Cabling for 1-Wire
I couldn't find an official statement on
the Maxim/Dallas 1-wire website, but Cat5 network cable seems to be the generally
accepted cable type for connecting 1-wire devices.
This document is a
must-read if you are going to be using long cables:
1-Wire Design Guide (discussion of cabling issues) pdf
1) A Cat5 cable has 4 twisted
pairs. Connections would go like so:
Take 1 of the twisted pairs, and...
- connect the sensor data pin to one lead,
- and connect the sensor ground pin to the other
- take another twisted pair, and connect the sensor V+ pin to
2) Flat telephone cable can also be
used. This does not have twisted pairs, so needs a
different approach: there
should be a grounded conductor between the data line and the
V+ line. This acts
as a shield, reducing the possibility of interference from external sources.
Maximum cable length unknown.
3) Another option is 2-conductor
shielded cable (eg: microphone cable). I've used this
successfully on short
cable runs (25 ft). Longer runs should be possible, but there will
eventually be too much signal degradation, though I'm not sure where the cutoff point
- The K145 documentation states "200 yards" (~600
ft). I wonder if this might be a typo.
Maybe it was meant to be 200 ft. (~61 m)?.
(one K145 software user has reported using
cable runs of 200 ft)
- Quozl ( http://quozl.netrek.org/ts
), the designer of the K145
circuit, suggests a 10uF
Tantalum capacitor be placed across the power
supply pins of the temperature sensor.
This "tends to provide more consistent
measurements. To put it another way, if you
remove it you may get random error in the
On shorter cable runs, this may not be such
an issue. Addendum: it actually may still
be an issue on shorter runs. I have
seen Min/Max values bounce all over the place
(extreme highs and lows that don't fit)
when there is no capacitor at the sensor. Hooking
up a capacitor seemed to settle things
- Some people have suggested grounding unused leads in a cable. The
document above (top
of page) says don't, as this will
increase capacitance, which increases loading, which
degrades the data signal.
- The K190 requires a resistor and the capacitor to be added at the sensor on
cable runs over
25 feet (7+m.) in length. See the updated
K190 documentation for further info.
These are the max cable lengths posted in the
Twin-shielded audio cable - 15 metres (~50 feet)
Flat telephone type cable - 75 metres (~245 feet)
CAT5 cable - 100 metres (~325 feet)
(with capacitor and resistor added)