[TriEmbed] I2C Range Extension - It Works!

[Charles West]

Hey Chip,

Thanks for taking the time to try it.  We just ordered the PCBs (without
I2C buffering) for the CANInstall/I2CPotential project, so we don't really
have much data yet.

I look forward to looking at your designs (and hopefully talking next
week?).

Thanks,
Charlie

On Tue, Oct 6, 2015 at 9:22 PM, Charles McClelland <chip at mcclellands.org>
wrote:

> Charlie,
>
> Well, I tried it - but it did not work.  You can have multiple i2c devices
> on either end of the buffered line and can connect multiple buffered lines
> but there has to be one of these TI chips between the buffered lines and
> the i2c bus.
>
> I plan on keeping the daughter cards as small and simple as possible (less
> than 1 sq. in and less than $5).  At a minimum, there is the SOIC-8 chip
> and a couple resistors.  However, I need to decide if any polarity
> protection or other safeties are needed.  Any advice is appreciated.
>
> I will send out some designs for comment soon and document the project as
> well.  I hope this helps.
>
> Thanks,
>
> Chip
>
> On Oct 5, 2015, at 7:19 PM, Charles West <crwest at ncsu.edu> wrote:
>
> Hey Chip,
>
> If I may ask, have you tried using that chip just on one side?  With the
> I2CPotential/CANInstall project, it would be practical to stick one of
> those chips every 4-5 hub pieces but not on every one of the sensors.  If
> it is not too much trouble, it would be really nice to know what sort of
> range that configuration could get.
>
> Thanks,
> Charlie
>
> P.S.
>
> I would also be interested in hearing more about the daughter boards.
>
>
>
>
> On Mon, Oct 5, 2015 at 4:32 PM, pete at soper.us <triembed at triembed.org>
> wrote:
>
>> Preface: When I said earlier that with 26 gauge wire "the voltage drop is
>> spectacular" it was in the context of "powering a Raspberry Pi" current
>> levels. I'm pointing this out for others (same as on Friday to be sure
>> nobody was going to jumper their RPI ethernet connector to the supply
>> connection thinking the would just put "the right voltage into the other
>> end"). You're running just a few ma, of course.
>>
>> As far as there being a hazard to semiconductor junctions connected to a
>> 100 ft cable and ditto for something 10 ft above the dirt at Umstead Park,
>> I'm sorry to say yes, absolutely. Three items to start thinking about:
>>  Shielding
>>  Effective grounding
>>  Isolation
>> (I'm out of town w nothing but my phone, so I have to be brief).
>> Pete
>>
>>
>> ----- Reply message -----
>> From: "Charles McClelland via TriEmbed" <triembed at triembed.org>
>> To: <triembed at triembed.org>
>> Subject: [TriEmbed] I2C Range Extension - It Works!
>> Date: Mon, Oct 5, 2015 2:31 PM
>>
>> To all,
>>
>> Well, I got the $2 TI chip <http://www.ti.com/lit/ds/symlink/p82b715.pdf> in
>> and did a little experiment.  You can see what my set up looks like here
>> <https://www.dropbox.com/s/5umwqxaqp6619np/IMG_5409.jpg?dl=0>.  I was
>> able to get I2c working at 100KHz & 3.3V over 100’ of Cat 6 patch cable
>> which cost me less than $20.  I used the twisted pairs as follows -
>> SCL/GND, SDA / VCC - the interrupt lines don’t go through the TI chips but
>> they have no problem talking over 100’.
>>
>> Next step is to create some small “daughter cards” that I can put between
>> my micro controller and the i2C sensors - please let me know if you are
>> interested.  I will bring the setup to our next meeting.
>>
>> So, here is my next question, if this cable is running in a shallow
>> trench (6’) across the woods between my sensor and the cellular data
>> logger, do I need to worry about lightning?  What about the solar panel
>> which is 10’ up in the tree?  I had not thought much about this until
>> someone mentioned it in this thread and I have until Spring to figure this
>> out (hoping we are past Thunderstorms for the year).  Here is a picture
>> <http://www.seeinsights.com/projects/> and live feed from the sensor in
>> Lake Crabtree park.
>>
>>
>> On Oct 2, 2015, at 10:25 AM, triembed-request at triembed.org wrote:
>>
>> Send TriEmbed mailing list submissions to
>> triembed at triembed.org
>>
>> To subscribe or unsubscribe via the World Wide Web, visit
>> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
>> or, via email, send a message with subject or body 'help' to
>> triembed-request at triembed.org
>>
>> You can reach the person managing the list at
>> triembed-owner at triembed.org
>>
>> When replying, please edit your Subject line so it is more specific
>> than "Re: Contents of TriEmbed digest..."
>>
>>
>> Today's Topics:
>>
>>   1. Re: I2C range extension (Pete Soper)
>>   2. Re: I2C range extension (Grawburg)
>>   3. Re: I2C range extension (Carl Nobile)
