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  • Author Author: verrverr
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Pas Home / 1-wire vs Tektronix oscilloscope

verrverr

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Hello, this week I did a lot of testing and debugging with the oscilloscope. I try to see and solve the problem of my network of temperature 1-wire sensor.

 

 

I try first to change my connection to the 5v and 3.3v use, I also change the cable connection together. Using the 5v is really not advise for raspberry pi but its still work reasonably well for 6 months.

Result : failure no captor are detected

 

imageimageimageimage

 

Then I tried to change the way power sensors using the parasitic mode. As some suggest me in another post

Result : no difference, no captor detected

 

Here are some screenshots of what I normally should have as working signal

With 1 sensor on 3.3v

imageimage

With 1 sensor on 5v and level switcher

imageimageimageimage

According to this guide Guidelines for Reliable Long Line 1-Wire Networks - Tutorial - Maxim my curve have slow rise time and maybe some reflected problem


Finally I retest on 5v but with a level converter https://www.adafruit.com/products/757 to send only 3v on raspberrypi port

Result : Success all captor are detected and all communicated data are correct

imageimageimageimage

Interesting curve. Yellow is the 5v side data and Blue the converted 3.3v result

image

 

I'll do other tests removing resistors supposed to improve communications and see if it really helps and I will also make a soldering version on a perma-proto board.

Do you see anything else that could improve my circuit?

 

Old schematic

image

 

New improve schematic

image

  • in reply to verrverr

    The spec talks about a nominal 5k pullup, and goes further to show a stronger pullup for long conversion times (12bit).

    The sensor needs to be able to pull down the line, and perhaps some of the other one wire devices are not capable.

     

    It almost seems that one of your sensors is drawing too much current, since the rise time is still rounded even at 1.5k.

     

    Mark

  • in reply to shabaz

    Hi i just do some other test with lower pull-up resistance. And really works better. With 2.7K or 1.5K i can use 3.3v directly without level converter.

     

    The spec indicates use 4.7K resistance, is that the use of a 1.5K or lower can break sensor?

    What is the best use of 4.7K ressitance on the 5v to with level converter to 3.3v or use 3.3V with 1.5k or lower ressitance

     

    image

  • First, thank you for your advice


    I dont know the capacitance per foot of my wire. I use existing wire available in the wall use by standard low power thermometer. The cable size is 18avg. It is recommended to use the network cable cat5.


    I will try with lower resistance in my next test.


    I keep DS2482 or DS2482S-800+ option in a backup plan.


    The white background graph are take with OpenChoice Desktop snapshot and i not found setting for the backgtound. Next time i will use more the save option of the oscilloscope. I forget these images and this is why you see some picture with my phone. I also recently found the option for loading .cvs data file with OpenChoice Desktop.

  • Hi,

     

    Managed to measure from my network built with DS9490R, uses 5 DS18B20's (all in parasite mode), couple of AD-converters etc. Cabling is done with random cables found on my desk, ranging from 0.25 mm² to 1.5 mm². The whole network includes about 30 meters of cable.

    image

    image

     

    As you can see from the captures, the active pull-ups work miracles. I'll try and measure the same network with the DS2482 I suggested earlier, although I'm sure the results should be quite similar...

     

    Also, I forgot to mention before, applies only to parasite power: I had problems before, when I was trying to read the data too frequently. The pull-up didn't have time to charge the internal capacitors of the sensors and this caused the measurements to fail.

  • Pacal

    You may have already found this, but if you set the Inksaver to OFF, you'll get the black screen on your saved images.

     

    mark