By popular demand, I’ve added a new feature to the Apple II firmware for the Floppy Emu disk emulator: auto-mounting of the previous floppy disk image. If you turn off the computer while a disk image is inserted in the emulated floppy drive, the next time you turn the computer on, Floppy Emu will skip the menus and immediately load that same floppy disk image. This is a nice time saver if you tend to use the same disk image every time, but it’s buried in a sub-sub-directory on your SD card. It also makes it possible for an Apple IIc, IIc+, or IIgs to cold boot directly from a floppy disk image. Previously it was necessary to select the desired disk image from the Floppy Emu menu, then soft-reset the computer by pressing control-apple-reset.

apple-II-0.1P-F8 – Apple II, for Model B
apple-II-0.1P-F6 – Apple II, for Model A

I welcome your feedback on this change. While the convenience is undeniable, I’m not completely sure I like the new behavior. After the power is turned on, if the Floppy Emu is going to auto-mount a disk image, there’s a very short window of time during which it can be done. In order to auto-mount the floppy image quickly enough for the computer to boot from it, the Floppy Emu must skip the normal self test (smiley face logo) and version info screen (diagnostic info, and emulation mode selection). This may be a little confusing for people who are looking to verify their current firmware settings, or change the emulation mode. They can eject the auto-mounted disk to restore the normal startup screen flow. What do you think?

It’s high time for a new project here at BMOW. These days I spend so much time on Floppy Emu, it’s hard to squeeze in anything else! A new project would help stir things up, and get the creative juices flowing. Here are some ideas I’ve been kicking around:

Electric Scribbling Machine – I described this one in yesterday’s post. It’s a tripod with colored pens for legs, and a motor that makes it move, drawing tracks on the paper beneath it as it goes. Yesterday’s post described a “vibrabot” design using an offset weight on the motor shaft, which randomly jiggles the machine and creates interesting erratic drawings. I’ve since been working on an alternate design in which the motor is used directly as one of the legs, which spins the whole machine in rapid circles, and creates elegant looping drawings somewhat reminiscent of a Spirograph.

USB Keyboard/Mouse Adapter for Vintage Macintosh – Classic Macintosh computers like the Mac SE and Mac II series used input devices based on ADB – the Apple Desktop Bus. The Mac Plus and Mac 128K/512K were more primitive, and used custom protocols for keyboard and mouse rather than any bus-based system. Both systems are fairly well documented, and I have some experience with them already. Using a modern microcontroller, it shouldn’t be too difficult to build an adapter that functions as a USB host for a modern keyboard and mouse, and translates the input data to ADB or the Mac Plus protocol.

Weather Logging Station – A few years ago I designed the Backwoods Logger, an ultra-tiny portable weather station. I envisioned it mainly as a graphing altimeter for people going on mountain hikes. After many discussions with interested people, it became clear that most people didn’t care about portability, or about having graphing functions or even a screen. What they wanted was a stationary module that could take regular temperature, pressure, and maybe humidity readings, and save a history of weeks or months of data. There are already a few designs like this, but maybe they’re too intimidating or their feature set isn’t quite right, because I still get occasional emails from people asking for something like this.

Nibbler Kit – Nibbler is a 4-bit CPU that I designed entirely using basic 7400-series logic elements. It was a one-off project for my own entertainment. William Buchholz later designed a nice Nibbler PCB for his hacker group, which got me thinking that something more polished would be nice. My web stats say the Nibbler pages are some of the most popular content on this site, so maybe there would be enough interest to justify a Nibbler kit? My only fear in offering a kit for something this complex is the potential support headaches. It might make more sense to offer finished Nibblers instead of kits, though that would take some of the fun out of it.

Electric Bow Tie 2.0 – As with the Backwoods Logger, I think I misjudged popular interest when I designed the Electric Bow Tie Kit. It’s fun to have neckwear that blinks and beeps, but mostly people don’t seem interested in assembling a kit – they just want something kitschy they can wear to a special event and get some laughs. I can say from personal experience that the blinking effect is fun, but the beeping effect starts to grate on your sanity after about 60 seconds. Electric Bow Tie 2.0 would probably drop the sound effects, but add many more LEDs controlled by a microcontroller, enabling all kinds of entertaining and annoying patterns like chase lights and starbursts. I’d also try to replace the 9V battery with one or two smaller CR2032 batteries to reduce weight.

I’m working on a design for a “scribbling machine”, similar to the concept shown here from Make Magazine. For the past three years, I’ve led groups of children through a scribbling machine construction project at our school’s annual Discovery Day event. Take a motor with an offset weight on its shaft, attach it to some kind of tripod with colored pens for legs, and add 25 third graders. The offset weight makes the machine vibrate unpredictably, drawing patterns on the paper beneath it as it moves. Every time I’ve done this project, it’s been lots of fun.

Kids, motors, and pens – what could go wrong? Quite a lot, as it turns out. The first year, we used plastic drinking cups as the platform. These were a little too flimsy, and the tapered shape of the cup often caused the offset weight (a piece of glue stick) to whack the cup’s side with each revolution of the motor. For the second year, we used recycled plastic water bottles, with the motor mounted vertically in the neck of the bottle. This solved the clearance problem, but the motors sometimes fell inside the bottles, and the whole platform wasn’t well-balanced to create pleasing scribbles.

