[sdiy] Opinions on input protection

[George Hearn]

For CMOS I usually just use a resistor in series with the input to limit the
internal protection diode current.  For TTL inputs I use a diode clamp to
+5V/0V and a resistor after the clamp in series with the input for
additional protection.  For inverting opamps I use a pair of anti-parallel
diodes from the (-) input to ground, with the input resistor (Rin) limiting
the fault current.  This is just my way of doing things, not necessarily the
correct (or best) way to protect, others may differ but it works for me.  G

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Joe Grisso
Sent: 26 March 2009 13:13
To: synth-Diy diy
Subject: [sdiy] Opinions on input protection

Hey all,

     I've been thinking a lot about how to interface general trigger
and gate signals into interior digital logic, and wanted to get some
opinions from the group. This specifically applies to when you're
taking an external binary signal (0/5V, etc) and sending it into a 5V
or 3.3V micro. There are many methods of input protection including
suppression diodes, using a transistor as a switch, or even just
running the input into a logic buffer and using the internal
protection circuit of the IC to shift the 0-10V gate/trig signal down
to something the processor can digest without committing seppuku. I've
seen each of these methods used, either alone or together in some
larger configuration. What does everyone prefer here?

Best,

-- 
Joe Grisso
Detachment 3 Engineering
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