DS18B20 Long Cables

[Otti20vt]

Hello
A few months ago I made a couple of ESP8266 boards (Looky Wifi), many times I had problems with the DS18B20 Sensors.
Now i have a Project where a DS18B20 Sensor is 20 Meters Deep in the Ground, the Reading of this sensor was not possible, i got only Read errors.
At home I connected a DS18B20 sensor to the ESP8266 Board, first with a 2m cable that worked and then with a 70m cable what didn't work.
Then I measured with the osciloscope the signal at the end of the line, as you can see on the Pictures the pullup is way too weak @70m Cable!
Lesson learned

ESP8266 DS18B20 Resistor.jpg (2.07 MiB) Viewed 10680 times

Just want share my experience

[pppp33]

Thanks for sharing !
Usually they say "NO WAY" and we don't even try to go beyond specs.....

[TD-er]

Ah good to see it is working with a lower value resistor.
I can imagine the Dallas sensor is now running slightly out of specs, with higher current.

Also test it with the cable unrolled, to see if it may also pick up a lot of noise.
Having it rolled up like this may also act as a filter.

[seb82]

Thanks for feedback.

In addition, in bsb_lan documentation, there is a chapter about DS18B20 with some advices (mainly adding 100nF and 10µF capacitor). To go further, they also refer to a tutorial from manufacturer for very long lines (>100m).

[Otti20vt]

hey guys
for me this 1kOhm pullup definitive work, I connected the ESP8266 today and it worked straight away!
I have an 10m line on the controller then a Stub of 2m with 1x sensor, then 20m line down in the ground.

@seb82
I also tested with a 100nf capacitor and a 100uf, but that didn't work for me.

DS18B20 30m.png (11.5 KiB) Viewed 10526 times