Attaching pens, motor, and battery to the platform is more challenging than it seems. The Make design in the photo shows everything held by tape, but we found this didn’t provide a secure enough mount, especially for the motor. We used rubber bands, which had the added advantage of being removable and reusable, to encourage experimentation. But the tension of the rubber bands sometimes deformed or crushed the cups and water bottles. We also learned that many children this age lack the physical dexterity needed to use rubber bands this way. They’d get a few rubber bands on, but then mess up the first ones as they tried to add more, or even get their fingers stuck.

The biggest challenge for the kids has consistently been making a reliable electrical connection between the motor and battery. We tried taping the wires to the end of a battery or using rubber bands to hold the wires, and it works if you’re careful and patient, but those adjectives don’t describe most third graders. Even when it works, this method doesn’t provide any way to turn the scribbling machine on and off, except by disconnecting the wire again. We saw many frustrated kids that couldn’t get their wires to stay put, or whose machines would repeatedly stop running when a wire wiggled loose.

 
Electric Scribbling Machine 2.0

For this year, I decided to create a completely new platform to address all these issues. It will use a real 2xAA battery holder with built-in on/off switch. No more flaky connections! Kids can twist the wire leads onto the motor terminals, and use tape or hot glue to hold them in place. To solve the stability and fragility problems, I’ve designed a laser-cut platform to hold the pens, batteries, and motor firmly in place. The battery holder goes in the center, the motor is mounted lying on its side with the shaft extending beyond the platform’s edge, and three pens are inserted into any of the many pre-cut holes. By changing which holes are used as pen mounts, and moving the battery and motor, the kids can experiment with differently-balanced machines to see how their behaviors differ.

If the platform is cut from wood or another soft material, I can also include various offset weights with tiny pre-cut holes that press on to the motor shaft. These would replace the glue stick offset weight, and enable easy experimentation with different lengths and shapes of weights, including weights cut into strange shapes.

To attach the parts to the board, I plan to use rubber bands again, but in a simpler way than before. Surrounding each hole in the platform are two U-shaped cut-outs, which create two pegs on opposite sides of the hole. A rubber band stretched between these pegs will hold a motor, battery, or anything else mounted flat against the board. To mount pens vertically, two rubber bands can be used, one each around the pen shaft and a single peg. Or the job can be done with one rubber band that’s twisted twice when it passes around the pen shaft. With the right tension, this should hold the pens vertically and prevent them from slipping out.

 
Scribbling Economics

This all sounds good, but what will it cost? Discovery Day projects have a budget of $50, which works out to about $2 per child. They’re supposed to be quick and easy projects, with no soldering or other skills needed, that can be completed in about 45 minutes including time for experimentation and play. In past years I’ve spent closer to $3.50 per child, and paid the extra out of my own pocket. For this new design, the battery holder with switch adds another $1.00, and because 1xAA holders with a switch don’t seem to exist, I’ve gone to 2 AA batteries and an additional $0.30 expense.

That’s not too bad, but the potential deal-breaker is the laser-cut platform. Even after optimizing the platform design to make it as cheap as possible, it’s still going to cost between $3 and $7 each to make these platforms, depending on the material used. Even if I aggressively seek the cheapest sources for motors, batteries, and pens, and use the cheapest possible platform material (cardboard), I’m looking at a minimum cost of $5.68 per child, or almost 300% of the budget. In absolute terms that’s not a big deal – it’s only about 25 kids, so it would require an extra $75 or $100 from me out of pocket to make a cool project for the school. My real concern is what that would mean to the other projects. In other words, will I cause problems or bad feelings if I provide a $5 or $10 project when the other leaders provide a $2 one?

I’d assumed plywood would be the cheapest and best material for a project like this, for making both the platform and the offset weights. A small hole cut in a 3 mm sheet of plywood should press-fit onto the motor shaft, which testing will confirm. Unfortunately plywood turned out to be the most expensive option of the ones I considered – $6.74 per platform. The material itself isn’t expensive, but the estimated laser cutting time is higher than the alternatives, and that dominates the total cost. Clear acrylic would be cheaper at $5.24 per platform, but because acrylic doesn’t have any give to it, it can’t be used to make press-fit offset weights. Maybe I could cut the platforms from acrylic and the weights separately from plywood.

The cheapest option is cardboard. Cardboard, you say? Would that really be strong enough? I’m not sure, but I think it might be. Two-ply 6.7mm cardboard and one-ply 1.5mm cardboard would both be about $3.00 per platform. I have some one-ply 1.5mm sample material, and it’s surprisingly rigid. There’s also a one-ply 4.0mm material available for the same price, but my guess is that won’t work as well for the rubber band mounting pegs.

I also considered making the platform as a printed circuit board, from a PCB service like Seeed. The circuit board probably wouldn’t do anything – it would just be a substrate. The cost for a 150mm diameter circular board would be about $5 each, similar to the laser cut acrylic. But I don’t think PCB material could be used to make press-fit offset weights, and PCB manufacturers don’t usually like to cut internal slots like those U-shaped peg cut-outs.

I’ll get a few sample cardboard platforms made, the next time I place an order for other laser-cut parts. If cardboard is strong enough, that’s probably the least expensive solution. The only lower cost alternative would be scrapping the laser-cut platform idea, and using a 2xAA switched battery holder on some random recycled material as the platform. But that wouldn’t be as cool. 🙂