I2C Wire Lenght for 7 digit display

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oakbarn
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I2C Wire Lenght for 7 digit display

Post by oakbarn »

OCCS suggested 3 feet or less. As I had started to mount my BCS someplace not in 3 feet of where I wand my external display I did five test:

BCS I2C PID Display Module (External 7 digit display)

This test involved running a length of wire and connecting it to the I2C PigTail from OCCS.
Test 1:
14 foot section of CAT5e shielded wire for GND, SCL and SDA.
14 Foot section 16 ga speaker wire for 12 vdc via X2 connector on back.
Results: No issues seen. Debug was on steady and responded to temperature changes.

Test 2:

14 foot section of CAT5e shielded wire for GND, SCL, SDA and 12vdc
Results: No issues seen. Debug was on steady and responded to temperature changes.


Test 3:
14 foot section of 16ga shielded wire for GND, SCL and SDA.
14 Foot section 16 ga speaker wire for 12 vdc via X2 connector on back.
Results: No issues seen. Debug was on steady and responded to temperature changes.

Test 4:
14 foot section of 16ga shielded wire for GND, SCL, SDA and 12vdc
Results: No issues seen. Debug was on steady and responded to temperature changes.

Test 5:
14 foot section of 16ga shielded wire and a 14 foot section of 16ga shielded wire for GND, SCL, SDA and 12vdc for a total of 28 feet.
Results: No issues seen. Debug was on steady and responded to temperature changes.

For me, looks like at least 28 feet or less will work between BCS and PID Display Module (External 7 digit display) :D
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Re: I2C Wire Lenght for 7 digit display

Post by JonW »

Don't complain if your system starts acting buggy or if your expansion port (I2C driver chip) gets fried.

I2C was created as a chip-to-chip communication - not an off board driver solution.
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Re: I2C Wire Lenght for 7 digit display

Post by lewdog50 »

here is an option for increasing the bus length safely

http://sandboxelectronics.com/?product= ... 715-module
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Re: I2C Wire Lenght for 7 digit display

Post by oakbarn »

JonW wrote:Don't complain if your system starts acting buggy or if your expansion port (I2C driver chip) gets fried.

I2C was created as a chip-to-chip communication - not an off board driver solution.
I based my test on the following that I found on the internet (along with a lot of stuff about long communications using I2C.)

Reliable I2C-bus communication at high data rates, and over many meters,
can be achieved using widely available twisted-pair communication cable
(e.g. Category 5e and similar 4-pair cables, as typically used for Ethernet
communications).
......
Differences in local ground potential between the cable ends of at least 5 V
(of either polarity, or ac peak) will not affect the data integrity.
High levels of ESD immunity can be achieved when required.

I can understand "buggy" but how would this fry the I2C communications?

I have ordered the -i2c-long-cable-extender-p82b715-module just to be safe.

Even that says “several meters” without the module in the overview of the product.
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Re: I2C Wire Lenght for 7 digit display

Post by oakbarn »

lewdog50 wrote:here is an option for increasing the bus length safely

http://sandboxelectronics.com/?product= ... 715-module
You need two of them. One on each end of the long wires.
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