Date   : Sun, 09 Jul 2006 16:23:41 +0800
From   : Thomas Drage <drage@...>
Subject: interfacing3

rather a flood of messages, I am sorry, but I tried a 3.3k resistor
between what I guessed to be ground and a data line, and sure enough the
Data B register changed from 255 to 191, so I guess I must be doing the
right thing.

How may I "safely" interface to it? Without breaking anything, esp. the
BBC's VIA chip, I want to detect when a voltage in the range of about 2V
appears. Can I put a transistors collector and emmitter into the
userport between a dataline and ground and connect my 2V logic to the
base?


Thinking something like the diagram below;


                10k
user port dataline -----/\/\/\-----|
                                   |
                                   |
                                   \C
                                    \
                                     |-B------/\/\/\------~2V logic
                                    /            3.3k
                                   /E
user port data ground ------------