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'[PIC]: First pic project'
2002\08\19@125146 by Jan Malina

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Hi,

I read alot of posts on this list already, never really submitted anything
(mainly read the EE part though), and now I'm kinda interested in the PIC
microcontrolers. Now I haven't got any experience with them and I would
appreciate some help with my project.
I want to create a monitoring system for my watercooled PCs (2 PCs, one
loop). It should monitor a few temperatures (lets say... max of 8 temps),
use those to determine the voltage which should be fed to different fans
(about 2-3 fans), turn on/off the pumps (2) when required, and also handle
the powering of the PCs. While also dumping some statistics on a LCD (and
maybe keeping a small log of temps too). That shouldn't be too difficult,
but never having done anything with PICs I need some help selecting one... I
think I'll need quite a few I/O pins: quick calculation... 2 for the pcs (2
relays), 2 for the pumps (2 relays), 4 (?) pins for an LCD, 2-3 for the fans
(1 per fan?), dunno about the thermistors, I hope I don't need 1
pin/thermistor... Anyhow that would total at about 11-19 pins... Oh, I
missed a few buttons to interface with the thinggy (maybe go for a
keypad?)...

Thanks,

Jan

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2002\08\19@130846 by Tim Webb

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16F877 should have enough I/O pins


-----Original Message-----
From: Jan Malina [.....jan.malinaKILLspamspam@spam@PI.BE]
Sent: Wednesday, February 10, 1904 10:32 AM
To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subject: [PIC]: First pic project


Hi,

I read alot of posts on this list already, never really submitted anything
(mainly read the EE part though), and now I'm kinda interested in the PIC
microcontrolers. Now I haven't got any experience with them and I would
appreciate some help with my project.
I want to create a monitoring system for my watercooled PCs (2 PCs, one
loop). It should monitor a few temperatures (lets say... max of 8 temps),
use those to determine the voltage which should be fed to different fans
(about 2-3 fans), turn on/off the pumps (2) when required, and also handle
the powering of the PCs. While also dumping some statistics on a LCD (and
maybe keeping a small log of temps too). That shouldn't be too difficult,
but never having done anything with PICs I need some help selecting one... I
think I'll need quite a few I/O pins: quick calculation... 2 for the pcs (2
relays), 2 for the pumps (2 relays), 4 (?) pins for an LCD, 2-3 for the fans
(1 per fan?), dunno about the thermistors, I hope I don't need 1
pin/thermistor... Anyhow that would total at about 11-19 pins... Oh, I
missed a few buttons to interface with the thinggy (maybe go for a
keypad?)...

Thanks,

Jan

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2002\08\19@134656 by Olin Lathrop

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> 16F877 should have enough I/O pins

If he's new without any existing code base, I suggest starting with the 18F
series and never looking back.


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2002\08\19@134852 by Jan Malina

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Hmm i'm kinda lost, what would be an easy to use, simple programmer for the
16F877? (I'm running linux...)


Thanks,

Jan

op 19-08-2002 18:05 schreef Tim Webb op @spam@tim_webbKILLspamspamAGILENT.COM:

> 16F877 should have enough I/O pins
>
>
> {Original Message removed}

2002\08\19@135256 by Jan Malina

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>> 16F877 should have enough I/O pins
>
> If he's new without any existing code base, I suggest starting with the 18F
> series and never looking back.
>

Why do you recommend me to not mess with pre-18F chips?

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2002\08\19@135949 by Tim Webb

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That may also me a good idea...

-----Original Message-----
From: Olin Lathrop [RemoveMEolin_piclistTakeThisOuTspamEMBEDINC.COM]
Sent: Monday, August 19, 2002 10:46 AM
To: spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU
Subject: Re: [PIC]: First pic project


> 16F877 should have enough I/O pins

If he's new without any existing code base, I suggest starting with the 18F
series and never looking back.


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(978) 742-9014, http://www.embedinc.com

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2002\08\19@140210 by Herbert Graf

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> >> 16F877 should have enough I/O pins
> >
> > If he's new without any existing code base, I suggest starting
> with the 18F
> > series and never looking back.
> >
>
> Why do you recommend me to not mess with pre-18F chips?

       Because the 18F series solves alot of the "interesting" issues you would
have to learn about with the 16F's (and earlier). A very short list:
banking, the read write thing, and others. Also the 18F is the future. TTYL

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2002\08\19@145239 by Jan Malina

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>>>> 16F877 should have enough I/O pins
>>>
>>> If he's new without any existing code base, I suggest starting
>> with the 18F
>>> series and never looking back.
>>>
>>
>> Why do you recommend me to not mess with pre-18F chips?
>
> Because the 18F series solves alot of the "interesting" issues you would
> have to learn about with the 16F's (and earlier). A very short list:
> banking, the read write thing, and others. Also the 18F is the future. TTYL
>

If I'ld go with a 18F then, which one would you recommend, and could you
recommend a programmer too?

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2002\08\19@154044 by Wouter van Ooijen

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> If I'ld go with a 18F then, which one would you recommend,
> and could you recommend a programmer too?

1- get what is available
2- get what your wallet likes
3- if you still have a choice, take the largest (18f452)


of course I recommend my wisp628 kit ;)
http://www.voti.nl/wisp628

(By the time you have created a paypal account I will have 18f support
available)

Wouter van Ooijen

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2002\08\19@154050 by Wouter van Ooijen

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>         Because the 18F series solves alot of the
> "interesting" issues you would
> have to learn about with the 16F's (and earlier). A very short list:
> banking, the read write thing, and others. Also the 18F is

--^^^^^^^ misconception error

18f *does* use (register) banking. but it uses no (code) paging, just
limited-range braching.

Wouter van Ooijen

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2002\08\19@155946 by Brendan Moran

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> If I'd go with a 18F then, which one would you recommend, and could
> you recommend a programmer too?

The best I/O for cost etc... is, AFAIK the 18F452.  It has 8 A/D
lines.  You could get fancy and expand that to 16 via some analogue
switches, or you could implement an I2C (a serial bus protocol) A/D
chip.  As to the programmer, there aren't many 18F programmers at the
moment.

How much are you willing to spend as it stands?  Then we can give you
an answer as to which one would be good for you.

I suggest that instead of thermistors, you look at the LM35, which is
a linear temperature measurement device.  That means you have one
whole lot less calculations to do unless you want to use a simple
on/off system with no rate control for your fans and pumps, in which
case, linearity is irrelevant.

A good reference for finding datasheets is (And no I don't work for
them) http://www.chipcenter.com/questlink.  You have to sign up with them
but I haven't been spammed by them, so it's not too bad.

Regards,
- --Brendan

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2002\08\19@160359 by Brendan Moran

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> >         Because the 18F series solves alot of the
> > "interesting" issues you would
> > have to learn about with the 16F's (and earlier). A very short
> > list: banking, the read write thing, and others. Also the 18F is
>
> --^^^^^^^ misconception error
>
> 18f *does* use (register) banking. but it uses no (code) paging,
> just limited-range braching.

Thanks for pointing that out, Wouter.  I got a little burned by that
in a post last week. (:

The more often misconceptions are dispelled, the less often they
cause problems.

- --Brendan

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2002\08\19@160615 by Josh Koffman

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Jan,
In case you are unaware, I believe the clock on your computer/mailserver
is set wrong. Your posts are appearing to me as coming in
         Wed, 10 Feb 1904 21:32:07 +0100
Can anyone else substansiate this?

Josh

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A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
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Jan Malina wrote:
<snip>

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2002\08\19@160619 by Brendan Moran

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-----BEGIN PGP SIGNED MESSAGE-----
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> > If I'ld go with a 18F then, which one would you recommend,
> > and could you recommend a programmer too?
>
> 1- get what is available
> 2- get what your wallet likes
> 3- if you still have a choice, take the largest (18f452)
>
>
> of course I recommend my wisp628 kit ;)
> http://www.voti.nl/wisp628
>
> (By the time you have created a paypal account I will have 18f
> support available)

Well looky there, that would be the first programmer that I have
noticed supporting 18F parts.

Good job, Wouter!

- --Brendan

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2002\08\19@160621 by Olin Lathrop
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> Why do you recommend me to not mess with pre-18F chips?

The 18F chips are more capable and easier to program.  They costs slightly
more than the similar 16F chip in the same package in small quantities
(cheaper in large quantities), but that doesn't matter for hobby use if you
are only going to by 5 of them.  The 18F chips are also Microchip's "latest"
technology, so this is where the new development is.  I doubt you're ever
going to see a PIC16 with CAN or full speed USB, for example.


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2002\08\19@161903 by Jan Malina

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> Jan,
> In case you are unaware, I believe the clock on your computer/mailserver
> is set wrong. Your posts are appearing to me as coming in
> Wed, 10 Feb 1904 21:32:07 +0100
> Can anyone else substansiate this?
>
> Josh

Yea, i'm aware of that, just because my iBook somehow lost track of the time
somewere, I turned syncing with a timeserver back on, so that should be
fixed, i wonder how it got turned off anyhow.

Jan

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2002\08\19@162933 by Jan Malina

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>> If I'ld go with a 18F then, which one would you recommend,
>> and could you recommend a programmer too?
>
> 1- get what is available
> 2- get what your wallet likes
> 3- if you still have a choice, take the largest (18f452)
>
>
> of course I recommend my wisp628 kit ;)
> http://www.voti.nl/wisp628
>
> (By the time you have created a paypal account I will have 18f support
> available)
>
> Wouter van Ooijen

Hmm... I already have a paypal account :) And ordering my chips in the
netherlands would be pretty nice... or belgium, but then I have to find a
store selling them around here...

Jan

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2002\08\19@164007 by Mike Singer

picon face
part 1 1010 bytes content-type:text/plain; (decoded 7bit)

Olin Lathrop wrote:
> > Why do you recommend me to not mess with pre-18F chips?
>
> The 18F chips are more capable and easier to program.
> they costs slightly more than the similar 16F chip in
> the same package in small quantities (cheaper in large
> quantities), but that doesn't matter for hobby use if you
> are only going to by 5 of them.  The 18F chips are
> also Microchip's "latest" technology, so this is where
> the new development is.  I doubt you're ever going to
> see a PIC16 with CAN or full speed USB, for example.

In addition "PIC18CXXX Code Examples"(attached) from:

http://www.microchip.com/1000/suppdoc/appnote/codxamp/index.htm

Mike.

