Dallas temp sensor questions

Projects General Guidance
1

Q1.....How far away from the arduino can the sensor be and still have a reliable signal?

Q2 .... I have 6 sensors hooked to a single buss set to update every 30 seconds or so I notice that the temps of all the sensors don't always change ... in fact sometimes it will go through a cycle or two with only one sensor changing. Is this normal? With the sensitivity set to .01 degrees I would think they would change every cycle?

thanks steve

2

Hi, we need the Dallas Part number so we know what type of comms we are dealing with

Tom........ :slight_smile:

3

They are one wire temp sensors that I got off ebay there is no number. they are DS18B20's
I am not married to these sensors so if there are others that allow for a longer buss I would change.

thanks steve

4

How do you have them hooked up? Do you have a pullup resistor on the data line?
It would also help to see your code (posted in code blocks).

Pete

5

murmsk:
et to update every 30 seconds or so I notice that the temps of all the sensors don't always change ... in fact sometimes it will go through a cycle or two with only one sensor changing. Is this normal? With the sensitivity set to .01 degrees I would think they would change every cycle?

With that sort of loop cycle, I think you would expect a change. If you are using long cables, that could be the problem. DS18B20 are available ready-connected to 5m cables and give no problems There has been plenty of discussion around here on this, and they can work on much longer cable if you decrease the pullup to 2.2k, just don't go cheapskate on the cable like I did. I understand CAT5 will suffice. If your code works with shorter cable, it will work with longer cable and there i s no need to post it.

6

With a steady temperature reading it would be difficult to know whether you're actually seeing live data. The sensors are quite responsive so you could simply touch each sensor in turn and then see how promptly your sketch reports the temperature change. Are you using a standard example sketch, or something you wrote yourself? If it's your own work I suggest you post it in case there's a bug in the logic used to read and display the sensor values.