i2c galvanic isolation

rickman wrote:
> Tauno Voipio wrote:
> >
... snip ...
> >
> > The basic problem is the same: the bus is essentially an
> > open-drain bidirectional bus, but the available isolators are
> > unidirectional. You need to bridge both the clock and the data
> > line with two isloators each, one for each direction. To prvent
> > inventing an isolating flip-flop, the isolator has to
> > understand pretty deeply the bus protocol to select the
> > direction properly. The contention mechanisms in I2C make this
> > a challenging situation.
> 
> Depending on how the basic I2C controller is implemented, this is
> not a big deal.  If the I2C interface is totally within a chip,
> then it might be tricky.  But if the I2C interface is in a PLD or
> MCU where you can control the external interface, then it is a
> slam dunk.  All you need is access to the open drain driver (I am
> finally getting used to not calling it "open collector"...).  You
> substitute the OptoIsolator for the OD driver and add a second OI
> for the receive (on a separate MCU/PLD pin) and you are done!
> 
> The only electrical issue I see is that it would take a wopping
> pullup to supply a bunch of OI with current, so I expect you
> would need access to the bus Vcc (or is it Vdd?) and wire the OI
> inputs as pullups.  Then the active OI output would connect the
> bus to ground to draw current through the OIs.  This may require
> a lot more current than the bus is normally designed for.  But
> that should be a good thing since it will speed up the
> transitions (unless you are worried about the EMI).  Of course
> you could add a transistor driver to reduce the loading, but you
> still need a common Vcc to drive the bus side of the OI and
> transistor.

Simplify :-)  You want a one wire path that detects collisions,
can be 'wire or' connected, opto-isolated, etc.  Go back further
than open collectors and, presto: Current loop.  Think mark/space.

I have driven 20 mA current loops, opto-isolated, through
literally miles of extremely noisy environments, surrounded by
elevators, diathermy, x-rays, you name it.

-- 
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
   <http://cbfalconer.home.att.net>  USE worldnet address!

Tauno Voipio <tauno.voipio@iki.fi.spambait_remove.invalid> wrote:

> "Henry" <otc_friend@gmx.net> wrote in message
> news:3fe373ce_1@news.arcor-ip.de...
>> Hi!
>> I need a i2c bus isolation with optocouplers or another technology. Google
>> doesn't know interesting hits. Any hints other than the Philips solution
>> with i2c bus drivers and optocouplers? An integrated solution as a cheap
>> sockable DIP or SMD device would be great.
>> I wonder that none of the big semiconductor producers is interested
>> producing such a device many people need. Hey marketing engineer, where
> are
>> you??
>> Greetings -
>> Henry

> Did you just ask for isolation of Maxim/Dallas single-wire bus?

> The basic problem is the same: the bus is essentially an open-drain
> bidirectional bus, but the available isolators are unidirectional. You need
> to bridge both the clock and the data line with two isloators each, one for
> each direction. To prvent inventing an isolating flip-flop, the isolator has
> to understand pretty deeply the bus protocol to select the direction
> properly. The contention mechanisms in I2C make this a challenging
> situation.

Take look at http://www.esacademy.com/faq/i2c/q_and_a/faq/i2cqa3.htm.
This circuit should do the job (although I haven't tested it).

j.

"Jacek R. Radzikowski" <jacek+maqmba@spamer.die.die.die.piranet.org> wrote
in message news:bs4ltb$mki$1@www.itl.waw.pl...
> Tauno Voipio <tauno.voipio@iki.fi.spambait_remove.invalid> wrote:
>
> > "Henry" <otc_friend@gmx.net> wrote in message
> > news:3fe373ce_1@news.arcor-ip.de...
> >> Hi!
> >> I need a i2c bus isolation with optocouplers or another technology.
Google
> >> doesn't know interesting hits. Any hints other than the Philips
solution
> >> with i2c bus drivers and optocouplers? An integrated solution as a
cheap
> >> sockable DIP or SMD device would be great.
> >> I wonder that none of the big semiconductor producers is interested
> >> producing such a device many people need. Hey marketing engineer, where
> > are
> >> you??
> >> Greetings -
> >> Henry
>
> > Did you just ask for isolation of Maxim/Dallas single-wire bus?
>
> > The basic problem is the same: the bus is essentially an open-drain
> > bidirectional bus, but the available isolators are unidirectional. You
need
> > to bridge both the clock and the data line with two isloators each, one
for
> > each direction. To prvent inventing an isolating flip-flop, the isolator
has
> > to understand pretty deeply the bus protocol to select the direction
> > properly. The contention mechanisms in I2C make this a challenging
> > situation.
>
> Take look at http://www.esacademy.com/faq/i2c/q_and_a/faq/i2cqa3.htm.
> This circuit should do the job (although I haven't tested it).
>

Did you notice that there is a severe speed restriction?

