PDP-8/I replica- front panel questions

[Oscar]

Hi,

I'm designing a front panel for a PDP-8/I replica project. This will be a low-cost replica, but I'd still like to make it as faithful to the original as the budget allows.

Below is what I have so far: a PCB plus the acrylic front cover I designed for it.

My problem: I've never seen a PDP-8/I in real life. It proves very hard to establish the correct colors from the various photos I found off the web.
So, the question is, can anyone with access to a real 8/I perhaps help me judge the colors? Most practical is maybe if I can send a picture with a range of color variants to pick from.



Details: the idea is to plug a Raspberry Pi running a modified simh into this PCB. The Raspberry GPIO drives an array of multiplexed LEDs and switches. The picture shows the front panel artwork slightly translucent, so you see my PCB and a real PDP-8/I shining through it. The glowing lights are on the real PDP-8/I, the dimmed LEDs are on my PCB behind the front panel artwork.

I got the panel to be more or less pixel-perfect versus the originals. Except that I am committing sacrilege by rescaling the unit 2:3, and by chopping off the part of the real PDP-8/I outside of the red box - this keeps the cost of the acrylic front panel well below $40. The switches will not be the authentic ones either, but comfortable to work on.


So I guess my question is, would a fortunate 8/I owner help me judge the colors (the brown, yellow especially)?

Kind regards,

Oscar.

 

[jackrubin]

Oscar,

I'm sure you will find many photos on the web to give you a better idea of the true colors. They are much more orange and yellow rather than brown and yellow. The original panel ghosted behind your graphic doesn't look too bad. You can expect to find some variation across existing machines and probably none of them are exactly as they were when they were factory new. You will find even more variation across digital cameras and photographic images and yet another level of variation when you have deal with web rendering, web browsers and monitor color calibration.

If you want to do an accurate color match, you need to use something like Pantone reference colors against a bunch of existing machines and then make your best guess at some sort of representative color set. I don't have a Pantone panel but if you have sample patches, I'd be glad to compare them to my 8/I

Jack

 

[Al Kossow]

Hi,


My problem: I've never seen a PDP-8/I in real life. It proves very hard to establish the correct colors from the various photos I found off the web.
So, the question is, can anyone with access to a real 8/I perhaps help me judge the colors? Most practical is maybe if I can send a picture with a range of color variants to pick from.

The cabinet colors were specifed in DEC Standard 92

http://bitsavers.org/pdf/dec/standards/EL-00092-00-0_F_Finish_and_Color_Standard_Dec82.pdf

Not that I have any idea where to find a modern Pantone equivalent.

 

[m_thompson]

If you click on the 8/I image here: http://www.ricomputermuseum.org/Home/equipment/pdp-8-i
You will get a high-res image of an 8/I. It has an OEM front panel, but the switch colors are normal.

If you make the replica 8/I front panel narrower than the real one it will be too narrow to mount in a 19" equipment rack.

 

[Oscar]

All,

Thanks! With the colors updated as per below, does this look like a good color scheme to you? (pls ignore the switches)

Two last questions:
- is the front panel background pure black, or some sort of grey?
- the white lettering: pure white, or light grey or even ivory?




Jack,

Indeed, the colors I picked from the various 8/I pictures on the web are all over the place. To the point where orange and brown become confused. Never realised color was such a delicate topic - I spent a few hours googling...

Al,

Thanks! This document, I think, solved the problem. Section 5 defines the colours, albeit in old colour systems I had to figure out. so:
The dark brown is "Dark Luggage Tan", Munsell code 5 YR8/4, which is RGB 934f1f if this link can be believed.
The orange is CHM4 in the Color Harmony Model, which is close to RGB b66702 if this picture is reliable.
The things you learn on a Tuesday afternoon...

m_thompson,

I think that machine was the one I used as a template. Although based on a different picture actually. But note it has a nonstandard header - if that's the word.

If you make the replica 8/I front panel narrower than the real one it will be too narrow to mount in a 19" equipment rack.

Keep in mind I'm rescaling the machine to be 33% smaller than the original anyway. It is not intended to be a perfect clone, just striking enough to be, erm, evocative.

Regards,

Oscar.

 

[Oscar]

Hi,

My budget-PDP-8/I replica is getting near to completion. Using a Raspberry Pi and a modified simh, it runs pretty well now. Just a few indicator leds are left for which I am not sure when to make them light up correctly (Ion, Data Word).

