[sdiy] CV --> microcontroller, how to limit input voltage?

[Bret Truchan]

Sorry if this is a duplicate message.  I had huge trouble posting with my 
mailblocks account.  Maybe this will work better...

Hello!  
  
I have a newbie question for everyone! I'm creating a module that has 
a microcontroller on the back-end. It's supposed to be able to hook up to a 
Doepfer, Analog Solutions, Blacet, etc.  
  
The microcontroller has a bunch of I/O lines that are configurable as either 
inputs or outputs. I want to keep that flexibility. Some of the I/O lines 
COULD be configured as A/D converters, so I don't want to 
buffer these lines in any way that would force them into an +5/+0 
volt paradigm. The maximum voltage allowed on the inputs of 
the microcontroller is 14 volts.  
  
My question is, what type of circuit should I put on the I/O lines of the 
microcontroller to ensure that:  
  
* If a microcontroller I/O pin is configured for input, an incoming voltage 
signal doesn't peak over 14 volts  
* If the microcontroller I/O pin is configured for output, it still works. 
(The output will always be 5Vfrom the microcontroller.)  
  
Thanks a ton! If anyone has a schematic that could do this, that'd 
be great!!  
  
- Bret

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