i2c almost working for me, was Re: i2c still not working for me

[Ian Lepore]

On Fri, 2019-04-19 at 10:20 +0300, Daniel Braniss wrote:
> > 
> > You can often compensate for a too-long cable by adding some stronger
> > pullups.  It's typical for a SOM to have pullups in the 4.7K range on
> > i2c.  You can add your own 1K pullups to see if that helps the rise
> > times on the bus.
> 
> well, at the moment it works ok with a 6m cable, i’ll try your suggestion soon.

Wow, I'm surprised that works; when you said "long" I was thinking
something like 1m.  You might need some sort of active helper device,
something like a TI txs0104e that has rise-time accellerators built in.
Or, maybe you could just slow the bus down enough to allow for the
rise/fall times on that big a capacitive load, like run the bus at 10
or 20khz instead of 100.

-- Ian