Michael Rigby-Jones wrote:
> Do you have suggestion for a suitably sensitive opto-coupler?

Not off the top of my head.  Optocouplers with uncommited phototransistor
outputs are common though, so look around.

> I made
> an isolated I2C interface many years back with standard 4N36 devices
> and it was incredibly slow, it could barely manage 10kbit/s and then
> only with the LED current cranked well up.

Using two optos for separate low and high side drive helps speed things
considerably.  Phototransistors are slow to turn off because nothing is
draining the carriers from the base.  However, since the transistor current
is inherently limited and the other transistor is turning on, the overall
output level transition happens much quicker than with a single output and a
passive pullup.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist