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'Comments and questions about DS1820'
2000\01\31@041101 by Rod Phillips

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Hello to all,

I am using a DS1820 to measure outdoor temperature, and get a large
difference when supplying 5v to the device as opposed to operating on
parasite power.  Without the 5v the temperature reading is about 5 degrees
(F) lower - this morning 3 above with 5v and 2 below without it.  I am using
about 60 feet of Cat. 5 cable. The reading with 5v connected is the correct
reading.  Any ideas?

Along the same line I am now wanting to add more 1820s to the system but
have hit a snag.  I read the 64 bit serial number from several devices and
put  a "Match Rom (55h)" command in the program to select the chip I want to
read.  The problem is that the micro doesn't always read the addressed
device when there is another 1820 on the line.  I have a couple of 1820s
that will work together but others, including my outside device, won't work
at all with a second device on line.  All devices work fine by themselves
even though they still must match the serial number.

Any ideas?


Rod

2000\01\31@073605 by Peter Keller

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Rod Phillips schrieb:

> Hello to all,
>
> I am using a DS1820 to measure outdoor temperature, and get a large
> difference when supplying 5v to the device as opposed to operating on
> parasite power.  Without the 5v the temperature reading is about 5 degrees
> (F) lower - this morning 3 above with 5v and 2 below without it.  I am using
> about 60 feet of Cat. 5 cable. The reading with 5v connected is the correct
> reading.  Any ideas?
>

I had the same problem on a Cat.5 cable of 100 feet length.
My solution was:
Supply +24V over the cable and have a 5V Lin.Regulator at the end where the
sensor is.
Peter

{Quote hidden}

No, but I am interested.

>
>
> Rod


'Comments and questions about DS1820'
2000\02\01@020807 by Ruben Jšnsson
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In EDN (europe) march 1999 (http://www.ednmag.com) there is a design idea
called 'Simple circuit prevents processor latch-up' which is an
interface circuit for DS1820's. Besides preventing processor latch-up
the circuit also conditions the signals via active pullupp. However,
it uses two I/O's instead of one. I have not tried this myself (yet)
but it may be worth checking out.

{Quote hidden}

==============================
Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
spam_OUTrubenTakeThisOuTspampp.sbbs.se
==============================

2000\02\02@045351 by Rod Phillips

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----- Original Message -----
From: Peter Keller <.....pkellerKILLspamspam@spam@DATALINK.CH>
To: <PICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Monday, January 31, 2000 6:36 AM
Subject: Re: Comments and questions about DS1820

Peter,

I assume from your comments that you are powering the 1820's positive pin
with the local regulators output.  Were you having problems with inaccurate
readings even though you supplied 5v to the + pin over the cable?   My
problem comes when I try to operate in the two wire, parasite power mode.
If I supply +5v to the device, through the cable, my readings seem fairly
accurate.


> I had the same problem on a Cat.5 cable of 100 feet length.
> My solution was:
> Supply +24V over the cable and have a 5V Lin.Regulator at the end where
the
> sensor is.
> Peter

2000\02\02@061638 by Peter Keller
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Rod Phillips schrieb:

{Original Message removed}

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