>>   4. Re: I2C range extension (Pete Soper)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Fri, 02 Oct 2015 09:30:28 -0400
>> From: Pete Soper <pete at soper.us>
>> To: Carl Nobile <carl.nobile at gmail.com>
>> Cc: TriEmbed <triembed at triembed.org>
>> Subject: Re: [TriEmbed] I2C range extension
>> Message-ID: <560E86F4.8050102 at soper.us>
>> Content-Type: text/plain; charset="utf-8"; Format="flowed"
>>
>> Thanks for the correction. So 300ma through each of the two
>> power-carrying pairs. But if we recall Brian's Ohm's Law talk and look
>> at the voltage drop across 26 gauge wires we see where the limit really
>> comes from. The voltage drop is spectacular for even a few dozen feet.
>>
>> -Pete
>>
>> On 10/02/2015 09:06 AM, Carl Nobile wrote:
>>
>> Pete,
>>
>> I just checked, there are two specs PoE and PoE+. The first one has a
>> maximum current of 300mA and the second one has a max of 600mA.
>> Obviously both are too low. Too bad, this was a good idea.
>>
>> ~Carl
>>
>>
>> On Fri, Oct 2, 2015 at 8:36 AM, Pete Soper via TriEmbed
>> <triembed at triembed.org <mailto:triembed at triembed.org>> wrote:
>>
>>    WIthout a switching converter on the other end the wrong order of
>>    magnitude of current is available:
>>
>>
>> https://en.wikipedia.org/wiki/Power_over_Ethernet#Power_capacity_limits
>>
>>    On 10/02/2015 07:02 AM, Jim Ray via TriEmbed wrote:
>>
>>
>>    Has anyone modified Raspberry Pi to use PoE for power? Using
>>    standard Ethernet to drive a communications sub system based on
>>    another Raspberry Pi that has the requisite i/o and processor
>>    makes a lot of sense to me.
>>
>>
>>
>>    -Pete
>>
>>    _______________________________________________
>>    Triangle, NC Embedded Computing mailing list
>>    TriEmbed at triembed.org <mailto:TriEmbed at triembed.org>
>>    http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
>>    TriEmbed web site: http://TriEmbed.org <http://triembed.org/>
>>
>>
>>
>>
>> --
>>
>> -------------------------------------------------------------------------------
>> Carl J. Nobile (Software Engineer)
>> carl.nobile at gmail.com <mailto:carl.nobile at gmail.com>
>>
>> -------------------------------------------------------------------------------
>>
>>
>> -------------- next part --------------
>> An HTML attachment was scrubbed...
>> URL: <
>> http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151002/c9613eee/attachment-0001.html
>> >
>>
>> ------------------------------
>>
>> Message: 2
>> Date: Fri, 02 Oct 2015 09:33:08 -0400
>> From: Grawburg <grawburg at myglnc.com>
>> To: triembed at triembed.org
>> Subject: Re: [TriEmbed] I2C range extension
>> Message-ID: <a3b8ce46bdcb57844f7fe18fafc8aed5 at myglnc.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Since human hands must still plug/unplug RJ-type connectors there is a
>> practical limitation as to how small they can be.? I'd hate to have to use
>> a pair of tweezers and a magnifying head piece to plug my ethernet cable
>> into a Pi or my desktop.? Size does matter. And, the older I get the less
>> dexterity I have.
>>
>> Brian Grawburg
>>
>>
>> -----Original Message-----
>> From: "John Vaughters via TriEmbed" <triembed at triembed.org>
>> To: "Pete Soper" <pete at soper.us>, triembed at triembed.org
>> Date: 10/02/15 09:06 AM
>> Subject: Re: [TriEmbed] I2C range extension
>>
>> ?One thing that bothers the heck out of me is if you look at the Pi, What
>> is the largest component on the device? The GIANT RJ45 connector. How in
>> this world where every thing has shrunk have we (as in the technical
>> community) allowed this gross misuse of size with only a few wires be
>> soooooo large?
>>
>>
>> Why haven't we shrunk the ethernet connectors like everything else?
>>
>>
>>
>>
>>
>>
>>
>> -------------- next part --------------
>> An HTML attachment was scrubbed...
>> URL: <
>> http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151002/4aa45019/attachment-0001.html
>> >
>>
>> ------------------------------
>>
>> Message: 3
>> Date: Fri, 2 Oct 2015 09:49:59 -0400
>> From: Carl Nobile <carl.nobile at gmail.com>
>> To: Pete Soper <pete at soper.us>
>> Cc: TriEmbed <triembed at triembed.org>
>> Subject: Re: [TriEmbed] I2C range extension
>> Message-ID:
>> <CAGQqDQ+Ak_-HowBTCq0ZuTWJ1US+YB3u5jS=GjCrGMJZS5zidA at mail.gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Pete,
>>
>> I read the spec on Wikipedia
>> https://en.wikipedia.org/wiki/Power_over_Ethernet
>>
>> The spec is defined by power rating primarily. At the bottom of the page
>> it
>> shows current. It looks like these currents are minimal currents not
>> maximal. But, as you said, based on wire length and if power is held
>> steady
>> the wire resistance will kill the actual delivered current.
