Hello,
I have a 55 meter 1 wire run. Device search yields no devices. It's Cat 5 wire. GND Blue, Signal Blue/White, +5v Brown/White. Other wires floating. Device is a single DS18B20. Measuring voltages on the far end shows 4.69v on the +5 volt line, and fluctuation between 4.4 and 4.69 v on the signal line.
A short 10 meter star topology with using straight thermostat wire and 5 DS18B20 works fine.
Help!
Are the blue and blue/white paired ?
That would introduce a lot of capacitance between the signal and the ground.
Could you do a test:
Use one pair (two wires) for GND.
Use one pair (two wires) for the signal.
Use one pair (two wires) for +5V.
One option to consider is to use an Arduino (Tiny?) as a repeater, somewhere halfway and use another protocol for the length,
e.g. an DS18B20 takes 100 ms to read so serial over 19200 baud is fast enough to send a few bytes in the same time.
The low baud rate will be more robust than ...
Thanks for the replies. Erdin: I tried several different pair combinations. I was surprised to find that using white blue to Signal and white brown to ground (parasitic mode) worked. Joining twisted pairs (white blue and blue) did not work. The parasitic mode with a wire from each pair is the lowest possible capacitance. This led me to consider the RC time constant. I was using a 5.3 k ohm resistor for my pull-up. Switching it to a 2.7k made my original configuration work. I understand that 1000 ohms is minimum. Problem solved.
This article was extremely useful in thinking thru my problem:
http://www.1wire.org/Files/Articles/1-Wire-Design%20Guide%20v1.0.pdf
http://www.108relays.ca/art_cable.html
