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DS18b20 Weird Behaviour

Posted: 02 Feb 2019, 02:32
by gregoinc

I recently setup my NodeMCU with 2 x DS18b20 units based on this wiki page: ... alibrating

The 2 x DS18b20 were connected (as per the wiki page) via a short Cat5e cable utilising RJ45 sockets, then each of the DS18b20 had an RJ45 plug attached to the end of the cable that came with the DS18b20 (the cable is approx 40cm long). On the prototype breadboard I used a 47K ohm pullup resistor. Everything worked as expected and I had the following on the Devices screen.
Temp All Good.png
Temp All Good.png (88.98 KiB) Viewed 893 times

I then ran a Cat5e cable approx 5 meters to the location where I wanted one of the DS18b20 to be located. After plugging everything in I found this on the Devices screen.
No Temp Display.png
No Temp Display.png (88.42 KiB) Viewed 893 times

Here's what Temp2 looked like in the devices screen... note the address of the DS18b20 is gone?
Temp2 Detail.png
Temp2 Detail.png (102.23 KiB) Viewed 892 times

I then unplugged the 'local' DS18b20 and left the DS18b20 connected to the 5 meter cable, the DS18b20 at the end of the 5 meter cable was working and providing temperature readings. I plugged back in the local DS18b20 and everything stopped working again??

The power to the 2 x DS18b20 is setup as per the wiki page above.

I am sure the issue is a simple one... but after reading mutiple forum pages I am no closer to a solution. I suspect it is a 'power' problem... So do I change the power supply (I am using a USB style 800ma plug pack power supply connected to the NodeMCU), or connect directly to the DS18b20? Do I change the pullup resistor?

Advice appreciated?

Thanks, Mark

Re: DS18b20 Weird Behaviour

Posted: 02 Feb 2019, 02:54
by gregoinc
As an update... I have noticed intermittent times when the Temp2 sensor is not contactable. Here's the log screen:-
logscreen.png (51.69 KiB) Viewed 887 times
Thanks, Mark

Re: DS18b20 Weird Behaviour

Posted: 02 Feb 2019, 09:17
by gregoinc
Ended up completely rewiring based on feedback from Grovkillen, changing the pullup resistor, and the issue appears to have disappeared. I suspect the root cause was operator error :)