[TriEmbed] I2C Range Extension - It Works!

Mon Oct 5 13:31:36 CDT 2015

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:
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> 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
>> 
>> 
>> 
>> 
>> -- 
>> -------------------------------------------------------------------------------
>> Carl J. Nobile (Software Engineer)
>> carl.nobile at gmail.com <mailto:carl.nobile at gmail.com>
>> -------------------------------------------------------------------------------
> 
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> ------------------------------
> 
> 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?
> 
> 
> 
> 
> 
> 
> 
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> ------------------------------
> 
> 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
>>> 
>>> 
>> 
>> 
>> --
>> 
>> -------------------------------------------------------------------------------
>> Carl J. Nobile (Software Engineer)
>> carl.nobile at gmail.com
>> 
>> -------------------------------------------------------------------------------
>> 
>> 
>> 
> 
> 
> -- 
> -------------------------------------------------------------------------------
> Carl J. Nobile (Software Engineer)
> carl.nobile at gmail.com
> -------------------------------------------------------------------------------
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> ------------------------------
> 
> 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
> 
> 
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