beaglebone-black - Flipbook - Page 93
BeagleBone Black
operation of your board by exposing those signals for expansion. This con昀椀guration consists of a combination
of the stacking and nonstacking style connectors.
Fig. 8.8: Stacked w/Signal Stealing Expansion Connector
8.2.6 Retention Force
The length of the pins on the expansion header has a direct relationship to the amount of force that is used
to remove a cape from the BeagleBone Black. The longer the pins extend into the connector the harder it is
to remove. There is no rule that says that if longer pins are used, that the connector pins have to extend all
the way into the mating connector on the BeagleBone Black, but this is controlled by the user and therefore is
hard to control. We have also found that if you use gold pins, while more expensive, it makes for a smoother
昀椀nish which reduces the friction.
This section will attempt to describe the tradeo昀昀s and things to consider when selecting a connector and its
pin length.
Figure 69 shows the key measurements used in calculating how much the pin extends past the contact point
on the connector, what we call overhang.
Fig. 8.9: Connector Pin Insertion Depth
To calculate the amount of the pin that extends past the Point of Contact, use the following formula:
Overhang=Total Pin Length- PCB thickness (.062) - contact point (.079)
The longer the pin extends past the contact point, the more force it will take to insert and remove the board.
Removal is a greater issue than the insertion.
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Chapter 8. Cape Board Support
