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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

Parents

  • I don't use 1-wire enough to know, but it definitely looks like the pull-up is insufficient, and needs to be a far lower resistance, maybe halve it, as a test? (Assuming you can do that according to the spec).It definitely doesn't look healthy : ( could perhaps need a bypass capacitor in case these devices are resetting since bit spacing looks odd. In general that should be 100nF ceramic, and possibly some small electrolytic too. At least a 100nF ceramic by each device.

Comment

  • I don't use 1-wire enough to know, but it definitely looks like the pull-up is insufficient, and needs to be a far lower resistance, maybe halve it, as a test? (Assuming you can do that according to the spec).It definitely doesn't look healthy : ( could perhaps need a bypass capacitor in case these devices are resetting since bit spacing looks odd. In general that should be 100nF ceramic, and possibly some small electrolytic too. At least a 100nF ceramic by each device.

Children
  • 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

  • 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