[sdiy] Modular synth input/output protection.

[Tim Parkhurst]

On 1/22/06, Rykhaard D.A.M.I.A.N. <rykhaard at gmail.com> wrote:
> This thread has given me an idea - that I'd like to know if anyone
> else has already taken care of?  (I'm having a hard time, trying to
> come up with a title for it.)
>
> My thought is - to collect the guidelines / parameters / cautions /
> etc., for safety in designing and building a module.  As Dave had
> asked - is there a way to protect a system's outputs from being hooked
> up to other outputs?  Is this something that we still have to worry
> about, these days, or are precautions built into the chips that we're
> building things around?  (Or, transistors for that matter - as they're
> quite often used for output buffers.)
>
snip...
>
> --
> Take care,
> Warmth and Peace,
> Ryk
>

Hey Ryk,

Here's an excerpt from Thomas Henry's Drum Cookbook. This section
talks about synth standards and is itself from Bernie Hutchin's
Electronotes:

*************************************************
CONTROL INPUTS
·Voltage:           0 to +5V
·Impedance:     100K Ohm
·Overvoltage and reverse voltage protected

AUDIO INPUTS
·Voltage:           ±5V
·Impedance:     100K Ohm
·100k attenuators on the inputs
·DC coupled where possible

AUDIO OUTPUTS
·Voltage:           ±5V
·Impedance:     1K Ohm
·DC coupled where possible
·Short circuit protected
******************************************

>From what I can see, the protections listed above are taken care of by
standard buffers on inputs and outputs, including 100k resistors on
inputs going into an op amp buffer, and 1k resistors on outputs
(usually coming from an op amp buffer). One place to watch out might
be digital I/O. This is where I would probably use a resistor, zener,
or schotky diodes to ground and +V (the digital supply).

Tim (enjoying a lazy Sunday morning) Servo
--
"Imagination is more important than knowledge." - Albert Einstein