Re: Connection of hardware

["Matt Shaver" <mshaver-at-erols.com>]

> From: Ray Henry <rehenry-at-up.net>
> I'm not convinced that you need opto isolation on the quadrature 
> input to the stg board.  I'd use isolation on all the input signals.  And
> use sockets so that I could replace smoked isolators.  
>   
> If the outputs went to an NPN transistor and pulled a relay near the stg, 
> I don't think I'd bother there either -- just use the relay to isolate
> power and load.
> 
> Jon E. had some breakout boards.  We really should work up a general
> purpose stg interface board plan and get some made up for all the signals.

I use the Opto22 stuff for I/O level translation (5VdcTTL/24Vdc/110Vac)
mainly. For things like limit switches where I have dry contacts to work
with, I've done this with no problem:

(PC_ground) - (N/O_switch) - (LPT_port_pin) - (100/1000ohm_resistor) -
(PC5Volts)

Shielding helps, and keep these kind of circuits away from big motors (and
their cables) and as short as practical. If the circuit had to be 100 feet
long, then you might worry, also a problem if the circuit connects things
like this where two things that don't share a common ground are connected:

(Wall|=Plug) - (PC) --------------200feet---------------- (Machine) -
(Plug=|Wall)

Matt