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

[JWBarlow at aol.com]

Paul (anyone?),

I'd really be interested in seeing the transistor buffer you mention. I'm in 
the same position of needing to limit some inputs (between 0V to 5V) so I'd 
like to see some options like the one you mention.

Thanks!
John B.

In a message dated 5/12/2003 1:27:25 AM Pacific Daylight Time, 
P.Maddox at signal.qinetiq.com writes:

> >The maximum voltage allowed on the inputs of
> >the microcontroller is 14 volts.
> 
> yeah but I bet thats not continous, I bet thats only instantaneous!
> 
> >* If a microcontroller I/O pin is configured for input, an incoming
> voltage
> >signal doesn't peak over 14 volts
> 
> several methods..
> 1)I would use a small resistor in series with the input pin (say 500Ohm) 
> and
> a zener diode (ideally the same voltage as your micro runs off, for example
> 5v1 for a 5V micro) this will stop things going above 5.1v, and
> below -0.7v..
> 2) diodes attached to both supplies (like crow says)
> 3) If you know what level the voltages are, use a dividing network, for
> example, if they are always going to be 0v -> +15v, use a 2K and 1K 
> resistor
> to give you a swing from 0v -> 5V...
> 
> >* If the microcontroller I/O pin is configured for output, it still works.
> >(The output will always be 5Vfrom the microcontroller.)
> 
> use a transistor to buffer the output, this way you can get the output to 
> go
> between 0v and +15v if you want, or by using scaling resistors, again you
> can choose what you want 0v -> 7.5v for example.
> 
> Paul

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