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DS18B20 – 2 wire configuration – 2 Temp Probe — inconsistent results June 18, 2011

Posted by rik94566 in aquaponic automation, aquaponics, arduino, CAT 5 Cable, DIY aquaponics, DS18B20, Hacks, indoor aquaponics, indoor duckweed growing, indoor gardens, indoor growing, Rj45 connector, sensor, Sensor Hub, Stainless Steel Temp Probe, Standards, Temperature Probe.
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Being that I have a testing platform and the fact that I want to learn everything there is to know about how the DS18B20 behaves and performs I decided to test a 2-wire configuration using 2 temp probes.  Results were inconsistent.

Here is how I configured the RJ45 testing hub.  I kept the arduino side the same as in the last blog post and only changed the wire configuration on the hub side.   I configured the hub the same way for both position 1 and 2.

2-wire configuration at hub

The inconsistent results were generated only on position 2 of the hub.  I have no idea why this occurs.  It seems to be at random as to when it occurs in the cycles of the sketch.  With results that are inconsistent it is clear that it is not a good idea to use this for important work.  For 2 or 3 cycles normal temperatures report out and then the 185.00F is reported out.  Strange stuff.

I am using the same Sketch posted earlier for testing 2 Probe DS18B20 sensors.

Resuts from Sketch (inconsistent results Probe 002)

Doing a little research I found that inconsistent results are experienced when adding multiple DS18B20 sensors when using the parasite power mode, which is the 2-wire configuration I have working here. I will test other situations now and try and determine issues with this power modes and configurations



1. David - August 6, 2011

I imagine you’ve figured it out by now, but I had this issue and it was because I was polling too quickly. I put a delay of 4 seconds between each sensor’s read and between each iteration of the loop, and that took care of it. Got this information from here, in the Troubleshooting section:


David - August 6, 2011

Great blog BTW, I’ve been inspired by it and intend to appropriate your CAT5 idea for a koi pond automation project.

rik94566 - August 13, 2011

David – thanks for this input. I will try your suggestion. Writing code is not one of my skills set, so I see what I can do. I will publish my results. Have you been able to be specific with the device index on the IC’s? When I change the probes around the code does not pick them up or there locations.

David - August 23, 2011

I have not yet tried to change the probes around… I don’t get how the addressing / discovery works and I’ve been afraid to mess with it.

rik94566 - August 25, 2011

David – I agree with you on this point. I have moved the probes around without causing any electrical issues. The issue I see is as you have pointed out, is in the addressing of the probes. I have found that the first probe no matter what is always read correctly, but I will get a 185 F reading on the second probe many times. I always get this reading when a disconnect occurs or if I unplug a probe and then re-plug back into the same jack. There is not a lot of work done on the libraries as far as documentation to address this issue of how the probes are read and in what order. It seems to me that the library reads the individual HEX code of the probes and assigns them in the device_index. Since I can not found much information regarding this on internet searches, I have moved to a different strategy and one that is more main stream in the current body of work on the internet. I will be blogging about my new direction now and would like to see what you think or explore some of your ideas. Let me know. Thanks for the input and lets figure this out so others can get meaningful projects completed without a lot of research and experimentation while learning from each other.

David - August 26, 2011

Sounds good, I look forward to seeing what you’re working on. I haven’t had the time to play with it recently, been moving. I’d like to have a look around what how the indexing works when I have a chance, if I can find anything on it…

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