[TriEmbed] I2C range extension

[Rodney Radford]

I used I2C to control about a dozen salt water aquariums several years ago.

This involved a single PC bit-banging I2C out a parallel port (so was slow)
to a temperature sensor in each of the aquariums (some 30' away), sending
status out to a a couple 2x16 and 4x16 displays (I2C serial -> parallel ->
LCD parallel interface), and controlling the heaters.

This was for an outdoor, unheated, uninsulated building where the water in
the salt water aquariums had to be kept within a fairly narrow range.  We
monitored the temperature of the tanks and the external temp and would
start the heaters in the water when we notice the temp dropping.  This
replaced a mechanical temperature setup where the heaters would turn on
once the water got too cold, but by that time, the thermal mass of the
water prevented it from heating fast enough.

Now all of this would be replaced with a couple Arduinos, one devoted to
each tank, and a multi-drop serial bus to report back to the PC, but this
was back about 20 years ago.

This worked with no problems for the several years i worked with it.

A few things we did:
* twisted pair
* I2C range extenders with 12v pullups
* was not a noisy environment (outdoor building with only a single power
drop and no other electrical devices)

This was far enough back that you couldn't even buy the I2C devices in low
quantities, so companies like Pure Unobtanium sprung up (Ed Nisley's
company - previous author in Circuit Cellar Ink, and past Triangle Amateur
Robotics member) would buy parts in the minimum quantity and sell to
hobbyists.  Unfortunately by the time he would burn through enough stock to
break even, they would be available from other suppliers for less.

Also check out AccessBus - it was based on I2C and was designed to be a
desktop peripheral interface.  Unfortunately it was not adopted and USB has
since taken over this market.

So the short of it - yes, you can use I2C for longer distances in some
circumstances.


On Tue, Sep 29, 2015 at 10:03 PM, Charles West via TriEmbed <
triembed at triembed.org> wrote:

> Hello,
>
> Thanks again for all the good discussion on electrical connectors.
>
> We're still debating some of the specifics for the CANInstall and/or
> I2CPotential protocols.  One of the big things up in the air is how
> reliable I2C is and how long the range can be.
>
> My impression is that having a I2C bus of more than a meter or two is
> considered pushing your luck.  However, there seem to be range
> extender/repeater chips available that promise rather drastically improved
> range (such as the P82B715).
>
> If I may ask, what is the longest I2C bus you have built/seen?
>
> How has your experience been in terms of reliability?
>
> What sort of bus speeds do you tend to use?
>
> The bus speed is driven by the master, so theoretically you could have a
> sub-hertz baud rate?  Does this mean that you could get a really long range
> with a super slow baud rate or are the edges not sharp enough to be
> detected?
>
> Thanks,
> Charlie
>
> _______________________________________________
> 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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20150930/7393dd7e/attachment.htm>