DIGI-COMP I - Introduction

Parent Category: Articles Category: DIGI-COMP I Written by Administrator

DIGI-COMP I ("one")  is a mechanical calculation device, delivered in kit form. It consists of 3 flip flops and programmable logic. Originally manufactured from polystyrene parts by E.S.R. Inc starting in 1963, it is as old as I am!
It was sold as an educational toy for just $4.99. Sales passed 100.000 and stopped in the 1970s with rise of electronic toys.
See https://en.wikipedia.org/wiki/Digi-Comp_I and E.S.R.

digicomp1 alone total small


Here it is running here (driven by a self-built motor), programmed to implement a binary counter:


This "binary counter" application as well as detailed functions are found in the user's manual, see attachement.

And: DIGI-COMP I is not to be confused with DIGI-COMP II ... that one is a nice looking marble calculator, but not programmable.

A mechanical state machine

For modern eyes DIGI-COMP looks quite confusing (as most mechanical calculation devices). So what exactly is it?

Original marketing praised DIGI-COMP as "The first real operating digital computer in plastic".
Well, yes. More realistic, it is a 3 bit finite state machine. But sure, made from plastic.

Core element are 3 clocked mechanical flip flops, implemented as 3 horicontal sliders which can sit in "0" or in "1" position.

Flip flop "outputs" can be combined via some mechanical AND and OR conditions, the resulting values are used to "set" or "clear" flip flop sliders in the next clock cycle. So one set of flip flop states generates the next one via a combinatorical function. The Wikipedia article on Moore machines has a nice diagram of such a machine. DIGI-COMP's flavor is the simpler "Medvedev machine":

Medwedew Automat digicomp

The combinatory logic function which calculates the next 3-bit state from the current one is "programmed" by settings various white "tubes" onto "pegs" in the mechanical logic. This makes DIGI-COMP very versatile.

As the original package claims: "See how a computer adds, subtracts, shifts, complements, multiplies, memorizes, compares, play challenging games, solve problems, process data, answer riddles, do the missile count down, satellite re-entry, missile checkout and many other problems". And yes, the manual has many programming examples to implement all this.

Programming? with tubes and pegs?

To understand DIGI-COMP, we better separate the Architecture from its Implementation:
Architecture is a timeless Medvedev state machine, consisting of storage flip flops and a combinatoric logic feedback.
And it is implemented with 1960s toy technology: manual clock, plastic sliders, wire rods and tubes and pegs.

digicomp1 tube on peg

Despite it surely does not look so, programming DIGI-COMPs logic with these white tubes is also quite current technology (more or less).

DIGI-COMP has a pre-construced logic pattern (slider and rods) with variable elements (tubes on pegs). These tubes enable or disable certain mechanical AND and OR terms. Their state for a given application is to be documented in a "coding sheet", here shown for the "binary counter".

coding sheet original

Modern Programmable Logic Devices work the same way: you have a generic logic structure etched into silicon, the actual function is giving at programming time by setting or burning some "fuses" in the silicon. So: "pegs"= "fuses".

FPGA chips work similar: they also consist of standard blocks of logic and flip flops, often called "logic cell" or "macrocell". A FPGA may have millons of macrocells, each a few 10s nanometers in size. For technical reasons the logic array is not implemented by logic gates and "fuses", but as a small RAM area holding a thruth table, called "Lookup table" (LUT). Wikipedias example adds an optional ALU element here:

FPGA cell example

So think of DIGI-COMP as a "3-bit macrocell", with the "tubes" as visible LUT content.


In contrast to modern nano-meter-sized and GHz-clocked silicon, DIGI-COMPs operation is visible to the naked eye.
So it makes a great tool for teaching logic design!

The Original Package

In Xmas 1963, you'd find DIGI-COMP I under your Xmas tree in this package (picture stolen from a recent eBay offer):

digicomp1 box

It came as a DIY set, as a bunch of plastic parts.

digi comp 1 parts 1

You had to assemble all these before use, anticipating our IKEA experiences.

The user manual itself is a retro-futuristic gem and contributes greatly to DIGI-COMPs success.

digi comp 1 instruction 1



Apparently there's a fan group for DIGI-COMP and similar devices at Yahoo: "FriendsOfDigicomp". I wasn't able to find their message digest, but their file archive is here:

Some interesting documents are attached below.

Modern Implementions

DIGI-COMP is still fascinating people, there are several projects around it. I found these links to be active in 2020:

3D prints

DIGI-COMP I can easily reproduced on 3D printers, because all parts are plastic and flat. For example see this project:


Very important: Thanks to these guys, it's easy to replace a broken 1963 part with own prints. Long life DIGI-COMP!


This is another project for 3D printer, but a modified design:


Minds-On Toys Digi-Comp v2.0

This one is commercial. DIGI-COMP is made from card board instead of plastic.


Check out their site, lots of good info.

Online simulator

This is a web based simulator.


You can develop own logic programs, and save and reload them later.


Of course! http://www.nico71.fr/lego-computer-digicomp/


Download this file (coding-sheet.pdf)coding-sheet.pdf[DIGI-COMP I Coding Sheet as PDF Form]50 kB
Download this file (DC1 Detailed Programming.PDF)DC1 Detailed Programming.PDF[DIGI-COMP I Detailed Programming]3393 kB
Download this file (DC1-PLA.pdf)DC1-PLA.pdf[DIGI-COMP I as PLA (by friendsofdigicomp)]47 kB
Download this file (digi-comp-1-instruction.pdf)digi-comp-1-instruction.pdf[DIGI-COMP I User Manual]13713 kB
Download this file (digi-comp-1-parts.pdf)digi-comp-1-parts.pdf[DIGI-COMP I Part List]1544 kB
Download this file (digicomp-romps.pdf)digicomp-romps.pdf[DIGI-COMP I Game And Problem Book]3561 kB
Download this file (Duerig.PDF)Duerig.PDF[DIGI-COMP I Personal Narrative about Invention and Marketing (friendsofdigicomp)]817 kB
Download this file (Patent_03273794.pdf)Patent_03273794.pdf[DIGI-COMP I Patent Original (friendsofdigicomp)]1122 kB