Am 31.05.2016 um 19:00 schrieb Guy COLIN:
> Hi Jan,
> thanks for considering my (small) problem.
>
>> Double listing of devices means the "Search ROM" trickery fails. Most
>> likely because it's very fragile on any bit. No checksums at all.
> No CRC at all? I thought there was a CRC in each ROM number?
>
The "Search ROM" mechanism can't have a CRC because it is a wired-AND on
the bus line. Neither the host nor the slave know the result of the
ANDed bits in advance.
>> You don't have a star topology cabling, do you?
> No everything is daisy chain
>
Good. So no problems from that.
>> Do you have homebrewn slaves in your bus?
> No only commercial devices.
>
There are commercial devices with homebrewn chips out there.
> On this Raspi the bus master is a DS-2482-800 That's I2C->1wire 8 channels
> Here is my bus listing:
> /mnt/1wire/bus.0/bus.0/:
> 29.1C9E09000000 (DS-2408 LCD driver (by hobby-boards))
> /mnt/1wire/bus.0/bus.1/:
> 3A.546302000000 (DS-2413 PIO start/stop house heating gas boiler)
> 3A.B36002000000 (DS-2413 PIO start/stop 12V power for LCD)
> /mnt/1wire/bus.0/bus.2/:
> 10.9702E6010800 (18S20 temp sensor inside this Raspi box)
> /mnt/1wire/bus.0/bus.3/:
> 10.B6FAE5010800 (18S20 temp sensor inside humidity sensor case)
> 26.FFD8F1000000 (DS-2438 + humidity sens. (by hobby-boards))
> 28.4E3066020000 (18B20 temp. sens. living room Ref. for heating)
> /mnt/1wire/bus.0/bus.4/:
> /mnt/1wire/bus.0/bus.5/:
> /mnt/1wire/bus.0/bus.6/:
> /mnt/1wire/bus.0/bus.7/:
>
Looks okay.
> The longest cable is the one on bus 3: I have a CAT5E network cable 5m or 6m
> long going to a junction box where it's connected (soldered) to a 3m
> telephone cable of same cross section than CAT5 cable (also twisted pair).
>
That's okay, but keep in mind for later installations twisted pair is
BAD for onewire. Twisted pair is only good if the drive is symetrical.
For asymetrical drive as with onewire, it only adds cable length and
capacity.
> In these cables 1 pair is used for 1wire DQ+GND and 1 wire from another pair
> is +12V to power the Humidity sensor (power consumption is 2.83mA).
> Note that as per the hobby-board doc (link here above) it's possible to use
> parasistic or external power. I have tried both. But I got wrong humidity
> values with parasistic power (humid. around 10% lower)
>
The reason why I ask about that is ground lift. If you power e.g. a
display backlight or a solenoid through the bus cable (regardless if you
have separate power wires), you may get several 100mA of current flowing
back to the host through the ground wire, which may lead to a ground
lift of more than 0.5V over the length of the cable.
This can make the devices on the far end of the bus become invisible,
because when they pull "their" GND to 0.2V, on the host side it becomes
0.7V which makes it impossible for the host to "see" that pull to GND
from the slave.
If power is as low as 3mA, you don't have to worry about this.
>
> Side note: I used to have my external temp. sensor on this bus.3 as well,
> but it was connected from the junction box by another 3m cable. So it was a
> kind of star topology:
> 1x5m cable from bus master to junction box then 1x3m (Extern. temp) + 1x3m
> (Humid+ Intern. temp). But 3m isn't very long and it has worked fine for
> years (months?).
>
3m should work.
> When I started to miss measures I put this external temp sensor on it's own
> cable from the bus-master and on it's own bus (bus.7). But it didn't solved
> the problem.
> This external temp sensor was the most missing. Even with its own cable and
> own bus! So a few weeks ago I moved it to an arduino connected by serial to
> the raspi, then everything is ok.
> But I don't want to keep this. This sensor must go back to the raspi. When
> troubleshooting my system I'm planning to connect it back to the raspi to
> see if I can catch something.
> Note that when I'm talking of missing measure it's usually not a lot, I can
> stay for weeks without problem then for a few hours it's missing.
>
Check the cabling. There isn't much more to say to it. Check the cabling.
Kind regards
Jan
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