On Apr 16, 8:23*pm, "DoN. Nichols" wrote:
On 2011-04-16, Karl Townsend wrote:

I built a serial port temp. sensor years ago based on this fella's
work:
http://quozl.netrek.org/ts/

And just bought kit 145 from carl's electronics:
http://www.kitsrus.com/pdf/k145.pdf

The unit uses DS1820 temp sensors and connects to the pc serial port.
There is a fifty foot run from the computer to the sensor.

* * * * O.K. *First off -- I would shield the run to the computer -- at
2400 baud, the data rate should be able to handle 50 feet with no
problems. *Ground the shield (pin 5 on the connector shown), and connect
the other two wires to the shielded twisted pair.

* * * * How far are the sensors from the board? *If you are using only
one sensor, and it is mounted on the board, this should be enough. *(Put
the board and sensor in a cage made of brass screen material soldered at
the seams and connected to the gound pin.

* * * * If you are using multiple sensors, use another shielded twisted
pair to each sensor -- again with the ground pin (pin 1) connected to
the shield. *I don't know how fast the data on pin 2 is, but that and
the capacitance between the pin 2 lead and the shield would determine
the maximum safe line length.

My better half made me quit using it because of AM radio interference.
There is a constant beep beep beep.

* * * * This is probably the communication between the sensors and
the board. *The longer the wires, the greater the amount of radiation.
Find some shielded twisted pair to shield each run from the board to the
sensors, and from the board to the computer. *This will probably reduce
the maximum line length but if you aren't using really long lines
anyway, it should work.

* * * * You can use some of the cable used for Cat5 network runs between
the hub/switch and the wall jacks for the ethernet -- if there is a foil
shield around the twisted pair -- usually with an uninsulated drain wire
making contact with the foil shield. *Just make sure that this is
connected to the ground pin on each connector, and you should be in
pretty good shape.

I'm once again in need of 24 X 7 temp. logging. Is there an easy way
to salvage this unit? Or am I better off to just start over with some
sort of analog unit?

* * * * Try the shielded lines first. *They will probably fix most of
the problems.

* * * * Enjoy,
* * * * * * * * DoN.

--
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Don (and everyone else) -

Seriously, folks. If Karl REALLY needs to monitor the temperature
CONSTANTLY, then all this shielding and grounding and filtering would
be the way to go, BUT, how fast is the temperature going to change? A
couple of lines of code and you can toggle DTR when you want a
reading. I can't imagine any drastic temperature changes occurring in
less than a few minutes. Just take a reading and go to sleep for a
while. Nobody's going to notice a tiny burst of RF every 15 minutes.