Build notes

[Chuck McManis]

First things GREAT JOB! I really enjoyed putting this together and its great fun to watch the blinking lights when it is running OS/8. I entered my favorite "Cylon" program (rotates a bit back and forth in the accumulator) and it works great.

To capture some thoughts about future projects and for folks who are thinking of doing something similar (I've half a mind to do a PDP 8/E version, I've got an 8/e, 8/f, and two 8/m's but don't run them often because of the noise and the heat they generate.) I've captured some thoughts I had while building the kit ...

By and large this thing went together as expected, there were some places where a note in the build instructions would have been helpful.

First is that the kit is not compatible with the older Model A or Model B Pi, you really have to have the B+ (or A+). You can also use a Pi2 which I ended up with as that was all the local shop had in stock. However, if you use a Pi2 the connectors for network and USB go RIGHT TO THE EDGE so you will end up cutting a big notch out of the case if you use a Pi 2 here.

The second is that the switches solder in with one set of lugs OFF the board. This wasn't clear to me and I was trying to figure out if I had the wrong switches or needed to bend out one of the lugs. Eventually I saw the alignment of the round holes with the switch tabs and that lead me to understand how the switches needed to hang off the edge.

Once constructed, there is no configuration which sits reasonably in the box. Even just the plexi doesn't sit in the box so I'm going to be building a new box (which was kind of necessitated anyway by the desire to actually connect a network cable to it).

I found painting both white and brown colors gave me a better look, the paint came from the hobby store from their model paint rack, I used Burnt Sienna and While (glossy). This is acrylic paint, drys to re-coat in about an hour, and drys hard in 24 hours. Sticks very well to plastic.

if you look closely you can see a couple of spacers on the top of the board (top picture). Those keep the plexi off the LEDs when the wooden box isn't there. Ideally I think I'll end up gluing them to the back side of the front panel, that way I can always insure the panel is in the same place with respect to the switches.

On the switches I found that I needed to trim the skewer down to about 2mm extending on each end, this allowes the plexi to rest on the switch mounts rather than on the skewer pole. In an effort to improve the opportunity to fit the board I'm going to trim off the lower switch mounts about half way through the mounting hole. As they are they stick out past the plex on the south end further hampering mounting it in the box.

I liked the way the Pi mounted (raised nylon spacers) but its positioning is not adjustable, I may end up building a short cable and put a small IDC cable between the front panel and the Pi. Also it might make sense to start with a Beaglebone Black as it has more I/O's and would not need the serial hack, but other than that I think the choice of the Pi is fine.

If you respin it, I would consider making it about 3mm larger all around. The PC board could accomodate the full switches at that point,and you could put mounting studs on the four corners of the plexi for stability and registration (alignment of the plexi to the LEDs and switches).

I would also consder making the front panel connect to the PI with an IDC cable, That would give you more flexibility with routing cables in the box. You might consider laying out a design for a laser cut box, that would be pretty easy to get made in a makerspace.

All in all its a great piece of work, and I've enjoyed it tremendously. And I'm glad my friend Mark spotted it :-).

--Chuck

[Obsolescence]

Chuck,

Thanks for the feedback! That is very useful for the next run. A couple of comments and questions --

 

if you use a Pi2 the connectors for network and USB go RIGHT TO THE EDGE so you will end up cutting a big notch out of the case if you use a Pi 2 here.

That was intentional - the idea was to make the connectors sit flush with the case so a oblong slot in the case would immediately face them. I did not want the Pi to stick out (so that the connectors actually go in to the wooden case) because it requires more precision from builders.
 

The second is that the switches solder in with one set of lugs OFF the board. This wasn't clear to me

Ah! I heard that from others too, I will add it to the Building Instructions page.

By the way, the reason that the 3rd, unused pin of each switch dangles off the board is simple cost control. The board is exactly 9.9 mm tall. Make it 10.4mm and the PCB manufacturer raises the cost quite a bit. I had to keep the size below 30 * 10cm.
 

Once constructed, there is no configuration which sits reasonably in the box. Even just the plexi doesn't sit in the box

That is a big thing, but I suspect (as I heard it from a few others) one of the two issues below is the solution:

Issue #1: fitting the plexi requires more force than you're comfortable with...
The dimension of wooden cases varies about 1mm in height and width. Fair enough, at the price I cannot really complain about that. Anyway, for most cases you have to really force the plexi into the case. The good thing: it then does not need screws. But often, when fitting the plexi it requires bending it a bit upwards in the middle, then the left and right edges can be wedged in. With some force.

I am sure all the cases fit the plexi because I mount the plexi into the case when I ship them out. But for some people, I have heard that putting the plexi back requires more force than they are comfortable with. Be sure though - the plexi will fit if you apply the force necessary and nothing will break. I tried each and every kit before shipping.