>>
>> ~Carl
>>
>>
>> On Fri, Oct 2, 2015 at 9:30 AM, Pete Soper <pete at soper.us> wrote:
>>
>> Thanks for the correction. So 300ma through each of the two power-carrying
>> pairs. But if we recall Brian's Ohm's Law talk and look at the voltage
>> drop
>> across 26 gauge wires we see where the limit really comes from. The
>> voltage
>> drop is spectacular for even a few dozen feet.
>>
>> -Pete
>>
>>
>> On 10/02/2015 09:06 AM, Carl Nobile wrote:
>>
>> Pete,
>>
>> I just checked, there are two specs PoE and PoE+. The first one has a
>> maximum current of 300mA and the second one has a max of 600mA. Obviously
>> both are too low. Too bad, this was a good idea.
>>
>> ~Carl
>>
>>
>> On Fri, Oct 2, 2015 at 8:36 AM, Pete Soper via TriEmbed <
>> triembed at triembed.org> wrote:
>>
>> WIthout a switching converter on the other end the wrong order of
>> magnitude of current is available:
>>
>>  https://en.wikipedia.org/wiki/Power_over_Ethernet#Power_capacity_limits
>>
>> On 10/02/2015 07:02 AM, Jim Ray via TriEmbed wrote:
>>
>> Has anyone modified Raspberry Pi to use PoE for power? Using standard
>> Ethernet to drive a communications sub system based on another Raspberry
>> Pi
>> that has the requisite i/o and processor makes a lot of sense to me.
>>
>>
>> -Pete
>>
>> _______________________________________________
>> Triangle, NC Embedded Computing mailing list
>> TriEmbed at triembed.org
>> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
>> TriEmbed web site: http://TriEmbed.org <http://triembed.org/>
>>
>>
>>
>>
>> --
>>
>>
>> -------------------------------------------------------------------------------
>> Carl J. Nobile (Software Engineer)
>> carl.nobile at gmail.com
>>
>>
>> -------------------------------------------------------------------------------
>>
>>
>>
>>
>>
>> --
>>
>> -------------------------------------------------------------------------------
>> Carl J. Nobile (Software Engineer)
>> carl.nobile at gmail.com
>>
>> -------------------------------------------------------------------------------
>> -------------- next part --------------
>> An HTML attachment was scrubbed...
>> URL: <
>> http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151002/37155d0a/attachment-0001.html
>> >
>>
>> ------------------------------
>>
>> Message: 4
>> Date: Fri, 02 Oct 2015 10:25:45 -0400
>> From: Pete Soper <pete at soper.us>
>> To: triembed at triembed.org
>> Subject: Re: [TriEmbed] I2C range extension
>> Message-ID: <560E93E9.5070906 at soper.us>
>> Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
>>
>> On 10/02/2015 09:33 AM, Grawburg via TriEmbed wrote:
>>
>> Since human hands must still plug/unplug RJ-type connectors there is a
>> practical limitation as to how small they can be.  I'd hate to have to
>> use a pair of tweezers and a magnifying head piece to plug my ethernet
>> cable into a Pi or my desktop.  Size does matter. And, the older I get
>> the less dexterity I have.
>>
>>
>> And where is the RadioShack needed for the adapters for those one room
>> school houses using RPIs in underdeveloped countries? It doesn't seem
>> mysterious why the Raspberry Pi folks use the most common, standard
>> connectors they can find (anybody else notice the main header matches
>> the old PC floppy disk drive signal cables?).
>>
>> But I agree 100% with John's point that it seems impossible that there
>> would be no modern alternative to the RJ45 after all this time. I'll bet
>> there are some amusing gossip stories about attempts to change this
>> situation.
>>
>> But going to the other extreme of build vs buy, the truth is that as
>> long as you can control impedance and deal with EMI if that's relevant
>> you can arrange your own connections. With amateur radio this is
>> standard operating procedure, most especially at high frequencies.
>>
>> -Pete
>>
>>
>> -------------- next part --------------
>> An HTML attachment was scrubbed...
>> URL: <
>> http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151002/385b5597/attachment.html
>> >
>>
>> ------------------------------
>>
>> Subject: Digest Footer
>>
>> _______________________________________________
>> TriEmbed mailing list
>> TriEmbed at triembed.org
>> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
>>
>>
>> ------------------------------
>>
>> End of TriEmbed Digest, Vol 29, Issue 10
>> ****************************************
>>
>>
>>
>> _______________________________________________
>> Triangle, NC Embedded Computing mailing list
>> TriEmbed at triembed.org
>> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
>> TriEmbed web site: http://TriEmbed.org <http://triembed.org/>
>>
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20151006/8c21d7be/attachment.htm>