Patrick,
You are correct about the PC104 issue. I brought this up early on in our project but people are use to referring to it as PC104. I read where the name PC104 is also copyright protected and there are some potential issues using this unless you pay them the license fee.
A part of this is how you number the pins. The LTM numbers them as a A and B group. I was having difficulty with that so I I numbered them 1 through 104. If you use the A and B method there is a change of getting the connector mixed up and as you are working on the board and flipping it over the A and B numbering is a challenge.
I found a particular Samtec Q series (PTHF-126-02-GF-Q-368) connector which had the correct configuration and put this on the BOM. This connector is available in a press fit version and a slip fit. The press fit is preferred because this means the pin holes will be a bit smaller giving more room for traces between the pins. Our vendor did not have a fixture to support the press fit so they soldered them in place with the connectors up off the board more than they should be. This is important later and will need to specified and controlled to support proper board stacking later. The fixture needed is a support block and a press block for an arbor press.
Attached is a drawing I made for the PCB fab and the subcontractor with a few dimension. This should match the LTM exactly. No one has verified any of this but we have boards that could be tested together if we had a board from another project.
Regarding the location of the 104 connector I followed Zack’s original layout work which I got off AMSAT GitHub. This should turn out to match other projects and boards.
Bob
On Aug 22, 2024, at 9:41 PM, Patrick Thomas via pacsat-dev <pacsat-dev@amsat.orgmailto:pacsat-dev@amsat.org> wrote:
Hi all,
First off, sorry I couldn't provide a better "customer experience" with solid answers on all the very on-point LTM questions tonight. I think it will definitely help to get an expert in to give a technical presentation and do some Q&A.
I did want to clarify one thing which may've been causing some confusion. We have been using the term "PC-104 connector," and if you search around for this online you will likely find the formal spechttps://pc104.org/wp-content/uploads/2015/02/PC104_Spec_v2_6.pdf (from pc104.orghttp://pc104.org) for the actual PC-104 connector, an ISA-derived 64 + 40 = 104-pin interface which looks like this: <09fFDU0WuGkm2PyW.png>
The cubesat community seems to use the term "PC-104 connector" to refer to the CubeSat Kit Bus (CSKB) connector, which is 26x4 = 104 pins (two 2x26 headers next to each other), which looks like this (top of the diagram, from the AMSAT LTM Brochure): <wvIuNHMbeUwkJ0qi.png>
I think this may have been the origin of some of the "it won't fit" or "the pinout isn't close" comments. Let me know if I'm on the right track.
I will be sure this is clear in the new LTM ICD.
As to where the connector is positioned, that is what I thought the Cal Poly cubesat design spec may have defined when I mentioned that in the meeting, but it looks like it had origins in Pumpkin, Inc. instead and then was more broadly adopted. I am going to do some further digging for a formal physical spec that I can point to. Meanwhile it should be easily derived from our layout files. (Or if someone on the list can answer, please speak up.)
Thanks,
Patrick
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