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.

Cool new 3D printers

I don't want to fall into the habit of only blogging once per year about MakerFaire. So this post is actually about a crop of cool new 3D printers, and I'll probably see a few of them there, but it's not about MakerFaire proper. These all fall in the $1500 to $2500 price range.

First up is Makerbot's Replicator 2. There is some controversy around this one, because it's a mix of open source technology under the GPL, and some new technology that's very likely not open source, which allows for a much higher print quality. The open source 3D printer advocates are concerned that it violates the GNU General Public License. The open source technology is primarily the work of Adrian Bowyer who started the RepRap project, and he's given (unenthusiastic) permission to Makerbot to use it.

One of the RepRap enthusiasts is my friend Jeff, who will have a table at MakerFaire this year to show off the printer that has occupied two or three years of his nights and weekends. I like Jeff and I think he'll probably not be too happy with Makerbot's decision to include closed-source technology. But the step up in quality for the price is pretty appealing for a non-GPL-purist like myself. I don't worry about running GPL software on closed-source laptops, after all.

Second is the FORM1 from some Media Lab folks. I don't know much about these folks or their history, but the Media Lab has been at the cutting edge of high-end 3D printing for a couple of decades now, so they've probably got something pretty interesting. I think their raw material is a liquid rather than the long plastic spaghetti sticks used by most other affordable machines (based on one photo on their Kickstarter page). This is the most expensive of the lot, price currently listing as $2500.

Third is the UP!Plus from 3D Printing Systems. Their output doesn't look as nice as the Replicator 2 or the FORM1, but they are at the more affordable end.

What's cool about all these printers and some other new ones is that the user friendliness and quality of output are improving rapidly in recent years. Before long, these things will be popping up in homes, dorm rooms, high schools, and the local mall.

Makerfaire NYC 2012 is this weekend, and I'll be there to checkout 3D printers, microcontroller boards, art installations, and whatever else is around, and I'll blog about what I see.

Adrian Bowyer interview, Computerworld

Here is the start of the four-page interview. Much of this is stuff that's been published before. Two parts I found interesting appeared on the third page.

Are there plans to modify the current design to replace non-reproducible parts such as bolts with parts that can be manufactured on the machine itself, bringing the overall RepRap design closer to 100 per cent self-reproduction?

Yes - that is definitely one of the evolutionary paths to greater reproductive success. For the immediate future I will be concentrating on widening the list of materials that RepRap can build with (starting with electrical conductors). That widening will implicitly raise the proportion of parts that it can make for itself, of course.

The Fab@Home people have already done a few embedded circuits by printing with conductive silicone. Making circuitry will be a very important ability for these machines.

Can the RepRap recycle what it manufactures?

Yes, recycling has been built in from the start... The main plastic we are using is polylactic acid...

But I want to move to using a non-biodegradable resin. This too is sourced from biomass, but is stable in the ground. That means that the more reprapped goods that get made from it and thrown in landfill, the more carbon is taken out of the atmosphere and locked away for good. And, in 200 years when we have taken so much carbon out of the air to make stuff that anthropogenic global cooling is starting to be a problem, the landfill sites become our strip coal mines to save us.

This is the first time I've ever heard anybody advocate for putting stuff INTO landfills as an environmental measure. An interesting approach to carbon sequestration.