Another approach is to scrape 0.5 mm off the inner edges of the case with a Stanley knife. The soft bamboo scrapes off neatly. About 50% of PiDP cases have been 'scraped' by me to get a good fit actually.

Issue #2
One builder got confused about the positioning of the PCB+switches in the case. The metal mounts of the switches need to rest on the inner (recessed) side of the case. That positions the PCB perfectly versus the transparent LED windows in the plexi. Clipping the metal mounts off the switches will make positioning it much more tricky. At least, I think so :)

 

so I'm going to be building a new box (which was kind of necessitated anyway by the desire to actually connect a network cable to it).

It really should not be necessary. The panel was fitted in the case when I sent the kits out, so I know for sure they fit in. If you're uneasy about the force that needs to be applied: I will send you replacement parts if you break them!
 

the paint came from the hobby store from their model paint rack, I used Burnt Sienna and While (glossy). 

Thanks for the paint specification - the other simple-but-very-good paint tip was one I heard at VCF MW last weekend: Nutmeg Brown from Walmart. It's fractionally darker than the original colour, but that makes it look even better (IMHO) than the custom paint I had mixed up for my last batch of PiDPs.
 

On the switches I found that I needed to trim the skewer down to about 2mm extending on each end

Correct. The Skewers need to be clipped. That's already in the Building Instructions though.
 

, I may end up building a short cable and put a small IDC cable between the front panel and the Pi. Also it might make sense to start with a Beaglebone Black as it has more I/O's and would not need the serial hack, but other than that I think the choice of the Pi is fine.

I'd be very interested in feedback on the Beaglebone. It is the board I am ogling for an upcoming PDP-11...

If you respin it, I would consider making it about 3mm larger all around. The PC board could accomodate the full switches at that point

I thought about it, but it adds a good few dollars to the kit because of the price threshold if I go outside the 10*30cm limit.
 

I would also consder making the front panel connect to the PI with an IDC cable, That would give you more flexibility with routing cables in the box.

The problem (if I am not mistaken) is that this becomes an either/or choice for the PCB design. Either you have a connector for a Pi mounted onto the back, or you have a ribbon cable connector. Because a ribbon cable needs the rows in mirrored order compared to a direct mount. As most people will prefer direct mount, I think the compromise solution is the direct-mount option, and when you want to use a cable mount, you have to use two single-row ribbon connectors to avoid the mirror-image problem.

All in all its a great piece of work, and I've enjoyed it tremendously. And I'm glad my friend Mark spotted it :-).

Thanks for the good feedback! But I feel we need to fix your problem of fitting the plexi in the case. I suspect it's just that you are too gentle in 'bending/forcing' the plexi into the case. After all, the box came with the plexi fitted into it!

Regards,

Oscar.

[Vince Mulhollon]

On Wednesday, September 2, 2015 at 10:04:40 AM UTC-5, Obsolescence wrote:

After all, the box came with the plexi fitted into it!

Almost... I need to verify this when I get home, but I was under the impression my front panel was extremely tight one time until I flipped the box upside down, I had rotated the box 180 degrees, top of the panel to the bottom of the case etc.  It fit perfectly one way, tight when flipped.

There really is no such thing as a rectangle in a manufactured part... a machinist with expensive enough tools will measure all rectangles as trapezoids, all of them, and a thousandth might be the difference between a tight fit and too tight fit.

Of course if you drill cable holes on the wrong side, you might not want to flip it to fix it.

Anyway its worth a try.

[Bill Laing]

In an effort to improve the opportunity to fit the board I'm going to trim off the lower switch mounts about half way through the mounting hole. As they are they stick out past the plex on the south end further hampering mounting it in the box.

I have cut and scraped the material behind the lower switch mounts so that the front panel fits properly into the box at the bottom. I also scraped the bamboo away on the top right of the case as the front panel was proud of the case in that position. It does take a little patience but I am satified with the fit of the front panel now.

[Jeremy Radwan]

My front panel wasn't one of the "snug fit" ones and the bottom potion stuck out a bit beyond the wood case because for some reason my switches wouldn't sit flat on the PCB. At any rate, I decided to go with velcro to attach the faceplate so it's easily removed (I didn't have any magnets lying around that would work for that option). This means the faceplate sticks out from the wood case, but at least it's even and doesn't look too bad. This also gives me some edge purchase to make it easier to remove the faceplate (since the velcro is pretty sticky).

I've also chosen, at this point, not to attach the wood blocks to the back of the case. Again, I'm thinking about removability and I didn't want to risk cutting the large slot in the side of the wood case to access ethernet and USB. With the faceplate velcro'ed in place, the PCB is pretty well held in place so this way I can remove the faceplate and then remove the PCB if I need to get to HDMI/ethernet/USB for some reason.