I know, I can't fix everything. Detaching pin 40 shouldn't mess up users though. The pin will still be there, and still plugged into GND on the base board.


On 10 Dec 2015 15:57, "King, Lawrence" <lking@qti.qualcomm.com> wrote:
> Hi Grant:
> Another way to resolve the issue is to put a shroud around the pins so it physically can't go in off by one. The mechanical spec leaves a clearance around the connector explicitly for this. Unfortunately a shrouded version of the pass-through connector is not available. Adding the 60-pin connector to the bottom of the board would also provide mechanical keying.
> As with all of the hobby class stuff it is up to the user to ensure everything is plugged in correctly to prevent damage.
> How do you protect against off by one when it is an entire row off (up-down, instead of left-right)?
> As far as removing one ground, you will get away with it, but then the users will find a new way to blow up the card. This will also create grief when a user plugs a wire into the corner pin expecting it to be ground only to discover it isn't.
> Lawrence King  lking@qti.qualcomm.com
> Engineer, Sr. Staff/Manager
> Qualcomm Canada Inc.
> (905)482-5403 desk (x25403)
> (416)627-7302 cell
> -----Original Message-----
> From: glikely@secretlab.ca [mailto:glikely@secretlab.ca] On Behalf Of Grant Likely
> Sent: Thursday, December 10, 2015 6:26 AM
> To: George Grey <george.grey@linaro.org>; King, Lawrence <lking@qti.qualcomm.com>; Yang Zhang <yang.zhang@96boards.org>; mezzanine@lists.96boards.org; Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
> Subject: 96B-Grove change request for review
> I just made the following change to the Rev C schematic after someone blew up their board by connecting the Sensors board off-by-one.
> However,  I'm not entirely sure if it is a good idea. Full description below, but the jist is I disconnected pin 40 from GND to prevent +12V getting shorted to +5V. There are three other GND pins on the connector, pin 1, 2 & 39. Do you think having one GND pin on the right hand side of the connector provide a sufficient ground connection?
> g.
> Change description:
>     Protect baseboard if Sensors board is installed incorrectly
>     Disconnect pins 36 (PWR_IN) and 40 (GND) to protect the baseboard if P1
>     gets installed off-by-one. Keeping PWR_IN pins 36 and 38 tied together
>     will short +12V directly to GPIO_L (34) or GND (40) if the connector was
>     off by one. Having pin 40 attached to GND would cause +12V to be shorted
>     directly to the +5V rail. To protect the baseboard, remove these direct
>     connections. Using only one PWR_IN pin is more than sufficient for this
>     board because it isn't used for anything. There are also three other GND
>     pins on the connector rated at 2A each. Dropping one should not be an
>     issue.
>     These changes don't guarantee to protect the baseboard. 5V would still
>     get shunted to the 1.8V rail which may still destroy the board, but
>     there is at least a fighting chance of not frying something.
>     Things would be so much better if we had a keyed connector
>     Signed-off-by: Grant Likely <grant.likely@linaro.org>