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Thread: Build your own PDP 8I, Part 4..

  1. #51
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    @ Marty - Hi, good to have you back in the 12-bit world! hope you're enjoying your wintery springtime in the Rockies (snow here today in Chicago).

    @ Daver2 - I'm definitely interested in one of your boards. There are a few other Prosser converts in the community who might well be interested. Thanks for the reminder about the LD12 archive - I had forgotten about it when the N8VEM project went quiet. I'm in no hurry for the boards - but I can see applying power to my own 8/I sometime in 2019 and it would be fun to play along on the LD12.

  2. #52
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    Wise words Jack - thanks.

    I was putting in some prototyping pads on the PCB last night and got to thinking:

    Do we want the PCB to have the VCC and GND tracks in (like the original) or just plain old holes for the IC sockets + various prototyping areas?

    I have already tracked the data and address lines for the RAM though - and will probably track the POWER pins on the P1 and P2 connectors.

    I am just trying to limit the PCB to what I am capable of delivering (i.e. putting loads of decoupling capacitors in and tracking the VCC/GND up may be beyond my capabilities at the moment). I was thinking of using wirewrapped IC sockets with the decoupling capacitors built in - and just wiring up the VCC/GND with red/black Kynar on a grid basis. I willl have a look at this again whilst I am sitting in the hotel tonight though to see if there is an easy way of tracking the power that even I can accomplish.

    I have put some 5 mm mounting holes around the edge of the PCB. A bit large? Possibly, but it is a large PCB...

    Dave

  3. #53
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    I think I may have answered my own question...

    I am going to make the PCB double sided (as the cost is identical if I went single sided)...

    If I put GND on the bottom copper and VCC on the top copper I can run GND/VCC down between each row of ICs - and 'grid them' under each IC. I can then put a single decoupling capacitor on each end of the row. I will put one decoupling capacitor for each separate RAM device though. This is 'fairly true' to the original.

    The constructor can then choose to use IC sockets with internal decoupling capacitors, solder their own decoupling capacitors onto each IC, or not bothering with decoupling capacitors at all.

    I will see how that pans out when I get back from my business trip.

    Dave

  4. #54
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    Hi all;

    Dave, Do You have any idea when or if You will get to the top Switch/Led plate PCB ??

    Just so I can get an idea of How to proceed..

    At Present, I an laying out the Wire-wrap Sockets, just to see what I can fit where..

    THANK YOU Marty

  5. #55
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    Nope...

    I would like to get the front panel done at some point though.

    Dave

  6. #56
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    Hi All;

    I am separating my various sizes of wire-wrap sockets into Coffee cans, from 14 pin thru 20 pin, and anything larger goes into one can..

    THANK YOU Marty

  7. #57
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    Hi All;

    All of the Sockets are in place, and I am starting the Power wiring (+5)..

    THANK YOU Marty

  8. #58
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    Hi All;

    The 555 Variable clock now works, which I didn't have before, before it was a fixed clock, and I changed Resistor values to change the frequency..

    Now, back to power wiring..

    THANK YOU Marty

  9. #59
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    Marty. The next part of the circuitry to construct is LD8 - converting the manual switch signals into CLRP, CONTP and SWONMAN (plus a few auxiliary signals).

    I have looked at the price and availability of wire-wrap sockets with in-built decoupling capacitors. Too expensive and in limited availability . I have gone back to the idea of incorporating 100nF MLCCs onto my PCB. I think I have found a way (I have tracked in the required capacitors for the L and M rows now). Fiddly, but doable. If I add them to the PCB layout, then constructors can choose to add them or not... I know what my Easter holidays will consist off now ...

    Dave

  10. #60
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    Hi All;

    Daver2, what I did was use larger IC wire-wrap sockets for the capacitor, so for a 14 pin IC I used a 16 pin socket, for a 16 pin IC I used an 18 pin socket.. I didn't do this for the 20 pin Sockets nor for the 24 pin socket.. On the 24 pin socket I can wire in the few caps that are needed..

    THANK YOU Marty

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