Newsgroups: comp.robotics
Path: brunix!sgiblab!spool.mu.edu!wupost!csus.edu!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: HELP: Simple A/D converter?
Message-ID: <nagleCD2r4w.Dz7@netcom.com>
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
References: <CD09zt.MK2@news2.cis.umn.edu> <111691@hydra.gatech.EDU>
Date: Thu, 9 Sep 1993 06:53:20 GMT
Lines: 34

jm59@prism.gatech.EDU (MILLS,JOHN M.) writes:
>In article <CD09zt.MK2@news2.cis.umn.edu> horton@molbio.cbs.umn.edu (Robert Horton) writes:
>>
>>Dear Hardware Hackin' Gurus of Netland;
>>I need to build/buy/get a board or (preferably) serial or (maybe even) 
>>parallel
>>device that will allow me to monitor a thermocouple with my PC. 

      A/D converter, 8 bit, 16 channel, RS-232 interface    $99.95
      Temperature input conversion, terminal block w/ 8 sensors,
	-40F to +145F					    $49.95

      Electronic Energy Control, Inc, 614-464-4470 for tech support.
      You can probably get a different temperature range if you need it.

There are many analog I/O boards for PCs.  This happens to be a cheap one.
I don't know if it is any good, but it's cheap.  

You could probably put a thermistor across a game port and get halfway
decent results.

Thermocouples are a pain to interface.  Thermocouples don't measure
temperature directly; they measure the difference between the hot
junction and the cold junction, so compensation is necessary if you
don't want room temperature to affect the output.  They also have
low output, so you need differential noise rejection.  And you have to
terminate the wires into special terminal blocks of the right kind of
metal, or you get a "reference junction" at the wrong place.  There are
good interfaces for thermocouples, and you can buy input cards for them.
It's a standard industrial item.  Once properly interfaced, thermocouples
are cheap and reliable.  See "The Art of Electronics", 2nd ed, p. 988-991 
for some circuits if you want to build.

						John Nagle
