[aprssig] APRS bit I/O

Wes Johnston, AI4PX wes at ai4px.com
Thu Jun 28 23:04:38 EDT 2007

Just FYI.... I bought a data logger from phanderson a few years back.  It
would scan the bus of one wire temp sensors and send the result in 1/10th of
a degree C.  They were senstive enough that they could "see" a person walk
by one in a hall way.  Or the temp would shoot up if the black case was
exposed to sunlight (ahem..... cloudiness detector would be two of these
temp sensors side by side, one white one black and read the differnce
between them).....

Then one day I got the wise idea that I wanted to trend the useage of the
elevator in my folks house by watching the 3hp motor's temperature.  Well,
the EMF from the induction motor was enough to fry every last one of my OW
temp sensors on that bus.  That was the last day I used one wire temp
sensors until I got the weather station from AAG electronica.

It truely is amazing all the things you can infer from being able to measure
temperature so precisely.  Put one in the flue of your water heater to see
when it's heating.... put on on the hot water pipe outlet 3 feet from the
tank... and when the temp drops below 115F, you know the hot water isn't
being used any more....


On 6/28/07, Scott Miller <scott at opentrac.org> wrote:
> >    Hmmmm, interesting.  According to
> > http://www.maxim-ic.com/appnotes.cfm/appnote_number/187 , you're
> > correct.  In practice, I have some long ( 100 yard ) 1-wire
> > nets with >
> > 15 or so sensors in which I definitely get the ID's back in varying
> > orders, using the DalSemi OneWireAPI libs.  Now you have me curious
> > about the reason...
> Not sure.. I haven't used the APIs myself.  I've had issues with parts
> dropping off the bus at weird times, but I think I've fixed those.  1-wire
> is a seriously annoying protocol to try to debug.  I much prefer to stick
> with SPI when I can.  Not that it's foolproof - I had a prototype on my
> bench last night that started sending commands intended for a FRAM to the
> PLL in the transmitter module!  Didn't seem to break anything, but it
> certainly wasn't on the frequency it was supposed to be.
> Scott
> N1VG
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In theory there is no difference between practice and theory.
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