ComputerVoltageSources

--- In ComputerVoltageSources@yahoogroups.com, "Grant Richter" 
<grichter@...> wrote:
> Current plan is to support 8 in and 8 outs, both 10 volt and 5
> volt ranges with different resistors.
> 
> Unipolar output for simplicity and accuracy.

Can someone explain the current thinking on the input level and 
offset?  Will this allow me to drive the analog inputs with +/- 5 
volt signals?  Modulating inputs with LFOs is a reasonable 
application.  Accuracy isn't overly important for the programs I've 
written.
> 
> The only change I see is to move the start PB to IRQ1 input (which
> is now AUX). That would allow using an interupt service routine
> for the start PB.

Are you still trying for PSIM compatibility?  Personally I use the 
start and stop switches / inputs for modes more than start and 
stop.  I'm not too interested in being able to drive this via 
interrupts but I do want to be able to detect a narrow trigger.  As 
such I would prefer to keep the interrupt on aux.  Here's a couple 
of thoughts.  I have written code to detect edges on timer 
interupts.  This supports detection of the start, stop, or aux 
inputs.  The only requirement is that the pulse width needs to be 
greater than the interrupt period.  For my implementation that is 1 
mS or 10 mS.  This would be sufficient for switches or gates but not 
triggers.  The interrupt latency would be minor.  Another thought is 
to remap the three inputs that support IRQs for all three inputs.  
If you are going to change one and impact backwards compatibility, 
why not change all three?  I don't remember the specific pins but 
this would be a minor adjustment to existing code.

> That still leaves the I2C port uncommited. Does anyone have a neat 
I2C port expanded they would like to mention?

At this point I would terminate it in a connector for future 
expansion.  Let's get the basic design in the hands of users and 
they'll expand the system based on real needs rather than 
anticipation.

Dave