I initially asked this as an 'answer' to an existing thread on DS18B20 temperature probes as it seemed the obvious way to ask a question of people who were connecting the probes to various hardware. However this was deleted as it wasn't an answer, so here goes, again, as a straight question. I have been trying to create a fairly extensive 'network' of DS18B20 sensors in a house for remote monitoring and wondered whether anybody had any idea whether there are any limitations to the number of DS18B20s that can be connected together on a 1 wire bus.
I understand that bus length could be an issue as well as topology of the bus but in trying to set the sensors up on a breadboard to test I discovered that once I had reached a total of 10 sensors any additional ones I inserted on the breadboard only displaced one of the earlier ones I had on the line. This seems to be an internal maximum associated with the drivers (from a prior post). Using the command:-
only ever lists 10 devices at once even when there are more than 10 attached at it seems to be the last ten that are visible.
In continuing the quest I tried wiring up the various probes around the house/cellar connected it all up and found that only two of the 5 installed were registering in the OS. Starting again and wiring them one-by-one (of course, I should have done this first!) I reached a maximum of 4 and when the fifth wire was attached they all dropped off, again. So I'm now down to 4 working but interested in knowing whether there is a way to add more to the "1-wire" bus that I have in place, or should I add another wire through another port or have more 'power' available...
So the question may be more "How many can a single Raspberry Pi handle?". Has it more (or as much) to do with the power drain through the +3.3V pin on the GPIO? Or the topology of the wire (how long, how many nodes etc)... If so any ideas what the maximums might be - ie number of nodes, length of wire, type of nodes (single lines off a backbone or star groups off at the nodes). What set-ups are others using?