Am Montag, 18. September 2006 23:18 schrieb Philipp Haeuser:
>
> Is it sufficient to daisy-chain the DATA line, and can GND and +5V still
> remain in "stubbed" topology, or should I run all of these wires through
> (i.e. back and forth via separate wires) all of the sensor cables, too?
>
Onewire Data and GND lines must be wired together as a bus. 5V may be wired
any topology.
But there may be another problem: The current drawn from the 5V line must run
back to the supply through the GND line. If your cable is long, the GND wire
is thin and the current is high (>100mA), the GND potential at the end of the
bus may be not quite 0V, but >0.7V, which could lead to the problems
described, too.
So you should use a local power supply for the your sensors, or use several
wires for the GND line -- properly in bus fashion.
> Either way is possible, as I've got 4 wire pairs per sensor cable.
>
Pairs are 1-2 3-6 4-5 7-8. FAR is the Far side of the bus, HOST the host side.
1 1W_DATA_FAR
2 1W_GND_FAR
3 5V_HOST
4 1W_DATA_HOST
5 1W_GND_HOST
6 1W_GND_HOST
7 5V_FAR
8 1W_GND_FAR
The idea behind this is:
* DATA and GND are paired
* END and HOST are not paired
* 2 GND_END and 2 GND_HOST lines.
* only one 5V line.This is sufficient, as the voltage drop on the GND line is
limiting the 5V current anyway.
> Should GND and DATA go twisted with each other?
>
YES
> Or data[going to sensor] on the same twisted pair with
> data[coming back from sensor] ?
>
By no means!
Kind regards.
Jan
--
"If the future navigation system [for interactive networked services on
the NII] looks like something from Microsoft, it will never work."
-- Chairman of Walt Disney Television & Telecommunications
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