-
I've used DS18B20s at 3.3V with 4.7K without issue before. I think it's a timing issue. It seems as if the master (the MDBT42Q) sometimes drives the one wire signal low for longer than spec and/or doesn't sample the slave device response in time to get accurate data and, consequently, gives up during the search. The same issues would render the data reads unreliable. But this code doesn't even bother with that issue. Doing a search and getting a reliable response is fundamental to a reliable OW interface.
However, having said all that, I will try a 3.3K just 'because'. :-)
Also, to answer your question, reliability didn't seem to be affected by whether there was one probe or two plugged in.
Also, I noticed when looking at the traces, that the search code does a Reset as well, so the one I have in this code is redundant. I don't think it would cause issues with the search but I'll remove it.
Tom
You are reading a single comment by @TomWS and its replies.
Click here to read the full conversation.
TomWS
If you are using two sensors on the same pin - you only need one resistor - you don't want it on both.
Is vdd 3.3v? If so a 3.3k resistor might be better.
If it more reliable when you only connect one sensor at a time?
Also - comment out the reset - that might be causing an issue before the search.