-----------------------------
PS:
I've lost:
1. "Language thing" to explain my faults.
2. "Communism" theme to bite somebody.
3. "18X vs 12-16X" theme to enjoy dissident feeling.
Etc.
Thanks very much. What should I do now? :-)




part 2 2399 bytes content-type:application/x-compressed; (decode)

part 3 105 bytes
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2002\08\19@164011 by Brendan Moran

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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

> Jan,
> In case you are unaware, I believe the clock on your
> computer/mailserver is set wrong. Your posts are appearing to me as
> coming in
>           Wed, 10 Feb 1904 21:32:07 +0100
> Can anyone else substansiate this?

Message-ID:  <35DD04.3645%spamBeGonejan.malinaspamKILLspampi.be>
Date:         Wed, 10 Feb 1904 20:33:09 +0100


- --Brendan

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2002\08\19@164014 by Olin Lathrop

face picon face
> If I'ld go with a 18F then, which one would you recommend,

For now there are two "hobby" 18F PICs.  The 18F252 if you want a 28 pin
package, and the 18F452 if you want a 40 pin package.  The 18F1320 isn't
real yet, but will be the hobby part for 18 pin packages.  For now if you
need an 18 pin package, use the 16F628.  However, unless you really really
need it to have only 18 pins, I wouldn't bother because programming it will
be different from the others.


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2002\08\19@164803 by Jan Malina

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op 19-08-2002 23:27 schreef Jan Malina op TakeThisOuTjan.malinaKILLspamspamspamPI.BE:

>>> If I'ld go with a 18F then, which one would you recommend,
>>> and could you recommend a programmer too?
>>
>> 1- get what is available
>> 2- get what your wallet likes
>> 3- if you still have a choice, take the largest (18f452)
>>
>>
>> of course I recommend my wisp628 kit ;)
>> http://www.voti.nl/wisp628
>>
>> (By the time you have created a paypal account I will have 18f support
>> available)
>>
>> Wouter van Ooijen

When will you have 18f support ready? Because your programmer seems really
clean & nice... (and free firmware updates and all)

Jan

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2002\08\19@165427 by Dale Botkin

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On Mon, 19 Aug 2002, Brendan Moran wrote:

> > of course I recommend my wisp628 kit ;)
> > http://www.voti.nl/wisp628

> Well looky there, that would be the first programmer that I have
> noticed supporting 18F parts.

EPIC+ (http://www.melabs.com) has for a while now.

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2002\08\19@165857 by Olin Lathrop

face picon face
Former Comrade Singer wrote:
> In addition "PIC18CXXX Code Examples"(attached) from:
>
> http://www.microchip.com/1000/suppdoc/appnote/codxamp/index.htm

I haven't looked at these, but beware that Microchip code samples may show
how to use their hardware, but usually exhibit very poor coding practises.

> I've lost:
> 1. "Language thing" to explain my faults.
> 2. "Communism" theme to bite somebody.
> 3. "18X vs 12-16X" theme to enjoy dissident feeling.

You could try starting a revolution.  The "worker's paradise" thing didn't
work out too well, so how about "aristrocrat's paradise" or "politician's
paradise".  No, wait we've already got that one.


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2002\08\19@170444 by Brendan Moran

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-----BEGIN PGP SIGNED MESSAGE-----
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> > > of course I recommend my wisp628 kit ;)
> > > http://www.voti.nl/wisp628
>
> > Well looky there, that would be the first programmer that I have
> > noticed supporting 18F parts.
>
> EPIC+ (http://www.melabs.com) has for a while now.

I did say "that I have noticed."  As in that someone said while I was
awake enough to absorb it (;

- --Brendan

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2002\08\19@171744 by Wouter van Ooijen

face picon face
> I did say "that I have noticed."  As in that someone said while I was
> awake enough to absorb it (;

What does the (; emoticon mean? A blinking chinese with a sun hat?

Wouter

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2002\08\19@171748 by Wouter van Ooijen

face picon face
> When will you have 18f support ready? Because your programmer
> seems really
> clean & nice... (and free firmware updates and all)

If you are willing to live with 'beta' software: now. But do specify on
your order that you want to use 18f's, because the firmware for the
16f628 is different.

Wouter

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2002\08\19@171755 by Wouter van Ooijen

face picon face
> > (By the time you have created a paypal account I will have
> 18f support
> > available)
> >
> > Wouter van Ooijen
>
> Hmm... I already have a paypal account :) And ordering my chips in the
> netherlands would be pretty nice... or bel

That matches, I have software that programs 18f's, but I would like to
add 16f87xA support before I put it on my web pages.

Wouter

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2002\08\19@174252 by Mike Mansheim

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> Well looky there, that would be the first programmer that I have
> noticed supporting 18F parts.

Just in case anyone is making a list, I've been programming 18F's
on Microchip's Promate II for a long time.

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2002\08\19@183135 by Richard Mellina

picon face
I had a real tough time getting a PayPal account too...
If that's what you mean.
Good luck!


>(By the time you have created a paypal account I will have 18f support
>available)

>Wouter van Ooijen

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2002\08\19@183748 by Bob Ammerman

picon face
For many 18F projects one can mainly ignore data banking, if you use a
certain memory allocation scheme:

1: Use the 'access' page to get access to low memory and SFR's

2: Set the BSR to point to a bank (say bank 1) and leave it there.

