I am considering linking some 20 Arduino Uno R3s with an I2C bus in very large facilities.
If I setup the TWI in series between Arduinos the total length may reach 2000 feet.
If I setup the TWI with a star configuration the maximum length could reach 400 feet.
I would use CAT5e wiring to power the Arduinos and to provice the I2C links.
Does anyone have experience with TWI interface lengths such as these?
How can I determine if this is reasonable?
Thanks in advance to all who participate.
You can determin if it is reasionable by the cable's capacitance. Check the data sheet of your devices for what capacitave load they can drive. However I can tell you now that 400 feet is way over the top, I think even for an I2C extender chip.
you might look for RS485,
see - http://www.maximintegrated.com/en/app-notes/index.mvp/id/3884 - (indication for speed /length)
Rob is right.. RS485 would be far better for this distance.
Some info and example HERE:
RS485-RS422 Overview HERE:
Example of connecting two Arduinos, with sample code ArduinoInfo.Info WIKI HERE:
A nice example of a protocol for multiple Arduino was written by Nick Gammom HERE:
Let us know how this goes..
Thank you for this info. Very grateful.
I will look into the examples, and report back with my test results.
P
After extensive learning and development, I can report that I have been very successful implementing the RS-485 recommendations. I used Nick Gammon's RS-485 non-blocking library with the mega register to sync transmissions.
I designed a Mega 2560 shield with an LTC485i chip and have connected up to 25 mega2560 using Cat6 23awg for power and RS-485 communication.
Its works great and flawlessly.
I will be testing longer distances and larger number of megas on the same bus.
Will test the limits.
Am very gratefull for this forum and the time you guys take to give new people like me advice.