On Tuesday, April 29, 2014 10:42:11 AM UTC-5, Frank Schieschke wrote:
how do you realize the function of the Pulldown transistor Q4 with your single voltage regulator?
Yes, you are correct, I must stop posting early in morning.
However, driving the big transistors with this scheme as a source of stable, no adjustment necessary 2.7 V is interesting rather than the variable resistor. There are other schemes to avoid the variable. Any way to eliminate moving parts or adjustments is usually a win.
Reason #2 not to post too early in morning is most LDOs are pretty picky about the ESR of the capacitance at their output if you want stability, so need a cap too.
Anyway I still want one card and I'm probably going to modify it into a "service" card for my 8-slot unterminated board. It'll always be plugged in, so anything it can do to make troubleshooting more convenient beyond just bus termination would be helpful. Cloning the ckts on the bus extender is an interesting idea.
In the long run as some kind of future version of both cards I wonder if you could combine both PCBs into one, and then populate as necessary to create an extender or a terminator depending on parts installed.