3: Use the remaining banks to store larger buffers, arrays, and perhaps a
data stack accessed via the FSR's.

Now you have immediate access to about 384 bytes of directly accessible
variables and simple access to the larger buffers via FSR.

Very simple to do.

Bob Ammerman
RAm Systems



{Original Message removed}

2002\08\19@192107 by Byron A Jeff

face picon face
On Mon, Aug 19, 2002 at 06:49:48PM +0100, Jan Malina wrote:
> Hmm i'm kinda lost, what would be an easy to use, simple programmer for the
> 16F877? (I'm running linux...)

If you are handy with wiring a board and can live without one I/O pin my
Trivial LVP Programmer is a good bet. You can find it here:

http://www.finitesite.com.d3jsys

With one chip and one resistor, usually you can get going quickly. Also I
have my version of picprg2.3d (soon to be 2.3e) which runs under Linux on
the page.

18F support is the next item on my list. Unlike Wouter it may be a month or
so before I get to it.

BAJ

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2002\08\19@193004 by hard Prosser

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Is that the correct url? - I'm  getting a "not found" error at the moment.
Richard P





On Mon, Aug 19, 2002 at 06:49:48PM +0100, Jan Malina wrote:
> Hmm i'm kinda lost, what would be an easy to use, simple programmer for
the
> 16F877? (I'm running linux...)

If you are handy with wiring a board and can live without one I/O pin my
Trivial LVP Programmer is a good bet. You can find it here:

http://www.finitesite.com.d3jsys

With one chip and one resistor, usually you can get going quickly. Also I
have my version of picprg2.3d (soon to be 2.3e) which runs under Linux on
the page.

18F support is the next item on my list. Unlike Wouter it may be a month or
so before I get to it.

BAJ

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2002\08\19@194437 by Barry Gershenfeld

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>Is that the correct url? - I'm  getting a "not found" error at the moment.
>Richard P

>http://www.finitesite.com.d3jsys

http://www.finitesite.com/d3jsys

"use the paste key, Luke!"

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2002\08\19@194452 by Rick C.

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The last dot should be a slash in the url
Rick

Richard Prosser wrote:

{Quote hidden}

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2002\08\19@200517 by Byron A Jeff

face picon face
On Tue, Aug 20, 2002 at 11:29:24AM +1200, Richard Prosser wrote:
> Is that the correct url? - I'm  getting a "not found" error at the moment.

Sorry. Typed too fast:

http://www.finitesite.com/d3jsys

{Quote hidden}

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2002\08\20@010621 by Bob Ammerman

picon face
Oh, and you can also use MOVFF to access any memory location in any bank in
two instruction words, eg:

   MOVFF    somereg,wreg


{Original Message removed}

2002\08\20@173911 by Jan Malina

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How would I handle the thermistors (i don't think i can use anything like a
LM35, as I need to read water temperatures, unless somebody knows how to use
a LM35 to read water temps...)?

Thanks,

Jan

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2002\08\20@180150 by Brendan Moran

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The problem is that in general, thermistors have a non-linear
Ohms/degree curve.  To handle that, you can either
a) accept non-linear response,
b) use hysteresis instead,
or c) go through the incredibly complex calculations to determine the
temperature from the resistance.

As to using the LM35 in a liquid measurement situation, I would go
for something like this:

1)Find a short (no more than a cm or two) piece of brass tubing that
is only slightly larger than the diameter of the curve of a TO-92
package.
2)Get some small silicone tubing that will fit over the brass tubing
3) Fill one end of the brass tubing with epoxy to create a seal
4)Insert something like heatsink grease , adding just enough that the
TO-92 package has a good thermal contact to the sides of the tubing.
5)Solder wires to the LM35, and heatshrink any bare metal
6)Slide the silicone tubing over the wires to the LM35
7)Insert the LM35 into the brass tubing witht he heatsink grease
8)Push the silicone tubing over the brass tubing, creating a seal,
but not going over the area occupied by the LM35
9)Now, install it anywhere that you want, within a cooling system.
You have a sealed temperature measurement device.  I wouldn't
recommend this for anything near food, though.

There's probably a simpler way of doing that, but that's what came
off the top of my head.

- --Brendan
- ---
"Rejection out of hand of all but one's favoured alternative may cost
you dearly in one way or another." -Russell McMahon



> How would I handle the thermistors (i don't think i can use
> anything like a LM35, as I need to read water temperatures, unless
> somebody knows how to use a LM35 to read water temps...)?

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2002\08\20@180420 by Scott Touchton

picon face
Dip the LM35 and the cable connections you make in conformal coat.
----- Original Message -----
From: Jan Malina <RemoveMEjan.malinaEraseMEspamKILLspamPI.BE>
To: <spamBeGonePICLISTspam_OUTspamRemoveMEMITVMA.MIT.EDU>
Sent: Tuesday, August 20, 2002 5:37 PM
Subject: Re: [PIC]: First pic project


> How would I handle the thermistors (i don't think i can use anything like
a
> LM35, as I need to read water temperatures, unless somebody knows how to
use
{Quote hidden}

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2002\08\20@181739 by Jan Malina

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face
> The problem is that in general, thermistors have a non-linear
> Ohms/degree curve.  To handle that, you can either
> a) accept non-linear response,
> b) use hysteresis instead,
> or c) go through the incredibly complex calculations to determine the
> temperature from the resistance.

