[sdiy] VCLFO and VCADSR details available online

[Harry Bissell Jr]

If you can stand some series resistance...
protecting with shottky diodes to gaound and to
the positive supply can work well. The problem will be
that if the power supply is 'off' you can actually
power the circuit on with this configuration. 

Usually the pin will be protected to -.3V below ground
and +.3V above the positive supply... most chips can 
handle that

H^) harry




--- Adam Schabtach <adam at studionebula.com> wrote:

> 
> > I was originally trying to copy the CEM chips (and
> the Env 
> > Gen isn't a bad copy) and they were intended for
> programmable 
> > systems and include Level CV inputs.
> 
> I built an ADSR using Tom's schematic and source
> code. It's a dandy ADSR and
> the Scale and Exp/Lin controls make it more flexible
> than most analog EG
> designs. I didn't bring out the CV inputs to jacks
> but just used pots to
> supply variable voltages to the PIC inputs. 
> 
> One thing I've been wondering is whether anyone
> knows of a simple,
> low-parts-count protection circuit for
> microcontroller inputs. According to
> its data sheet, the PIC will be unhappy if you apply
> voltages to its inputs
> that are outside of the range [0, 5.1] or
> thereabouts. I have [-15, +15]
> present in my system and it would be unfortunate to
> zap the PIC by
> forgetting to be careful about what I plug into it.
> I used a zener diode and
> a regular diode to protect the Gate input on my
> ADSR, but (according to a
> SPICE model I tossed together) this configuration
> becomes less than linear
> as the input voltage approaches +5V. This is okay
> for the Gate input but
> would be somewhat problematic for CV inputs. I came
> up with a circuit that
> works well but it uses two op-amps. It seems like
> protecting the A/D inputs
> of micros must be a common-enough problem that
> someone has a simple
> solution, like maybe an off-the-shelf chip...?
> 
> --Adam
> 
>