[Owfs-developers] DS2482-800: problem with long wire and DS18B20

[Jan Sennesael]

As suggested in an earlier thread, i changed my setup from a tree, to a bus.
To make it myself easier, i bought a 9bus board from pridopia (1 DS2482-100
and a DS2482-800)
I am not using the DS2482-100, but the first 5 channels from the DS2482-800.
All the sensors are connectes as a bus
Everything works fine, but when i connect my longest temperature sensor
(ds18b20) as the only sensor on a channel i get "spikes" in the reading from
the longer wires (on other channels). When i connect it as the last one on
another bus, that whole bus disappears. (this sensor uses only 4/5 as go and
not the additional 3*6 as return, so it has to be last)

The UTP is approximately 45m long, cat 5e. I am using wire nr 1/2 for
gnd/+5V and 4/5 for 1wire/gnd (hobbyboard pinout). The sensor worked without
problems on the tree setup (with a diy usb master), nothing else has
changed.

The other pairs of the UTP are in use for a distance sensor
HC-SR04(measuring water level with an arduino)
When checking the wires i noticed that the resistance between 5V and 1wire
gnd for this cable was differt to the others: here its approx. 285kOhm.

anyone an idea how to solve this?

[Jan Kandziora]

Post by Jan Sennesael
The UTP is approximately 45m long, cat 5e. I am using wire nr 1/2 for
gnd/+5V and 4/5 for 1wire/gnd (hobbyboard pinout). The sensor worked without
problems on the tree setup (with a diy usb master), nothing else has
changed.
The other pairs of the UTP are in use for a distance sensor
HC-SR04(measuring water level with an arduino)
When checking the wires i noticed that the resistance between 5V and 1wire
gnd for this cable was differt to the others: here its approx. 285kOhm.
anyone an idea how to solve this?

Are you powering this HC-SR04 through the bus? If yes, how much current
does it draw? This current has to flow back through the GND wire and may
lift the GND level on the far end on long, thin GND wires an substantial
amount, creating communication problems.

Kind regards

Jan

[Jan Sennesael]

Post by Jan Kandziora
Are you powering this HC-SR04 through the bus? If yes, how much current

does it draw? This current has to flow back through the GND wire and >may
lift the GND level on the far end on long, thin GND wires an substantial
amount, creating communication problems.

Post by Jan Kandziora
Kind regards
Jan

The HC-SR04 is completely independent, it just uses the "free" wires on the
cat5e cable. The 1-wire bus gets it power from a seperate 5V adapter. The
HC-SR05 gets it power from a usb port of a hub.
I tried connecting the sensor to my old usb master, and there it works
without any problems, so i am leaving it like that for now. Just wondering
why its not working on the DS2482-800...
Greeting
Jan

[Michael Markstaller]

Well,

during seven years of usage/testing, I found the DS248x I2C-busmasters
to be the weakest available, especially with long wires..
Therefore I can only recommend to not use them outside a breadboard, a
DS2490/9490 (and many others) do perform much better;

Thats also the reason why I really don't understand they get used and
even recommended again and again (see RPi) although anybody familiar
with this should know: they just don't work very good..

Michael