Is there anything that could be done to improve the driving capability
of the i2c devices ?

Out of interest is the DS2482-100 any better, it would of course be
possible have multiple ones of these on the same i2c bus.

Stuart


On 23/04/12 11:50, Achim Scheidl wrote:
> Don't forget, that the I²C bus-master can drive much less capacity load on
> cable (I measured a max of only 8,9nF which represent about 89m IY(ST)Y
> cable)
> The USB bus-master based with DS9490R is able to drive 28nF - so
> theoretically about 280m cable
>
> On Mon, Apr 23, 2012 at 11:25, Chris Lautre <chris.lau...@karusoft.com>wrote:
>
>> I would be very interested in a USB to 1Wire Hub with 8 1 Wire ports.
>> This would eb much better than using multiple  DS9490R.
>>
>> Chris
>>
>>
>> On 22/04/2012 10:42, Patryk wrote:
>>> I propose a new USB 1-wire adapter.
>>> The DS2490 native USB 1-wire adapter is no longer in production. I think
>>> you can still buy built adapters from Hobbyboards but if You want to
>> build
>>> your own it's nearly impossible to source this chip. The popular solution
>>> is to use DS2480B with some serial to USB converter like FT232 it behaves
>>> then like native DS2490.  However if one plans to have w big 1-wire
>>> network with multiple branches the better way seems be DS2482-800 which
>> is
>>> basically a 1-wire master with one bus  connected to a 8 port hub. You
>> can
>>> have then a star topology. Again You can still(not sure) buy a hub from
>>> Hobbyborad to achieve the same goal but the hub chip is also out of
>>> production. So if you are familiar with soldering iron this is a solution
>>> for you.
>>>
>>> The DS2482-800 uses I2C bus. The conversion form I2C to USB is handled by
>>> Atmega8A  which is a 8 bit microcontroller and runs a special program.
>>> It's a very popular chip it costs about $2(at least in Poland). However
>>> You have to upload the firmware to it for which you need a programmer. If
>>> you don't have one but you have an old PC with parallel port you can
>> build
>>> one with few resistors and a plug. Also Raspberry Pi can program AVR
>> chips.
>>> First I run i2c-tiny-usb
>>> http://www.harbaum.org/till/i2c_tiny_usb/index.shtml on Atmega8
>>> but there was a performance issue. The read from DS18B20 took about 3
>>> seconds
>>> and without specifying the bus about 10. Compared to 1.5 with DS2480 and
>>> similar
>>> time connected to vga i2c port.
>>> Fortunately there is a derivative project from Till's i2-usb-tiny it's
>>> called OSFI(Open Source InterFace) . It's part of a project called
>>> OpenServo http://www.openservo.com/StepByStep
>>> It uses Atemga8 and has better performance because it uses some built in
>>> i2c(do not know exactly).
>>>
>>> Here is the whole circuit. I think it's pretty explanatory. For testing
>>> You can omit the voltage regulator and power it directly from USB and not
>>> using the diodes should be fine for most computers. I done my prototype
>> on
>>> a breadboard and it works fine.
>>> http://ubuntuone.com/6uM1yQRB36zgGEFDxrTc7c
>>>
>>>
>>> On the 1-wire side DS9503 are not essential to get it running they just
>>> protect the bus from electrostatic discharges. However they are cheap. I
>>> used RJ-12 connectors (telephone) There are different standard's of
>> wiring
>>> the additional +5V the RJ45 are also popular. You can use screw
>> connectors
>>> as well. I think I will use 4 RJ45 for longer cables and if more power is
>>> needed and  RJ12 for thermometers.
>>>
>>> After assembling it on a breadboard You have to program the uC the
>>> firmware can be downloaded from OpenServo cvs.
>>>
>> http://www.openservo.com/viewcvs/OpenServo/Interfaces/OpenServo_InterFace/driver/Version_2/firmware/?root=cvs
>>> You need main.hex
>>> avrdude -c usbasp -p atmega8 -U lfuse:w:0x9f:m -U hfuse:w:0xc9:m -U
>>> flash:w:main.hex
>>>
>>> Then you can test if it's recognized by the system
>>> lsusb shows
>>> Bus 001 Device 005: ID 1964:0001
>>> There is no name for it
>>>
>>> Then you have to compile kernel module
>>>
>> http://www.openservo.com/viewcvs/OpenServo/Interfaces/OpenServo_InterFace/driver/Version_2/kernel/?root=cvs
>>> make
>>> sudo make install
>>> sudo depmod -a
>>>
>>> sudo modprobe osif
>>>
>>> sudo modprobe i2c-dev
>>>
>>> then
>>> sudo i2cdetect -l
>>> should show something like this
>>> i2c-0 i2c             OSIF at bus 001 device 005              I2C adapter
>>>
>>> Then you can run owfs
>>> sudo owfs –i2c=/dev/i2c-0 /mnt/owfs
>>> You can also use the parameter
>>> --i2c=ALL:ALL  and owfs will look at every i2c device. However there is
>>> some bug in older version an you might get segmentation fault. It is now
>>> fixed in CVS
>>>
>>> The you should get something like this
>>> sudo ls /mnt/owfs
>>> bus.0
>>> bus.1
>>> bus.2
>>> bus.3
>>> bus.4
>>> bus.5
>>> bus.6
>>> bus.7
>>> settings
>>> structure
>>> uncached
>>> statistics
>>> system
>>>
>>> Here's the whole Eagle project the board is half done
>>> http://ubuntuone.com/32tUJtqRyNr3ngTsApwW83
>>> and how it looks like on a breadboard
>>> http://ubuntuone.com/0CUuACUSJMW69aK2FznM6i
>>>
>>>
>>> Pleas give tips how to improve this tutorial. The board is on the way.
>>>
>>
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>
>
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