I know, that's why I'm asking about the LM35

{Quote hidden}

That isn't a really bad idea, but I don't think I can fit that in the tubes
without seriously restricting flow... maybe I could do it with a smaller
SO-8 or TO-46 package... or maybe bolting a TO-220 to a small metal strip
(copper), of cource isolated, and inserting the metal strip into the water,
that is the first thing that popped in my head.
Or maybe there is a much easier, better way and somebody wants to enlighten
me with his knowledge/experience (tubing size varies between 3/8" and 3/4"
OD) :)

Jan

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2002\08\20@182948 by Brendan Moran

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> That isn't a really bad idea, but I don't think I can fit that in
> the tubes without seriously restricting flow... maybe I could do it
> with a smaller SO-8 or TO-46 package... or maybe bolting a TO-220
> to a small metal strip (copper), of cource isolated, and inserting
> the metal strip into the water, that is the first thing that popped
> in my head.
> Or maybe there is a much easier, better way and somebody wants to
> enlighten me with his knowledge/experience (tubing size varies
> between 3/8" and 3/4" OD) :)

Thermally epoxy one onto the outside of a piece of copper tubing?

Maybe we should take this over to [EE]: now?

- --Brendan
- ---
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you dearly in one way or another." -Russell McMahon

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2002\08\21@005550 by Nelson Hochberg

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Use a TO-92 package for the LM35 and pot it after attaching the wires.  If
used in food, you can use a food grade potting compound.

Nelson

{Original Message removed}

2002\08\21@031943 by Michael Rigby-Jones

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> -----Original Message-----
> From: Bob Ammerman [SMTP:.....rammermanspamRemoveMEADELPHIA.NET]
> Sent: Tuesday, August 20, 2002 4:57 AM
> To:   PICLISTspam@spam@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: First pic project
>
> Oh, and you can also use MOVFF to access any memory location in any bank
> in
> two instruction words, eg:
>
>     MOVFF    somereg,wreg
>
With a few exceptions! PCL, TOSU, TOSH, TOSL cannot be the destination.
Very usefull instruction though.

Regards

Mike

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2002\08\21@043237 by Alan B. Pearce

face picon face
> or c) go through the incredibly complex calculations to determine the
> temperature from the resistance.

This depends on how accurate you need the temperature. Unless you are
operating at extreme temperatures, you can probably linearise the sensor
enough using a pre-calculated table read, especially if your temperature
range is within what an LM35 will handle.

Use something like Excel to generate the table, and if you do it correctly,
Excel can be persuaded to generate the table source code for you.

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2002\08\21@043258 by Quentin

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> The problem is that in general, thermistors have a non-linear
> Ohms/degree curve.  To handle that, you can either
> a) accept non-linear response,
> b) use hysteresis instead,
> or c) go through the incredibly complex calculations to determine the
> temperature from the resistance.
Jumping in here..
If you need to use a temp. probe, you can also use a thermo couple with an
AD594 from Analog Products.

Quentin
EraseMEqscRemoveMEspamSTOPspamiptech.co.za
http://www.iptech.co.za

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2002\08\21@060413 by Michael Rigby-Jones

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> -----Original Message-----
> From: Brendan Moran [SMTP:RemoveMEbmoranKILLspamspamTakeThisOuTMILLENNIUM.CA]
> Sent: Tuesday, August 20, 2002 11:01 PM
> To:   spamBeGonePICLISTspam@spam@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: First pic project
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> The problem is that in general, thermistors have a non-linear
> Ohms/degree curve.  To handle that, you can either
> a) accept non-linear response,
> b) use hysteresis instead,
> or c) go through the incredibly complex calculations to determine the
> temperature from the resistance.
>
Or d) use a simple lookup table with interpolation to get excellent (<0.1C)
accuracy.

Regards

Mike

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2002\08\21@093231 by Olin Lathrop

face picon face
> or c) go through the incredibly complex calculations to determine the
> temperature from the resistance.

You generally don't need "incredibly complex" calculations.  The true
thermistor equation derived from the physics is rather complex, but it can
be modeled to arbitrary accuracy with simpler equations, like polynomials
for example.  It depends on the temperature range and desired accuracy, but
a third order polynomial might be good enough.  That's only 5 multiplies and
3 adds.  Add 2 multiplies and 1 add per polynomial order, so a 5th order
polynomial is 9 multiplies and 5 adds.  A haven't worked it out, but I
rather suspect that a 5th order polynomial will be better than other sources
of error in the system.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\08\21@105416 by Spehro Pefhany

picon face
At 09:31 AM 8/21/02 -0400, you wrote:


>You generally don't need "incredibly complex" calculations.  The true
>thermistor equation derived from the physics is rather complex, but it can
>be modeled to arbitrary accuracy with simpler equations, like polynomials
>for example.  It depends on the temperature range and desired accuracy, but
>a third order polynomial might be good enough.  That's only 5 multiplies and
>3 adds.  Add 2 multiplies and 1 add per polynomial order, so a 5th order
>polynomial is 9 multiplies and 5 adds.  A haven't worked it out, but I
>rather suspect that a 5th order polynomial will be better than other sources
>of error in the system.