The circuit does not go over 10 kHz, but the bus is 100 kHz or faster.

Tauno Voipio
tauno voipio @ iki fi

Tauno Voipio wrote:
> 
> "Jacek R. Radzikowski" <jacek+maqmba@spamer.die.die.die.piranet.org> wrote
> in message news:bs4ltb$mki$1@www.itl.waw.pl...
> > Tauno Voipio <tauno.voipio@iki.fi.spambait_remove.invalid> wrote:
> >
> > > "Henry" <otc_friend@gmx.net> wrote in message
> > > news:3fe373ce_1@news.arcor-ip.de...
> > >> Hi!
> > >> I need a i2c bus isolation with optocouplers or another technology.
> Google
> > >> doesn't know interesting hits. Any hints other than the Philips
> solution
> > >> with i2c bus drivers and optocouplers? An integrated solution as a
> cheap
> > >> sockable DIP or SMD device would be great.
> > >> I wonder that none of the big semiconductor producers is interested
> > >> producing such a device many people need. Hey marketing engineer, where
> > > are
> > >> you??
> > >> Greetings -
> > >> Henry
> >
> > > Did you just ask for isolation of Maxim/Dallas single-wire bus?
> >
> > > The basic problem is the same: the bus is essentially an open-drain
> > > bidirectional bus, but the available isolators are unidirectional. You
> need
> > > to bridge both the clock and the data line with two isloators each, one
> for
> > > each direction. To prvent inventing an isolating flip-flop, the isolator
> has
> > > to understand pretty deeply the bus protocol to select the direction
> > > properly. The contention mechanisms in I2C make this a challenging
> > > situation.
> >
> > Take look at http://www.esacademy.com/faq/i2c/q_and_a/faq/i2cqa3.htm.
> > This circuit should do the job (although I haven't tested it).
> >
> 
> Did you notice that there is a severe speed restriction?
> 
> The circuit does not go over 10 kHz, but the bus is 100 kHz or faster.

I don't see any obvious reason why this circuit won't work at higher
speeds than 10kHz.  But I do see a problem which would result in a
glitch when both sides are driving the bus and one side releases.  As
the released side rises, it has to reach a voltage of around 3.4 volts
before the opto cuts off enough to let the other side turn on to drive
back.  This will be a short glitch and it is likely that the side doing
the release will not be watching.  But if any transactions are edge
detected, this is likely to cause a false edge.  Perhaps this has
something to do with the speed limitation?  

-- 

Rick "rickman" Collins

rick.collins@XYarius.com
Ignore the reply address. To email me use the above address with the XY
removed.

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design      URL http://www.arius.com
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We speak about i2c ! Having the benefit of directly interface to a mass of
different chips. Current loops is another field.

Surely.
The Philips 82B96 does isolation for i2c with a little help. What you
describe is more like Ethernet or other "networks".
You can directly add chips to the bus and that is the benefit of i2c.

Hi!
I feel a strong need for a i2c newsgroup, webpage or yahoo group. Exists?
All the webpages I know a very limited in parts to the subject i2c.

82B96 background info from Philips is here (interesting as they show other
vendors circuits and historical info)
http://my.semiconductors.philips.com/acrobat/other/mcu/notes_82b96.pdf
Yes, I think the 82B96 doesn't know anything about the protocol. As I
understand it the device works by sensing a differential voltage between
external and internal signal. The Philips block diagram shows voltage
sources of 0.6 volts in-line (= diodes?).

I didn't notice any further discussion to the subject but would like that!!
Hopefully it goes on ...

Henry <otc_friend@gmx.net> wrote:
> I didn't notice any further discussion to the subject but would like that!!

Ask new question, then ;-)  The old ones seem to be considered settled
by everybody else.

-- 
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Difficult to ask a unknown question :)