I'd be interested if those who use PC104 actually use them throughout the satellite (i.e. they use them like Fox/Golf uses the QxN connectors where most of the signals pass through).  Also what board spacing where these connectors are used if there is anything typical.  (I think Eric said there were choices for the PC-104 connectors).
73,

Burns Fisher, WB1FJ
AMSAT(R) Engineering -- Flight Software


On Fri, Apr 7, 2023 at 10:26 AM Jonathan Brandenburg via pacsat-dev <pacsat-dev@amsat.org> wrote:
Following up on last night's conversation...

When there is talk about CubeSats using the PC-104 standard, what that
really means is the use of the PC-104 form factor in terms of board
size, mounting hole placement, and the 2x2x26 connector. CubeSats don't
adhere to any of the signalling or protocol aspects of PC-104 standards
(including additional connectors defined in the PC-104 standard).

There hasn't been any standards body define this form factor for
Cubesats (as far as I know) so I imagine it just sort of grew
organically from the first university satellites looking around for
something to copy and noticed the small form-factor computer.

As correctly noted, CubeSats don't standardize the use of the pins in
the PC-104 connector but it seems like component manufacturers looked
around to see how others had been using pins and followed suit. Thus if
PACSAT is using I2C, power, and ground pins there will be little
conflict. What I've seen is CubeSat component manufacturers offer an
option sheet that allows the customer to select from a set of options.
Along the lines of "put I2C pins here or there or do not connect" kind
of options.

I hear the comments about how "This a large connector!" and "How many
pins are really needed?" and "How are they used  by different
components?" All that is true. At same time it's also true that if
somebody is adding a component to their CubeSat it will most likely
expecting boards with the PC-104 form factor. AMSAT is an exception but
even then we had to partially adapt our boards to the PC-104 form factor
for use by non-AMSAT organizations.

When I'm at CubeSat Developers Workshop later this month, I'll do a
survey. While I will see at least one university eschew the PC-104 form
factor (because they're developing ALL the components in-house and
prefer a plug-in-slot configuration because it simplifies assembly a
lot) I expect most will have purchased the bus (including structure,
C&DH, EPS, and any ADCS) which will be in the PC-104 form factor. But I
could be surprised and the tide may be turning.

Comments?

Jonathan

--
Jonathan Brandenburg, KF5IDY


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