A week ago I started putting up my first few 1-wire temperature probes. The DS18B20 arrived from China in no time (3 days). Four of them are now in their pockets at various heights of the thermal store. Initially they ran in parasitic mode, ie. without power injector (due to lack of a proper lead to connect to the 6P6C "RJ11" socket of the DS9490R 1-wire-to-USB bridge. So, a 6P2C old telephone cable got me going for a the first few days.) Well, four T sensors worked fine. But I wanted more. The DS9490R provides +5V on pin 1, so I made up a new lengths of cable with a 6P6C plug. And from now the waters muddied.
It appears that the 1-wire cabling is quite sensitive to little mistakes. For instance, you can't have a trailing wire without any termination on the network. So, go from DS9490R to a sensor, then add another half a meter of wire without anything at the end, and the network is dead.
Now, Wylew made a very good point in saying you should put a return wire in from your furthest sensor, otherwise it'll be difficult to extend the network later. Only worked for me when I put a sensor at the end of the return.
The worst are the panel sensors. I mean, it's always the least accessible one, isn't it? I wanted three sensors, on cold end, between the two panels, and hot end. All clipped to the pipes. And since I was outside, I put a forth sensor on and stuck it onto te north side of the chimney to record air temperature. It's about 10m of cable between the tank and the panels. And guess what, it all worked (eventually, after I cut the return wire out). Up I climb again, put the pipe insulation around it, tidy up, ladders down, scaffold tower down, network == half dead.
The four sensors on the roof all but gone. Scaffold tower up again, ladder onto the roof again (getting good at that now), balancing delicately bellywise on the roof's ridge and taking the insulation off again, while her indoors keeps calling "digitemp -w', and hey presto, the sensors are back alive. Squash the wires together again, forgot to bring the insulation tapes to wrap them, hopp-hopp-hopp along the ridge, down the ladder , ..., sensors dead again. Luckily it's time for a brew, and then night descends and covers everything mercifully in darkness.
And I thought the plumbing bit was the difficult part
Klaus
PS Everything in CAT5 UTP cable, four wires connected to: Gnd, Data, Data_return, +5V. All connections soldered and sheathed in heatshrink, then wheather"proofed" in insulation tape. Pipe sensors around the panel have 5cm long silicon insulated wire tails on before connecting to the CAT5.
