Sending SPI over 25ft cable in noisy environment.

[JMG]

I need to send SPI data from a PIC to a digital pot in an industrial setting where there is all kinds of noise. The cables, up to 25ft long, also have to be routed close to a bank of switching PSU's.

I'm looking for recommendations on line drivers that will provide a pretty stout solution. Any suggestions or experiences?

Thanks.

 

[embpic]

Normally protocols like i2c, spi are work very well on single board.
If you wanna try long distance then use rs485 which work condition you show.

 

[JMG]

I understand what you are saying. If I could solve the issue by still using spi I'd prefer it though, but I will look in to RS485.

I was considering a buffer on each I/O to drive the lines harder. Speed is slow-ish at 1mbit max.

 

[ads-ee]

Why not run LVDS SPI down the line, especially if you were already planning to add a buffer to drive it. SPI only requires 4 lines so it will only require 4 pairs, which would conveniently fit in a CAT5 cable. And as they are differential twisted pair lines they will have more immunity to the noisy environment you mentioned as that will be common mode noise. Though you might have to build an interface module for the digital port if it only accepts single ended SPI.

You might want to read about some testing that has been done with LVDS over CAT5. https://www.ti.com/lit/an/slyt197/slyt197.pdf


Regards

 

[123jack]

As my granny used to say - horses for courses... I'd heed embpic if I were you.
You'll not only create work for yourself but end up re-inventing wheels if you don't.

 

[embpic]

ok you use SPI protocol which require 3/4 wire to send data but RS-485 also require 3-wires no matter you will require RS-485 translator.
and as you mention the environment as noisy then from my opinion if there is differential kinda data line then there will be more chances of
data Tx/Rx successful. Then it could be RS-485 or any other protocol require differential data lines.

 

[JMG]

DS9638 for RS422 looks perfect. Under $1 vs something like LTC1689CS for RS485 at $5.

 

[123jack]

As long as you understand "why" one costs 5 times more than the other and you know the cheaper solution will work
in your application there's nothing wrong with it. The trick of course is the "knowing" bit...