Don't go full Numitron ! Unless... OK whatever.

A project log for Hardware assembler / EMUI

Early computer designers were cheap masochists. This front panel is much better yet could have been made 50 years ago !

Yann Guidon / YGDESYann Guidon / YGDES 08/06/2019 at 03:292 Comments

The design of the front panel has evolved lately, as shown in the latest logs of #YGREC8: A new assembler panel. The interlocked switches have brought a new "touch" and "feeling" that beats the original design with only slide switches and rotary encoders.

This "new" increase in user-friendliness makes the disassembler panel's lamps (as planned earlier) look dumb and unwelcoming... What could I do ? Add more Numitrons, of course !

The immediate field is already taken care of with the #Numitron Hexadecimal display module so the rest should be easy, right ? Kinda sortof... But at least I have developed the techniques to make it easier, cheaper and smaller to build.

I made sure all the symbols could be represented in 7-segments displays: there are a few exceptions but the majority is unambiguous and explicit.

That's 10 tubes now...

There are several compromises but it looks much better than the originally planned panel with the many lamps.

I wonder if/how I could share the Immediate and SRI displays. Not to save a pair of Numitrons but to further reduce the clutter...

The opcodes look OK with 7 segments and 3 tubes :

XOR looks strange but I'll live with it.

The register names are easier:

There are a few obvious tricks to apply, as we'll see later.

Last but not least : the conditions

This one is a bit more tricky though because Z can't easily be represented and it would collide with 2. I also didn't want to represent Always as A, it should look inoccuous because it's used most of the time.

I adapted the design of the #Numitron Hexadecimal display module  and reduced the width to 3 bits / 8 codes. It was easy because the 0-1-2-3 codes were already working so I just added the 4 other codes :-)

There are only 5 relays (including a buffer and BTW I forgot to put a series resistor) but no less then 14+20=34 diodes. It's a single unit so I think the prototype will be OK (and I have already solved all the possible problems). Many diodes are doubled but I can't simplify it because it would break the balance of currents&voltages.

The register names are implemented twice. Each module uses 6 relays (+2 buffers) and 26+14 diodes. I have chosen a unipolar system to simplify things, yet it can be plugged to the existing Numitron tubes, in parallel with the hexadecimal decoder. There is a weird unbalanced binary tree...

The upper line (the letters) can be a classical array of diodes, and the output can join the anti-feedback diodes of the hexadecimal decoder. But I'm not sure it's relevant to save 2×7=14 diodes anyway... however there must be a way to disable the + and - supply pins of the decoders while the Numitron tubes share the 0V supply.

As expected, the opcodes are a bit more messy...

I chose a bipolar design to keep the number of relays low. There is also a fortunate coincidence : there are 3 buffer relays that each drive 3 relays (b11, b12, b13). There is a little crossover with the control lines of b13 and b12 to achieve that, which swaps SUB/OUT with CMPS/IN.

But that's it.

The equations for the segments will be another beast though... I don't know how many diodes will be necessary.



Dr. Cockroach wrote 08/07/2019 at 14:51 point

That is going to be awesome to work with and reading those display tubes will be a hoot :-)

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Yann Guidon / YGDES wrote 08/07/2019 at 14:57 point

I'm just wondering...
How reliable will this be ?
What part will break first ? The Numitrons ? the diodes ? the relays ?...

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