,I came violently crashing down as I couldn't get that T-couple kit to work-for-nothing. I couldn't understand the code and even once I realized I needed the table, I still couldn't get it to go. The ds2760 thermocouple kit is definitly not for beginners !

ds2760 therocouple 28022

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