I tried to build a temperature sensor with a few DS 18B20 distributed in the house. So I build the needed 4k7 resistor on a breadboard and connected the 3 required cables to a RJ45 patch panel, using pins 1=5V, 2=Data, 6=GND. This works perfect when the sensors are "near" the arduino. A few meters is no problem, every sensor delivers perfect data, so sketch and cabling seems to be OK.
Then I tried to put one sensor more far away, using the cables in my house. But then nothing works anymore, there are no readings anymore.
The OneWire-Bus seems to crash, when cables are too long. There are some documents on the MAXIM-Website concerning a long-range network, but it is also statet, that it might be possible to change the timing a bit.
I already tried to tune the "read_bit" timings a little bit: I again get values from the sensors, but these values are wrong (bad CRC).
Has anyone build a network with a longer range / weight and One-Wire-Bus?
edit: some pictures and a german description can be found here: http://camino.dirk-melchers.de/2009/04/12/arduino-temperatur-sensor/