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[wxsig] Wind Speed Spike

Will Beals will at beals5.com
Mon Jul 10 00:22:23 UTC 2006


If the DS1994 is pulling enough power to crowbar the pullup resistor, then
it is broken.  It should not be doing that.  A good way to tell on the
T238(+) is to look at the status display that shows the bus voltage when you
plug in and remove the DS1994.  If you see the voltage drop when you insert
it, then you know it is for some reason drawing too much current.


-----Original Message-----
From: Joe S. Borovetz [mailto:wa5vms at tapr.org] 
Sent: Sunday, July 09, 2006 4:13 PM
To: will at beals5.com; TAPR Weather Station SIG Mailing List
Cc: jabennett at insightbb.com
Subject: RE: [wxsig] Wind Speed Spike


I am beginning to wonder if pull up is the issue that is killing the one
wire bus when I enabled the DS1994.

The 1994 is trying to draw operating power from the 1 wire bus (even though
there is a 3V internal lithium battery).

>I have three pins on the 1-wire bus in order to provide sufficient drive
>strength for the "active high" state needed for some 1-wire sensors like
>DS18S20 temperature sensor.  The active high state is defined to allow some
>sensors that temporarily need more than the paracitic power provided by the
>pull-up resistor in order perform some function.

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