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Author Topic: 1-Wire Vcc GND - connect to Data GND on sensors?  (Read 362 times)
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Hi,

I'm a little confused.
The suggestion is to use one pair of the CAT cable for Data and Data GND
and another pair for Vcc (5V) and GND.

Does that mean on my sensors i connect them together?
If not i think the extra GND for Vcc would be useless.
But on this premade DS18B20 they just pass the GND through: http://www.fuchs-shop.com/download/manuals_for_t-sense_05-22-08.pdf

In the attachment are my own sensor circuits - there you can see better what i mean.


* 1wire.GIF (16.86 KB, 1286x909 - viewed 31 times.)
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The suggestion is to use one pair of the CAT cable for Data and Data GND
and another pair for Vcc (5V) and GND.

Whom's suggestion? Link?

It does make sense though because Cat 6 cable is twisted pair-wise. Having a GND on every pair makes the transmission more robust, even if you connect both together on both sides. BTW, you don't need two pairs, one is enough if you run the devices in parasite mode.
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There are allot of places...
For example: http://1wire.org/index.html?target=p_2.html&lang=en-us
and: http://www.fischer-net.de/hausautomation/haustechnik/1-wire/26-1-wire-belegung-kabel-stecker.html

I don't like parasite mode - extra 5Vcc is more stable and the CAT cable has enough wires smiley

Sure, the idea is to also shield the 5Vcc - but nowhere i found what to do with the second GND.
It only makes sense to me like i draw it. If you only connect one side you have a big antenna.

I was looking for a circuit off a ready made sensor from some company's to see what they to.
But sure, they don't show it that you don't steel there circuit.
Also all the PCB pictures are so blurry and small that you see nothing.

I already made the temp sensor from my circuit on a 0,32x0,98" veroboard (damn that 0805 SMD ferrite bead is small).
Now i need to solder the sensor to the CAT cable (for the in-floor heating) that i can lay my laminate floor and then i have
no longer access to it.
Unsure what to do with the GND.
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These are references that suggest that wiring if you use cat 5/6 cabling and RJ45 connectors.
Cat 5/6 cables make sense if your devices are quite far away, they are a waste of material if the distance is less than half a meter in a not so noisy environment.

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I don't like parasite mode - extra 5Vcc is more stable and the CAT cable has enough wires

I agree but you seemed to have a problem with the extra GND wire.

Quote
Sure, the idea is to also shield the 5Vcc - but nowhere i found what to do with the second GND.
It only makes sense to me like i draw it. If you only connect one side you have a big antenna.

In the circuit you drew it's the only wiring that makes sense, I agree. But it's possible that you physically separate the power supply and the signals, then you need to have separate GND lines.

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I already made the temp sensor from my circuit on a 0,32x0,98" veroboard (damn that 0805 SMD ferrite bead is small).
Now i need to solder the sensor to the CAT cable (for the in-floor heating) that i can lay my laminate floor and then i have
no longer access to it.
Unsure what to do with the GND.

Connect both grounds. Circuits simple as your's have to do that. For your application it doesn't make sense to add any more components to separate the power supply from the signal side (p.e. opto couplers).
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Cat 5/6 cables make sense if your devices are quite far away, they are a waste of material if the distance is less than half a meter in a not so noisy environment.
Looks like thats not really the case.
Dallas recommendation is UNSHIELDED CAT5 cable and to not use shielded cable as the capacitance increases.
You can read stuff like (from 1-Wire-Design Guide v1.0): For short runs (where the total length of the 1-Wire bus is < 30 meters and the network only has a few slave devices on it), cable selection for use on the MicroLAN is reasonably simple, as even flat modular phone cable can work with a small numbers of 1-Wire slave devices.
On the other hand you have people who have problems with just 20 meters and CAT5/6 where you can read in docs that
100 or 200 meters shouldn't be a problem.

Then you can read:
Grounding unused wires or shields in a cable adds capacitance, which can significantly increase the RC time constant, they should be left disconnected. You want to limit capacitance throughout a 1-wire system as much as possible to maximize cable length and limit RC effects. Dallas Semiconductor recommends that unused wires and shields be left unconnected at both ends of the cable. The wires should be left floating.
But then you have the docs from companies that sell 1-Wire systems that make recommendations like i showed you.
Also some say "loop the shielding trough" others say "loop the shielding trough and connect it on one side".


When i looked at 1-Wire first before 2 years and decide to use it everything was clear.
Now i have everywhere CAT 6 for everything cause its relatively cheap.
It's time to connect now everything and maybe i was reading to much in forums and
on seller stuff and it confused me.

If i look at Dallas/Maxim and "1-Wire-Design Guide v1.0-1" or "1-Wire Application Guide 1.03" i think
its best to really just use 3 wires (DATA/GND/5Vcc).

Only thing is that i used shielded CAT6 and didn't even know that unshielded CAT6 exist.
I know that in the U.S. they use allot of unshielded CAT5 (UTP) cable but CAT6 UTP is new to me.
Here in Germany since years shielded cable is standard.
Even for my AC power i used shielded cables to have no EMC/EMI between them and my Network/Home Automation.

Hm, so the only question left is: To loop or not to loop the unused wires and shield from slave to slave.
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How long is your wire then? Did you check with the cat 6 cable? I also don't know of unshielded cat 6 cable.

I had 1-wire connections using twisted signal/ground cable (parasite mode) with a length of over 20m (unshielded) without any problem. In an electrically noisy environment you probably won't have success with such a cabling variant but in my home it worked well. So the best advise I can give to you: Try it in an environment as identical as possible to the final installation and look what results you get with cat 6 cables and simple telephony wires. Use the solution that gives you the better results. If you have noisy equipment (an Apple power supply is a very good source of much electrical noise) you can better live with the increased capacity of the cable than with the signal degradation you get from the noise.

If both is not working, move the Arduino (or maybe a simpler ATtiny) beside the sensor and change the remote connection to something more reliable (p.e. RS485).
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beside the sensor
Then 1-Wire would not make sense smiley

I don't sum it up yet. But 15, 20,  30 meters is nothing in a house.
From living room to bed room 8m...
From bed room to bath room 8m...
To the sensor and back in the cement flooring is 4+4=8m
That alone makes 16 meters!
Then i go to the windows (each 2 reed switches and a glass breakage detector)...

I found one guy who uses the Loxone Smart Home Automation and has 1 ring
for each floor of his house. Every window, door, temp in every room and so on...
And Maxim writes about 100, 200, 500 meters - so it should not be a problem if you do it right.
But now i have S/FTP PiMF everywhere and its to late cause i thought its the best.
I use CAT6 for one wire and my light switches and CAT7 for Ethernet.

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Try it in an environment as identical as possible to the final installation
How can somebody to that? How to replicate all the wires/electric in your house (walls, ceiling)?
Especially if you just start to build your house...

No Apple stuff in da house smiley-evil

I extra bought two books about EMC/EMI from VDE (http://en.wikipedia.org/wiki/Verband_der_Elektrotechnik,_Elektronik_und_Informationstechnik)
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