Monday, March 04, 2013

The Digi-Comp 1 rides again?

As computer people go, I'm rather an old fart, and my favorite childhood toy was this plastic computer, the Digi-Comp 1. See the three horizontal red things that run almost the full width? Those are flipflops, and the window on the left shows whether they are in the zero or one position. The six vertical metal bars in front are AND gates, and the little white tubes stuck onto the pegs on the fronts of the flipflops tell whether that bit is factored into the AND term. The six red plastic things on the top, together with similar stuff on the back, form three OR gates, which drive the values of the flipflops on the next clock edge. The two white sliders on the bottom worked in opposition, providing a hand-powered two-phase clock to drive all this stuff.

Over the past couple of days I placed an order with danger!awesome, a laser cutter shop in Cambridge MA. They have a nifty collection of laser cutters and were happy to hear that design files are available on the Thingiverse website. So I ordered some stuff and picked it up this evening, and that was fun. I had hoped they could make me this marble binary adder, but the designer didn't supply design files they could use. So no marble adding machine for me. Darn.
Thinking about that, my mind inevitably went back to the Digi-Comp 1. I started wondering whether I could build a Digi-Comp 1 using laser cut plywood, like the other trinkets I picked up this evening (a Companion Cube, a desktop trebuchet, a Shrimpbot, and a few little animals). Could that be feasible? The Digi-Comp 1 was basically a programmable logic array, which consists of two rectangular regions, one for AND gates and one for OR gates. On the Digi-Comp 1 these are respectively the front surface and the back surface of the device.

I thought about this for a while and came up with some very incomplete rough sketches to solve the problems of how the gates would work and how the binary values should be latched for one clock cycle. As with the Digi-Comp 1, this would be a rectangular thing with the AND plane on the front and the OR plane on the back. The flipflops would be horizontal bars along the front with two positions (left=0, right=1) and possibly the same window display that appears on the original Digi-Comp 1. The AND gates are vertical bars also on the front, connecting to vertical bars on the back. The OR bars on the back can move left and right if permitted. At a certain point in the clock cycle, the horizontal position of each OR bar is inverted with a little lever and latched as the new position for the corresponding flipflop. There is still a lot of mechanical engineering to think about. Should the bars be retracted with springs or rubber bands? There needs to be a lot of machinery to get everything to move when and where it's supposed to, and there needs to be a crank on the side to drive it. So there will be cams and gears and all sorts of fun stuff.

UPDATE: I found a place called Minds-On Toys that is selling a Digi-Comp kit which reproduces the exact mechanical design of the original. Looks very nice, except for the labor-intensive-looking bit at the bottom about fabricating your own plastic tubes.


Salvador said...

Sory. My English is very bad, but I'm very sure that you will can understand me.

Please visit this web

There you've got all the schemas that you need and all the pages of and old digi-comp 1's manual.
I think that is possible to make one in plastic (in red and white colors) with a 3D ABS plastic print.

Thank you for your article.

Salvador said...

This page is interesting too:

And theese one

Abby Digital said...

Hey, that's my picture up top there! Glad you had use for it, but I want you to know that it is NOT a photograph of a Digi Comp 1. Rather, it is a RENDERING of a computer model that I made of the Digi Comp 1, being nostalgic about the one I owned when I was a kid…

More renderings here: a few of which happen to also be other items I had as a kid, as well as an old computer or two. And animation too!