ComputerVoltageSources

Dear Dave -

OK, I'm going to dive into this I2C thing headfirst without checking the
water depth  :)    The good news is I've built some CGS modules with
great success; but I still have very little understanding of what's
going on in the circuits...

I'm ordering an MCP23008 ($1.04 at mouser!) and want to try hooking up 8
toggle switches to it, and then on to P6/P7 on the PSIM;  the most
minimal setup possible so I can experiment.    If you have time for a
couple questions...


[voltage source] -->  toggle switch  -->  input pin of MCP23008
 a)  What should I use for the [voltage source], ie. what voltage ?   
(Is there somewhere on the PSIM I can pull this from?)


MCP23008  -->  P6
MCP23008  -->  P7
 b)  Which pins on the MCP go to P6/P7?
 c)  Do I need a resistor in between them?  (you mentioned a pullup
resistor)


Power/ground/other connections to the MCP23008
 d)  What other connections (minimal!) do I need to make?



I was looking at your I2C/RS-232 .jpg on your site, but that was with a
different chip.  And I've looked at the datasheets for the MCP that you
sent me, but for me the majority of info there might as well be in
Icelandic  :)

Any help you can provide would be great!
Thanks again,
Andrew


>>> "djbrow54" <davebr@...> 12/18/06 11:11 PM >>>
For additional digital inputs or outputs, you can expand the PSIM with 
I2C.  There is a two pin jack for P6 and P7 which can be used to 
expand the I/O.  I have an I2C to RS-232 and an I2C to MIDI that I 
use.  I have also tested the PSIM with an MCP23008 I2C to 8 bit port 
expander.  This will give you any combination of digital inputs and 
outputs.  This is what I plan on using to control the second DAC and 
programmable reference voltages on the CVS.  I used 5 of the 8 pins 
with 3 spare.  All you need is two pullup resistors and there is even 
room on the PSIM board to add these.  You can see my schematic for an 
I2C to RS-232 to drive the TTS-256/SpeakJet at
http://modularsynthesis.com/modules/synthmodules/PSIM-SpeakJet/PSIM-
speakjet.htm  (sorry - long link)

I have an AtomPro FAQ on my 
http://modularsynthesis.com/modules/synthmodules/synthmodules.htm
page.  The link is just above the programs.  Some of this is 
documented in there along with some timing information.  Reading 
digital inputs via I2C isn't that fast as you have a number of bytes 
for the transfer.  Outputs are pretty quick.

Lots of opportunities.  This is basically what the CVS design is with 
a second DAC for 8 analog outputs, MIDI, and programmable references 
so you can read 16 potentiometers.

However, we're stalled at the PCB layout.  I'm ready to give up and 
just hand wire my board.

Dave