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Last update:
July  2021 (74)


Cabling for 1-Wire sensors

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 available here  

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 lead.  
         - take another twisted pair, and connect the sensor V+ pin to one lead.        

  Cat5_cable_connect.jpg (28524 bytes)

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. 

  Flat tel cable connect.jpg (28299 bytes)

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  would be.  Experiment!  

 - 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 samples."  
        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 down. 

 - 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 revised documentation: 
            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) 







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