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Topic: Multiple DS18B20, read problems (Read 9954 times) previous topic - next topic


I've wired my sensors exactly like this:

And now you are talking about cabling, which is just as well, as that could be the problem - bad cables and bad connections. The 127 suggests sensor not connected but I guess it could also mean  "connected but unreadable".

You might be better off proving the point with the breadboard setup you alluded to.

Having said that, I got caught short with my local installation and chanced using 1.2m of cheapo four-conductor I had to hand. I think it worked, but luck, the short length, and an electrically-quiet suburban environment probably had lot to do with it.


I've connected it all on a breadboard, but the sensors have 1.8m cables that they where delivered with.

So I solved the problem with faulty readings when touching the cables, it seems to have been bad grounding that was the problem. I found them to be very stable if my computer (laptop) was not plugged into an external power source and i used a 9V battery to power the arduino.

Still I have the problem where if both sensors are connected I cannot get a reading above ~84C. If I disconnect one sensor when that happens I get the values just fine.


Could be inadequate power.

The power-on reset value of the temperature register is +85°C and I think I saw it when I was starving it with supply via USB.


Apr 30, 2013, 07:46 pm Last Edit: Apr 30, 2013, 08:24 pm by Pinky Reason: 1
That might be it. I gotta admit I'm new to the electronics-part of this. I do have a separate power supply that can give me 5 or 9V and 1.5A. Got any wiring suggestions, or should i just plug it to the external 9V power-connector on the arduino?


No wiring, just check the polarity and use 9v. The 1.5A is plenty. Don't be tempted to use the 5v. It sounds kosher but it isn't enough for the on board regulators to do their job, and there is no need to tempt fate by applying it directly to the Vin pin.

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