Pas Home / 1-wire vs Tektronix oscilloscope

RE: Pas Home / 1-wire vs Tektronix oscilloscope

verrverr — Fri, 29 Aug 2014 22:03:40 GMT

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.

RE: Pas Home / 1-wire vs Tektronix oscilloscope

kipe — Fri, 29 Aug 2014 12:28:54 GMT

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.

[View:/resized-image/__size/620x395/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-acc9ce1a-d1ce-4703-a5a1-205b5b741bd8/3603.contentimage_5F00_177019.jpg:620:395]

[View:/resized-image/__size/620x395/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-acc9ce1a-d1ce-4703-a5a1-205b5b741bd8/0550.contentimage_5F00_177020.jpg:620:395]

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.

RE: Pas Home / 1-wire vs Tektronix oscilloscope

mcb1 — Fri, 29 Aug 2014 08:51:09 GMT

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

RE: Pas Home / 1-wire vs Tektronix oscilloscope

kipe — Fri, 29 Aug 2014 06:35:44 GMT

Have you thought about using a DS2482 as a controller? It's an easy way to connect Onewire to I2C, and avoids the problems caused by bitbanging the Raspi GPIO.

You can get the chip as sample from Maxim and it's quite easy to use. I'm currently designing a board to connect to Raspi which uses this chip and I've tested it on breadboard without any problems.

Using the chip would also reduce the number of external components as well as give you active pull-ups, so the communication should stay a lot cleaner.

There's some notes on using the DS2482 in the Guidelines for Reliable Long Line 1-Wire Networks which are worth checking out.

I've been using DS9490R for Onewire-networks with cable lengths up to 40 or 50 meters without any problems. The sensors (DS18x20) have been parasite powered with no external components (no pull-ups, series resistors etc), just connected to the DS9490R directly. No problems what so ever.

I could try and post a brief blog post about using the DS2482 next week, I've been busy with EPE'14 for the last couple of weeks and really haven't got anything done regarding this project. However, I've had some ideas and now it's time just to get them done [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-acc9ce1a-d1ce-4703-a5a1-205b5b741bd8/contentimage_5F00_403.png:16:16]

RE: Pas Home / 1-wire vs Tektronix oscilloscope

shabaz — Fri, 29 Aug 2014 04:42:57 GMT

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.

RE: Pas Home / 1-wire vs Tektronix oscilloscope

michaelwylie — Fri, 29 Aug 2014 04:27:36 GMT

Do you know the capacitance per foot of the wire you are using?