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predrage
Joined: 23 Jul 2005
Posts: 132
Helped: 5
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 28 Jan 2008 19:30 1-Wire cable length |
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| Hi. I am doing some project with iButton and PIC. I would like to ask you what is maximum cable length between iButton and PIC and which type of cable should I use. I am a little afraid of EMI because a long cables should be connected directly to several pins of PIC. What is yours experiences?
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FvM
Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany
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28 Jan 2008 19:48 Re: 1-Wire cable length |
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Hello,
I think, unshielded twisted pair should be o.k. for most applications. E. g. Conica-Minolta uses it inside photocopier/printer to access toner id-chips, could be 1 m cable length for each chip, several connected in parallel at controller board.
I remember, the topic is also widely discussed in some Dallas application notes.
Regards,
Frank
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predrage
Joined: 23 Jul 2005
Posts: 132
Helped: 5
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28 Jan 2008 20:09 Re: 1-Wire cable length |
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| FvM wrote: |
Hello,
I think, unshielded twisted pair should be o.k. for most applications. E. g. Conica-Minolta uses it inside photocopier/printer to access toner id-chips, could be 1 m cable length for each chip, several connected in parallel at controller board.
I remember, the topic is also widely discussed in some Dallas application notes.
Regards,
Frank |
Cable length that my application required is approximately 15m in noisy enviroment (mostly fluo lamps). Can you point me to that application note. I skimed through some today and didn't find anything useful.
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FvM
Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany
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28 Jan 2008 20:26 Re: 1-Wire cable length |
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Hello,
in AN244 "Advanced 1-Wire Network Driver" cable length up to 100 m is discussed. Noise immunity of 1-Wire-Protocol is said to be based on integrity checking and retranmission when necessary, see app159 "Ultra-Reliable 1-Wire Communication". To my opinion, If the fluorescent lamps aren't switched on and off permanently, you have a good chance of succesful transmission after one or two retries at maximum.
Regards,
Frank
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predrage
Joined: 23 Jul 2005
Posts: 132
Helped: 5
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29 Jan 2008 11:36 Re: 1-Wire cable length |
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| FvM wrote: |
Hello,
in AN244 "Advanced 1-Wire Network Driver" cable length up to 100 m is discussed. Noise immunity of 1-Wire-Protocol is said to be based on integrity checking and retranmission when necessary, see app159 "Ultra-Reliable 1-Wire Communication". To my opinion, If the fluorescent lamps aren't switched on and off permanently, you have a good chance of succesful transmission after one or two retries at maximum.
Regards,
Frank |
I am reading iButton often is possible and I'm doing crc check. Thats not a problem. I am consider of eventual strange behaviour of PIC (reset, buging...)
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FvM
Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany
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29 Jan 2008 13:07 Re: 1-Wire cable length |
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Hello,
yes, the PIC interface should be mainly protected against voltage transients, that could probably damage it. Also high frequency interferences should be supressed. I think, that the "Advanced 1-Wire Network Driver" circuit is a good starting point. To suppress interferences, a common mode filter could be meaningful.
Regards,
Frank
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zolciak
Joined: 29 Jan 2008
Posts: 1
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29 Jan 2008 14:27 1-Wire cable length |
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hello,
max 10m for ds18b20
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FvM
Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany
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29 Jan 2008 15:44 Re: 1-Wire cable length |
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| Quote: |
| max 10m for ds18b20 |
Where did you get this from - not from Maxim-Dallas, I think.
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