On 9/13/2011 8:16 PM, Brent Brown wrote:
> Other:
> - Have opportunity now to modify daughter board design now before going t=
o full
> production, but seems would have to add an unreasonable amount of circuit=
ry to
> isolate during power up +3.3V, +5V, RXD and TXD.
> - Prefer not to re-design main board, even so I suspect it would not be t=
rivial to add
> comprehensive protection.
>
> For I'm going with 1 and 2 above, looking at the feasibility of 3. Keen t=
o hear any
> other ideas~!
   Add a zener diode on each of the 3.3V, +5V, RXD and TXD lines so it=20
clamps the voltage at whatever is safe for those pins. Put a 10K +=20
resistor across +12V power rails so that when the +12V battery power is=20
removed those capacitors self discharge quickly enough to prevent=20
someone from plugging in another board before they discharge normally. =20
Also consider adding an LED to the board near the connector that shows=20
when the board is powered to remind people when plugging in another board.

Good Luck
Mark

--=20
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