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A general purpose Flip Chip adapter board - Worth doing?

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    Originally posted by intabits View Post
    I still haven't checked whether ground (and power) pins are consistent across the various DEC bus systems, so the adapter does not assume anything in that regard.
    Good thinking. Ground and power pins are not consistent between Omnibus and Unibus backplanes. Not sure about Qbus, but I'd be surprised if it was.
    WTB: DEC PDP8-E rack header panels, AD8E, A008, A231, A232
    TA60, TM8-E, PC04, PRS01, BC80J, BC80M cable (RL8A cable)


      A couple of weeks ago, I had some of these adapters made by JLCPCB.
      As suggested by Roland, I didn't bother with the ENIG Gold fingers (and it would have near doubled the price).
      The boards are too short for the fab to do the beveling, so that must be done manually on some sandpaper.


      For anyone interested, these are the gerbers:

      I've also thought of another use for them - they could be used to make a "poor man's extender board", which might be desirable given the cost and difficulty of getting DEC style edge connector blocks.
      It uses one set of adapters to connect the Omnibus (or whatever) to ribbon cables that reach to above the surrounding boards, then pairs of adapters at the top end of the cables are used to sandwich the edge connector tabs of the DEC board under test (laying on some insulating material over the surrounding boards)

      Some sort of spacer would be needed between the two adapters to match the DEC board thickness, along with some fiddling to remove the black plastic strip on the headers that that join the adapters together, and receive the ribbon cable IDC connector.

      Perhaps bolts in the holes would be enough to make good contact between all the fingers, but some sort of clamp (wood or 3D printed?) over the fingers, with other bolts between the tabs would be better. This clamp would also keep the adapters aligned properly with the DEC board.

      Something like this:-


      It may even be better than an extender board in one respect: the board under test can be laying on something solid, rather than flapping around in the breeze, making it easier to probe and attach clip leads to.
      (Needs a lot of adapter boards though - 6 for a quad board, 9 for hex)
      Something to think about...
      Attached Files


        Here is my first attempt at a home-made Omnibus interface card using these adapters.

        It's a mash-up of the boot-loader designs by Malcolm Macleod and Roland Huisman, plus some extra stuff (power supply voltage monitoring, and provision to read the memory address and memory data buses)

        Yes, I do know about professional fab houses that are some or all of: cheaper, faster, easier, better. (I just had 5 different designs done that way a couple of weeks ago).
        But I want to explore the limits of what I can do at home, especially when my design may be total rubbish, so I don't want 5 expensive copies of a failure.
        It may also be easier to "bodge" on fixes with a DIY board (wider tracks & spacing, no solder mask or copper fills), which is desirable for development.

        Single sided PCBs are more practical for DIY, so that's what I did, using wire links on the "solder" side.
        That was the worst part of this project - next time I would try to do double sided.

        Being a DIY board, and single sided, I decided on surface mount because:-
        * Less holes to drill
        * No pins on the "solder" side, so wire links can run under components without interference.
        * Smaller components leave more space for traces.
        Even the through-hole style Arduino was mounted as an SMD.

        I used the "toner transfer" method, which went quite well:-


        As did the etching (I don't know why the forum software insists on rotating this one to vertical) :-


        Then came the drilling, this took about an hour:-

        The bottom rows are 1mm, most of the others are 0.8mm. I would have preferred 0.6mm, but all my bits of that size are now broken. Only one 0.8mm bit broke doing this, but probably more 0.6mm bits would have broken if I had any.


        Then the many wire links:-


        This took several hours, and I would not do this again. Next time I'll try double sided, and if that doesn't work, it's off to the fab...
        The 0.8mm holes are a bit too big for the via sizes used, so I'm expecting some problems with dodgy joints on some of these.

        Finally, all the parts soldered on:-
        Because it's single sided, the 40-pin adapter connectors are on the other side, so that the pins can be soldered on this side.
        I still need to make a couple of small 4-hole plates (probably from FR4) to bolt the board and adapters together.

        Glue used to keep the wire links from shorting:-


        Over the next weeks, I'll try to get this thing to do something useful...

        Attached Files


          What is the likelihood of removing the board and having the dual in line connectors separate leaving the edge connectors in the back plane?
          I have been a PDP-8 fan since the early 70s. My milk machine is a PDP-8/L w/4K core & an ASR-33. Paper Tape for storage. I have a PiDP-8/I, a PiDP-11/70 and a real live PDP-8/E. I"m always looking for more stuff for the PDP-8/E

          Looking to buy/acquire RX8E/RX28, RX01/RX02, TU56, TD8E, TC08, RK05, PC08, PC8E and any other PDP-8 equipment and boards.


            Originally posted by BitWiz View Post
            What is the likelihood of removing the board and having the dual in line connectors separate leaving the edge connectors in the back plane?

            Not shown in the last photo, I made small plates with 4 holes to join the board and adapters firmly together.
            An earlier photo in this thread shows my "dress rehearsal" mock-up using aluminium plates.

            I've added the plates (made of FR4) to the board above. It's shown in this thread:-

            It inserts and removes to the backplane as easily as any other board.
            Last edited by intabits; December 10, 2021, 01:59 PM.