Every hackerspace needs a laser cutter. Unfortunately, they can be very expensive. Deals like the one Hacklab.to got don’t happen very often. However, there are factories in China turning out laser engravers and selling them on eBay for relatively cheap. We found a local distributor that appears to buy them directly from China, make sure they work, and resell them.

We received our laser in good shape. It came with a 240V blower (now junked), a 240V pump (also junked) and a 120->240 stepup transformer (now unnecessary) to power both of them. It also came with MoshiDraw 6 and a USB copy protection dongle.

It didn’t take us long to decide that MoshiDraw wasn’t going to work for us – the software and manual are badly translated and it doesn’t support vector motion (essential for cutting). The interface between MoshiDraw and the controller may be some subset of HPGL, but not in any useful way. Feeding HPGL directly from a file to the laser resulted either in nothing happening or in unpredictable, inconsistent behaviour, even when the file was produced by MoshiDraw itself.

At this point we decided to follow the route Hacklab.to took, and replace the internal driver electronics with a board that can read step and direction signals from LinuxCNC

Once that decision was made, there were two options: build a controller, or buy one off the shelf. There are dozens of commercially available stepper driver boards. They can be expensive, and most of them have more features than we need. Also, just buying a drop-in solution is no fun, so we decided to build one.

The driver is basically just a double implementation of the reference design for the Allegro A3982 plus an optocoupler to activate the laser and a connector for the end stops.

I chose the A3982 because it has a translator built-in (translates step/direction signals into the right sequence for driving a stepper), and because it’s available in SOIC which meant I could use an SOIC to DIP adapter when breadboarding the circuit and when building it on perf-board. If I were to get a PCB made, I would probably use one of the Allegro chips that supports 1/4, 1/8 or even 1/32 steps (only available in TSSOP or smaller). Be sure to read the A3982/83/84 FAQ if you decide to use the chip.

The only hard part of configuring LinuxCNC is the end-stop/home sensor settings – it takes a bit of thought and experimentation to get the right combination of approach direction, inversion of signals, identification of the signals, and so on.

We chose to use the Spindle ON signal to activate the laser because it’s the one that makes the most sense, and it should allow for PWM output when we decide to work out computer control of laser power. We initially routed that signal to parallel port pin 1, but discovered that pin to be active low – meaning that it is held high until LinuxCNC starts and takes control of the parallel port, possibly resulting in the laser being activated unintentionally.

Here are the important parameters for our laser:
Motor steps/rev: 400
X Leadscrew Pitch: 0.626 rev/in (determined empirically)
Y Leadscrew Pitch: 0.626 rev/in

Home X and Home Y signals in LinuxCNC are connected to the optical end stops on the gantry. Both signals are set to invert, and the Home Latch Direction is set to “same”.

The end result is that we have a laser that can easily cut 5mm acryclic, 1/4″ hardboard, 1/4″ poplar, and etch nicely on many materials.

The idea is this: buy a Power Wheels car, mod it to make it MOAR AWSOME, and race it against teams from other hackerspaces. Very simple.

We got ourselves a used Extreme Dune Buggy, and let Jason go at it with the Sawzall.

There was much drilling, lathing, cutting, grinding, and welding.

The organising people announced the Early Bird Challenge a few weeks ago – post a video of your car driving 150 feet, powered by the motor you intend to race with. We didn’t quite get the points, but we did post a video:

I have no idea who made it or where it came from. The interweb mentions it a few times, but there doesn’t seem to be any information about it.

A moment of inspiration hit, and I decided it would be neat/fun/educational to build it into a sort of glorious MIDI-controlled monophonic electronic tinny-sounding synthesizer.

Opening the case revealed that each button simply connects a pin on the controller chip (under the black blob) to the positive side of the batteries – there isn’t even a matrix, unlike most music and computer keyboards.

I soldered 30AWG wire-wrap wire to each trace, labeling them with the solfège names printed on the keys so that I could connect them in the correct order. Then I connected the wires to a microcontroller and programmed it to play a simple tune.

With the proof of concept done, I moved on to the next step.

It turns out that reading MIDI using a microcontroller is very easy. I used the circuit and code (with a little modification) from here to read MIDI signals from my keyboard and turn on LEDs.

The final step was to combine the two circuits into one MIDI-controlled, Arduino-powered, piezo-speaker-somethinged monophonic synthesizer:

The fun in this project was in building it and seeing it work, rather than in having it once it’s done. I would be just disassembling it to reuse the parts, but in this case my cousin (who makes electronic music) is interested in it, so I’m going to rebuild it on perfboard in a proper case, with a jack for audio output, and maybe some interesting stuff to use up the remaining four pins on the microcontroller. More on that later.