I'm awaiting the acrylic front panel and an appropriate case, in time for demonstrating it at VCFeX in mid April. Here are some pictures of the machine sans case and sans acrylic panel:



Further details on my blog post on the project: http://obsolescenceguaranteed.blogspot.ch/2015/01/new-project-pdp-8i-replica.html

Regards,

Oscar.

 

[Lou - N2MIY]

Oscar,

Looks really sharp! I am looking forward to seeing it in person at VCFeX! You will have to let us know next time you do a run of boards. I am sure I'm not the only one here with a Pi that is looking for a good use for it. I will second the comment of one of the posters to your blog looking for emulated RK8E/RK05. Also add two KL8E serial ports (need one for the console terminal and another for the lineprinter).

How many euro each were the switches you used? The switches in total were probably the most expensive part of the project.

Lou

 

[m_thompson]

Just a few indicator leds are left for which I am not sure when to make them light up correctly (Ion, Data Word).

Oscar,

The ION instruction, 6001, enables interrupts and the IOF instruction, 6002, disables interrupts.
When interrupts are enabled the ION indicator is on.

Word Count will light when the processor does a Word Count cycle, a 3-cycle Data Break.
Current Address will light when the processor does a Current Address cycle, also part of a 3-cycle Data Break.

 

[Roe]

Oscar,

Looks really sharp! I am looking forward to seeing it in person at VCFeX! You will have to let us know next time you do a run of boards. I am sure I'm not the only one here with a Pi that is looking for a good use for it. I will second the comment of one of the posters to your blog looking for emulated RK8E/RK05. Also add two KL8E serial ports (need one for the console terminal and another for the lineprinter).

How many euro each were the switches you used? The switches in total were probably the most expensive part of the project.

Lou

There's a bit of a milestone for you, Lou; your 1024th post!

 

[Oscar]

Lou,

You will have to let us know next time you do a run of boards. I am sure I'm not the only one here with a Pi that is looking for a good use for it.

Thanks! I decided to not just publish the project as 'open source' design files and software, but also do a run of kits. Probably in early June.

I will second the comment of one of the posters to your blog looking for emulated RK8E/RK05. Also add two KL8E serial ports (need one for the console terminal and another for the lineprinter).

Actually, because this is just a front panel for SimH, you get all of its flexibility. So you can use ssh over wifi as a terminal, or use a dedicated HDMI screen/USB keyboard, or create access through however you want to reroute the emulated KL8E. The KL8JA additional terminals are also covered by SimH, as are RK05s, so it's just a matter of how you configure simh: disk images on the SD card, or on a plug-in USB stick. That was what swayed me towards the Pi with simh instead of a more custom solution.

The one thing I will do later on is to integrate the Pi's serial port into this, so there's not only the SimH/Linux I/O features but also the possibility to hook up a right proper vintage terminal straight away.

How many euro each were the switches you used? The switches in total were probably the most expensive part of the project.

Actually, they are not very expensive by themselves. It's shipping and import duties that make up their cost... the price totally depends on the volume I buy from the Chinese factory next time. But ball park figure: if I do a run of 100 PiDPs, cost is $1 per switch including Swiss Mr. Customs (charging ~40% for his kindly smile).

Regards,

Oscar.

 

[Oscar]

Hi,

The ION instruction, 6001, enables interrupts and the IOF instruction, 6002, disables interrupts.
When interrupts are enabled the ION indicator is on.

So light up the LED the moment you see 6001 as the current instruction, keep it lit until a 6002 comes along? Apologies, I have not delved into the PDP-8's interrupt logic at all yet.

Word Count will light when the processor does a Word Count cycle, a 3-cycle Data Break.
Current Address will light when the processor does a Current Address cycle, also part of a 3-cycle Data Break.

Thanks - I'll delve into the exact timing of LEDs this weekend! It's time to wrap it up now.

Regards,

Oscar.

 

[antiquekid3]

So light up the LED the moment you see 6001 as the current instruction, keep it lit until a 6002 comes along? Apologies, I have not delved into the PDP-8's interrupt logic at all yet.

Not quite. The global interrupt flip-flop is enabled by ION, but is disabled by IOF as well as when triggered by an interrupt.

I haven't delved into SimH's code base enough to know, but you should be able to find a single interrupt enable flag directly modified by ION/IOF.

Kyle