Looking at the data sheet for the Major League connectors called out
for in the SRM (A4.0.4) it calls for a stacking connector pin length
of 0.125 inches. I'm not sure what this is based on. The connector
data sheet says the contact point inside the connector is 0.079 inches
from the top of the connector. This allows only 0.042 inches for the
cape board thickness. Using the standard 0.062 inches for the cape
PCB thickness and you get 0.141 pin length minimum just to mate the
two boards. I don't know if there are any height restrictions because
I haven't looked at other manufacturers but using Major League
stacking connectors the shortest pin that fits the socket is 0.190
inches giving a stacking height of 0.275 to 0.446 inches center to
Should this be changed in the manual? Better yet, wouldn't a diagram
showing how the boards stack with dimensions would be useful. A spec
that has already covered this ground is the PC-104 document. They did
a pretty good job of resolving all the important issues and would be a
good model to follow.
I don’t plan to change it. The issue here is retention force. The shorter the pins the better because it makes it easier to remove a Cape from the BeagleBone. I picked this length based on the shortest standard pin I could get with it passing the point at which contact is made. Added length past the contact point does not add more contact coverage, it only makes it harder to remove because you have more pin to slide past the contacts. You can actually make the pins as long as you choose. There is no overall height restriction on a full Cape stack.
I can look at a diagram in the A6 version of the Manual. It is too late for the A5 manual.
I don't plan to change it. The issue here is retention force. The shorter the pins the better because it makes it easier to remove a Cape from the BeagleBone. I picked this length based on the shortest standard pin I could get with it passing the point at which contact is made. Added length past the contact point does not add more contact coverage, it only makes it harder to remove because you have more pin to slide past the contacts.
I can confirm that I like the short pins a lot more than the longer pins. the newer DVI capes are a joy to swap around, the prototype with long pins requires a *lot* of force.
We are not communicating. The issue is not retention force, the issue
is whether the pins are long enough to reach the BeagleBone socket.
Please read my post with an open mind. You will see what I am saying
if you read it carefully. Of course I may be wrong because this all
depends on the connector used on the BB and I can't find the BOM to
see exactly what is used.
According to the data sheet for the Major League SSHQ series (which is
what you call out in the SRM) the socket requires a MINIMUM insertion
of 0.079 to reach the point of initial contact. In addition to this,
the tails of the Cape connector have to go through the Cape PCB. If
you only allow 0.125 inches for the Cape tails (again what you call
out in the SRM) that only leaves 0.046 inches for the Cape PCB
thickness. And that doesn't insure good mating, you need to push the
end of the pins into the socket more than just touching the pin in the
The shortest pin tail you list in the SRM has 0.190 tails. This gives
a generous 0.111 inches for PCB thickness and insertion beyond the
initial point of contact. I'm not taking issue with this, just the
0.125 inches you specify as the minimum Cape tail length. It should
be the thickness of the PCB (depends on the Cape), plus 0.079 inches
plus a margin to allow proper mating of the connectors.
The bottom line is if someone uses the 0.125 inch Cape tail length and
picks a connector that gives just that length, their Cape will not
have enough pin protruding below the Cape to mate with the BB
Or do you use a different socket on the BeagleBone? Different
connector lines may have different mating distances.
My mind is not closed. But, I will take another look at this a soon as I can. I am busy trying to get A5 and A6 and a bunch of Capes out the door.
Oh, and the BOM is here and the PSB file includes your drill file. beaglebone_revC1_drill.zip
The files look good. Thanks.
Let me know if you need anything else.