Silicon-free computer on vacuum and cold-cathode tubes with pure brainfuck instruction set

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Decatrons can do +1 and -1 operations by desing, so they are best devices for brainfuck instruction set.

As a next generation of BrainfuckPC, DekatronPC should have next characteristics:
> 8 instructions - pure brainfuck only without RLE;
> 10k or 100k IP counter;
> 256 data counter;
> Harvard architecture;
> Up to 40kHz clock(as A103 can do that) - 10kHz clock is acceptable;
> ROM and RAM size - currently unknown;
> RAM device - ferrite core memory


DekatronPC is next project after BrainfuckPC relay computer. 

I made some architectural mistakes in relay computer and want to create more clear an much more insane device.


Harvard architecture with separate memory for code and data

30000 8-bit cells.

Decimal data representation

Instruction Set

Main point - pure brainfuck. If BrainfuckPC have fully-functional 16-bit adder and can ADD/SUB any 8-bit of 16-bit CONST, DekatronPC due to dekatron feature can do only +1 and -1.

DekatronPC instructionbrainfuck equivalent description
INC+Old value from current memory cell is loaded into dekatron counter, incremented and stored back
DEC-Old value from current memory cell is loaded into dekatron counter, decremented and stored back
ADA>Increment number of current memory cell (go forward through memory)
ADS<Decrement number of current memory cell (go backward through memory)
IN,Read ASCII symbol from terminal and store it in a current memory cell
OUT.Write value from current memory cell to a terminal
[[If value of current memory cell is not zero - do nothing.
If zero - increment IP pointer while the end of this loop is not founded
]]if value of current memory cell is zero - do nothing
If not zero - decrement IP pointer while the begining of this loop is not founded.
NOPn/aUsed for loop alignment


DekatronPC can be used in two modes:

  •  In clear lamp mode. Ferrite memory work in direct mode  - when program is loaded directly to instruction memory and data memory working without any external storage. No transistors are used in this mode, but we are limited with 3KB of instructions and 1.5Kb of data.
  • In insane mode. Ferrite memory works in cache mode and external storages are used for storing instructions and data. No size limitations, but outside lamp logic we can use transistors.

Hardware, which can support described instruction set can be implemented on four reversible dekatron counters:

  1.  IP counter - can count from 0 to 999999 (6 dekatrons). Just represent current instruction number
  2. Loop level counter - can count from 0 to 999 (3 dekatrons). Used for cycles limits lookup
  3. AP counter - can count from 0 to 29999 (30000 memory cells ) (5 dekatrons). Just represent current memory cell
  4. Data counter - can count from 0 to 255 (3 dekatrons). Used for loading data from memory, modifying it, printing, reading and storing in memory

Just only 17 dekatrons are needed to make the whole device. But each dekatron require up to 10 vacuum tubes. 


valves and tubes datasheet

Adobe Portable Document Format - 10.48 MB - 02/02/2018 at 09:24


Adobe Portable Document Format - 1.08 MB - 02/02/2018 at 09:23


Adobe Portable Document Format - 748.14 kB - 02/02/2018 at 09:23


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Ken Yap wrote 06/16/2019 at 11:47 point

Cool! Dekatrons, I remember those. Counter and display in the same tube. What's not to like? 👍

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Dave's Dev Lab wrote 04/16/2018 at 22:14 point

Hey Artem! the witch document you have is a very old version, i have an updated one with new graphics and corrections -

also, all of the WITCH documentation i have can be found in my github including recreated drawings:

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Artem Kashkanov wrote 04/21/2018 at 07:39 point

Wow! Thanks for clearing the document!

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roelh wrote 02/03/2018 at 18:34 point

Hi Artem,

sounds like a nice project !

In your title you talk about 'other cold cathode tubes' , so I think you will like the clock with neon tube counters made by a Dutch guy:

I don't know how may decatrons you have, but instead of a brainf*ck computer you could perhaps build a more 'real' computer like the witch (that you will know):

But you could build a version with real decatrons instead of chip counters. You could be the first one to build a computer or calculator without transistors or chips (tubes only).

The witch uses decatrons (quite a lot) for the main memory. If you plan to use ferrite memory,  you will need the decatrons and other tubes just for control functions, and then the 30 that I see on your picture might be enough.

The 'real' computer, as I see it, will only have move, increment and decrement functions. But you will need several pointers to memory, and a displacement in the instruction, to create a indirect-with-displacement addressing mode that will lead to an efficient processor. Increment and decrement can be done by your decatrons. In another implementation, increment and decrement would only need a shift and an XOR gate, to count in a LFSR sequence. 

Your 'real' computer could demonstrate arithmetic and trig/log calculations, as well as playing Tetris or other fun stuff.

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Artem Kashkanov wrote 02/03/2018 at 20:37 point

Thanks for your advices! 

I know about Dutch guy clock - I thought to build the same one using MTX-90 tiratrons, but why to create yet another clock... 

Currently I have 25 dekatrons - USSR models: A101, A102, A103 It might be enough to build architerture like BfPC - with three bi-directional counters - IP counter, AP counter and Data value counter.  

Anyway I have no idea how this project will look like, just assume the same arch as my current project, but you noticed right thing - this would be silicon-less device.

Mandatory requirement - tubes only (with some few relays).  

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