Over a halfway wide temperature range, polynomials are quite ill-suited for
this purpose. I've tried it up to about 9th order. It may well be possible
to do a couple of operations first to make the equation more suitable for
polynomial approximation.

Your suggestion of low-order polynomials would probably work if the range
was split up into segments, along the lines of classic spline interpolation
algorithms.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffspam_OUTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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2002\08\21@115434 by Dave Tweed

face
flavicon
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Olin Lathrop <olin_piclistspamspamEMBEDINC.COM> wrote:
> ... It depends on the temperature range and desired accuracy, but a third
> order polynomial might be good enough.  That's only 5 multiplies and 3
> adds.  Add 2 multiplies and 1 add per polynomial order, so a 5th order
> polynomial is 9 multiplies and 5 adds.  A haven't worked it out, but I
> rather suspect that a 5th order polynomial will be better than other
> sources of error in the system.

A simple transformation allows polynomials to be evaluated with one
multiply and one add per order:

  A*x^3 + B*x^2 + C*x + D =
     (((A*x + B)*x + C)*x + D)

-- Dave Tweed

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2002\08\21@150912 by Jan Malina

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Hmm, I looked at Maxim their temperature sensors, and the DS1631 looks
pretty nice: small package & I2C interface. The I2C interface might be
really handy for this project, otherwise I'll just end up eating pins :/
Guess I can easily attach an EEPROM I2C chip for temperature logging too
then...

Also, a few other problems, I'ld like to adjust the voltage of some fans
with the PIC, how would I easily do that? Wire the PIC to a digital
potentiometer which adjusts the ADJ voltage of a small linear regulator
(like the LM138)?

Hmm, I also think I should pick up some kind of book about electronics as my
knowledge is uhm... pretty limited. "The Art Of Electronics" looks like a
nice book, any recommendations?

Jan

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2002\08\21@151902 by Brendan Moran

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> Hmm, I looked at Maxim their temperature sensors, and the DS1631
> looks pretty nice: small package & I2C interface. The I2C interface
> might be really handy for this project, otherwise I'll just end up
> eating pins :/ Guess I can easily attach an EEPROM I2C chip for
> temperature logging too then...

Uh... you may have some troubles here.  I2C operates on addresses.
How many programmable addresses does that I2C temperature sensor
have?  This could be a problem for you.

> Also, a few other problems, I'ld like to adjust the voltage of some
> fans with the PIC, how would I easily do that? Wire the PIC to a
> digital potentiometer which adjusts the ADJ voltage of a small
> linear regulator (like the LM138)?

I would recommend using a multi-channel D/A converter with an I2C
interface.  Use that as the adj pin's input on hmm...

I assume 12V fans, right?  Then 12-5=> 7V.  Closest that's higher is
9V.

Use it as the input to a 9V regulator's adj pin.  This will give you
a voltage range from 9-14V (be careful not to go above 12V)

- --Brendan

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2002\08\21@152554 by Tom Messenger

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At 09:08 PM 8/21/02 +0200, you wrote:
>
>Hmm, I also think I should pick up some kind of book about electronics as my
>knowledge is uhm... pretty limited. "The Art Of Electronics" looks like a
>nice book, any recommendations?
>
>Jan


"The Art Of Electronics" is indeed a good all around book.  It will get you
far enough along to understand circuit design or at least know what
questions to ask.

Tom M.

ps: note to Aaron T.: get yourself a copy! And throw out those bad
transistors:)

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2002\08\21@160300 by Jan Malina

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>> Hmm, I looked at Maxim their temperature sensors, and the DS1631
>> looks pretty nice: small package & I2C interface. The I2C interface
>> might be really handy for this project, otherwise I'll just end up
>> eating pins :/ Guess I can easily attach an EEPROM I2C chip for
>> temperature logging too then...
>
> Uh... you may have some troubles here.  I2C operates on addresses.
> How many programmable addresses does that I2C temperature sensor
> have?  This could be a problem for you.

Lemme check the datasheet... the lower 3 bits of the address are user
selectable, so I can drop 8 of them on one bus... hmm... should be OK I
think. Maybe there are some other sensors like this with more bits user
selectable, dunno...

{Quote hidden}

Actualy I would prefer a 5-12V range, as most of the fans i'm using have no
problems starting at 5V (they are nice & quiet then...), and I would prefer
not to overvolt fans... actualy you just lost me somewhere... hmm... why did
you substract 5v from 12?
And, just an idea, would it be possible to use a multichan a/d convertor for
the termistors? just to save some pins/addresses?

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2002\08\21@174447 by Brendan Moran

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source= http://www.piclist.com/postbot.asp?id=piclist\2002\08\21\160300a



Actualy I would prefer a 5-12V range, as most of the fans i'm using
have no
problems starting at 5V (they are nice & quiet then...), and I would
prefer
not to overvolt fans... actualy you just lost me somewhere... hmm...
why did
you substract 5v from 12?
And, just an idea, would it be possible to use a multichan a/d
convertor for
the termistors? just to save some pins/addresses?

Ok, I said 12v-5V so that you'd be using a 0-5V d/a converter.

On sober second thought, that's really unnecessary.  Use a 15V
supply, and bias your D/A in software so that it doesn't get too
high.  Try using an LM317, since it only rises 1.2V above its adj
pin.

As to the multichannel A/D converter, most PICs have A/D converters
built in, but if you need more A/D channels, that's the way to go.
If you want to use thermistors, I suggest going with the suggestion
of using a lookup table.  I like the thought of using a current
output temperature sensor, with a 10k resistor.  You still need the
A/D, but you only run 2 wires instead of 4.

---
Brendan
PIC/PICList FAQ: http://www.piclist.com

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2002\08\21@175303 by Jan Malina

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> As to the multichannel A/D converter, most PICs have A/D converters
> built in, but if you need more A/D channels, that's the way to go.
> If you want to use thermistors, I suggest going with the suggestion
> of using a lookup table.  I like the thought of using a current
> output temperature sensor, with a 10k resistor.  You still need the
> A/D, but you only run 2 wires instead of 4.

Hmm... 2 wires per temperature sensor :/ I think i'll look some more into
I2C temperature sensors... unless you can give me a good reason to not use
them? As I still need a few spare pins for a few relays, lcd (unless i can
get that on I2C too...) and a couple of buttons/keypad... still don't really
know if I should go with a 40 or 28 pin PIC...

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2002\08\21@182400 by Brendan Moran

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> Hmm... 2 wires per temperature sensor :/ I think i'll look some
> more into I2C temperature sensors... unless you can give me a good
> reason to not use them? As I still need a few spare pins for a few
> relays, lcd (unless i can get that on I2C too...) and a couple of
> buttons/keypad... still don't really know if I should go with a 40
> or 28 pin PIC...

Here, let me outline two possibilities for a system:

I'm going to assume 12 temp sensors, 12 controlled devices for this
example, you can scale that to what ever you want.

1)
Output:
12 I/O lines from the PIC go to NPN transistors, which drive relays
for the fans and pumps, unless the current requirement is under
100mA, in chich case, the transistor itself drives the devices.
Software PWM is used to control the voltages on the fans and pumps.
Input:
All 8 A/D lines are used for reading 8 current based temp sensors.
The PIC takes its analog input between the temp sensor and a 10K
resistor.  This takes only 1 PIC pin per sensor.
I2C is used to interface to a 4 channel A/D converter for the
remaining 4 temp sensors

2)
Output:
Several I2C DACs are used to interface to small power transistors,
which feed the required current to the fans and pumps at 0.7V less
than the DAC output.
Input:
SMBus temperature sensors are fed through an I2C hub to allow for
more than 8 of them, and to convert the SMBus voltage levels to I2C
levels. Each temperature sensor requires a connection to +5V, 0V,
SCL, and SDA.  Several PIC control pins are used to change the
selected channel, thereby preventing bus contention.

Conclusions:
Mix this up as much as you want.  Remember that with I2C, you have to
be careful about bus capacitance.  You may need to use special I2C
trancievers to handle any long runs.

My recommendation?  Use the input from 1) and the output from 2)

Here's what I'd do:  Use some kind of analogue output temperature
sensor, and connect it however you were going to, then read those
ouputs with I2C A/D converters.  From those outputs, calculate what
you need to, then run the outputs to I2C D/A converters, which run
their ouptuts into power transistors.  Connect the power transistors
thusly:  Base to DAC collector to 15V(12V maybe), emitter to
fan/pump.

And you still have all your PIC inputs left except for the 2 for the
I2C interface.  With that, you can use a small PIC, just as long as
it supports I2C.  Though, you *could* use software based I2C on a
smaller PIC, but it's a bit trickier.  But you said you were thinking
of an 18F PIC, I think, and I think that most of them support I2C.

Another protocol to consider is SPI.

- --Brendan

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2002\08\22@022206 by Michael Rigby-Jones

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       -----Original Message-----
       From:   Spehro Pefhany [SMTP:spam_OUTspeffspam_OUTspamspam_OUTINTERLOG.COM]
       Sent:   Wednesday, August 21, 2002 4:06 PM
       To:     PICLISTspam_OUTspamMITVMA.MIT.EDU
       Subject:        Re: [PIC]: First pic project

       At 09:31 AM 8/21/02 -0400, you wrote:


{Quote hidden}

Forming a potential divider with a resistor value equal to the thermistor
resistance in the middle of the desired range has a linearising effect.
Combined with a table and simple first order interpolation this can yield
surprisngly good results, but again over a limited temperature range.
Towards the temperature extremes the non-linearity becomes progresively
worse, and the slope reduces to the point that you start losing a lot of
resolution.  Then again, thermistors are generaly only used for relatively
narrow temperature ranges or for cheap and cheerfull non-precision
applications.

Regards

Mike

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2002\08\22@072209 by Jan Malina

flavicon
face
> Here, let me outline two possibilities for a system:
>
> I'm going to assume 12 temp sensors, 12 controlled devices for this
> example, you can scale that to what ever you want.
>
> 1)
> Output:
> 12 I/O lines from the PIC go to NPN transistors, which drive relays
> for the fans and pumps, unless the current requirement is under
> 100mA, in chich case, the transistor itself drives the devices.
> Software PWM is used to control the voltages on the fans and pumps.

100mA for a fan or pump is a bit optimistic i think :D
Would the NPN transistors also work for AC pumps? (don't think so)
Hmm, maybe i should check if the pumps i plan to use are AC or DC...

{Quote hidden}

I don't think there are going to be any really long runs... the distances
will be pretty short (haven't really measured yet) :)

> My recommendation?  Use the input from 1) and the output from 2)

> Here's what I'd do:  Use some kind of analogue output temperature
> sensor, and connect it however you were going to, then read those
> ouputs with I2C A/D converters.  From those outputs, calculate what
> you need to, then run the outputs to I2C D/A converters, which run
> their ouptuts into power transistors.  Connect the power transistors
> thusly:  Base to DAC collector to 15V(12V maybe), emitter to
> fan/pump.

Hmm, yea, that looks like the easiest... And with multichannel A/D and D/A
chips this should be pretty easy & clean. And if I would use thermistors,
then I could keep the I2C bus pretty short to avoid problems (although
longer wires to the thermistors will give a worse accuracy afaik).

> And you still have all your PIC inputs left except for the 2 for the
> I2C interface.  With that, you can use a small PIC, just as long as
> it supports I2C.  Though, you *could* use software based I2C on a
> smaller PIC, but it's a bit trickier.  But you said you were thinking
> of an 18F PIC, I think, and I think that most of them support I2C.

Yea, I basicly wanted to save a few pins so that I have some spare ones for
some buttons/a keypad and a LCD... Now I still have to find a nice, small,
18F PIC (28 pin DIP or something like that was what I originaly wanted to
use...)

> Another protocol to consider is SPI.

Hmm, i don't really know that much about I2C (just the basic theory, haven't
actualy used it yet), but i know even less about SPI, IIRC it's a 3 wire
interface...

Going to think it over one more time, select the components to use, find me
a decent PIC programmer (which i can use from linux... Wouter's programmer
looks nice, maybe I should ask him if i'm allowed to port his software to
linux) and lets get busy! Be sure to expect me back with some more
questions/problems soon :)

Thanks, you (and others on this list of course) have been very helpful :)

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2002\08\22@080855 by Jan Malina

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Quickly browsed through microchips's website and i think the 18F242 or
18F252 would be perfect...

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2002\08\22@131030 by Olin Lathrop

face picon face
> Quickly browsed through microchips's website and i think the 18F242 or
> 18F252 would be perfect...

For hobby use I would not get the 18F242.  It is the same as the 252 except
it has less program and data memory.  The slight cost savings can be
meaningful in production quantities, but is not worth the loss in
flexibility when you are only buying 5 of them.


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2002\08\22@132606 by Jan Malina

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face
>> Quickly browsed through microchips's website and i think the 18F242 or
>> 18F252 would be perfect...
>
> For hobby use I would not get the 18F242.  It is the same as the 252 except
> it has less program and data memory.  The slight cost savings can be
> meaningful in production quantities, but is not worth the loss in
> flexibility when you are only buying 5 of them.

Hmm yea, you're right. And a 28 pin one would be the best for most hobby use
anyhow (maybe i'll build another system like i'm planning to sell, but no
production quantities).

Jan

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2002\08\23@083137 by Alan B. Pearce

face picon face
Hold those temperature sensors :)

A new Maxim brochure just across my desk lists a new temperature sensor from
Dallas/Maxim, the DS18B20 +/-0.5C accurate over -10 to +85 range (also
available as +/-2C as a DS1822) with user configurable from 9 to 12 bits
resolution. Uses the 1-wire bus system.

Other interesting devices are the MAX6674/5 which is a direct thermocouple
to digital converter in 8 pin SO package, integrated cold junction
compensation, 10/12 bit word, and SPI interface.

MAX6682/6691 thermistor to digital which minimises the thermistor
dissipation by only having current through it when needing to do the
measurement. 10 bit, SPI interface, 6682 handles single thermistor, 6691
handles 4 thermistors.

Various other as well, including an LM75 replacement (DS1775) in a 5 pin
SOT23 package.

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2002\08\23@122131 by Jan Malina

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> Hold those temperature sensors :)
>
> A new Maxim brochure just across my desk lists a new temperature sensor from
> Dallas/Maxim, the DS18B20 +/-0.5C accurate over -10 to +85 range (also
> available as +/-2C as a DS1822) with user configurable from 9 to 12 bits
> resolution. Uses the 1-wire bus system.

Guess I'll get that brochure soon too :)

> Other interesting devices are the MAX6674/5 which is a direct thermocouple
> to digital converter in 8 pin SO package, integrated cold junction
> compensation, 10/12 bit word, and SPI interface.
>
> MAX6682/6691 thermistor to digital which minimises the thermistor
> dissipation by only having current through it when needing to do the
> measurement. 10 bit, SPI interface, 6682 handles single thermistor, 6691
> handles 4 thermistors.

That looks mighty interesting... would be nice to have that on a I2C
interface though, i'll check their site to see if they have something
similar with I2C.

> Various other as well, including an LM75 replacement (DS1775) in a 5 pin
> SOT23 package.

:)

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2002\08\23@123352 by Alan B. Pearce

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>That looks mighty interesting... would be nice to have that on a I2C
>interface though, i'll check their site to see if they have something
>similar with I2C.

Yeah well there is so much in the monthly doings that I just glance through
it. The DS1775 (LM35 equiv) is listed as SMBus, which should run on an I2C.

A number of other devices are listed as SMBus, MAX6680/1 and MAX6660 which
are both designed as CPU temperature sensors with transistor on chip sensor.

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