Thursday, May 26, 2011

UptownMaker goes to the Faire

This past weekend I attended Maker Faire in San Mateo. It was an absolute gas (does anybody use that phrase anymore?)! I'm going to do a few quick posts highlighting my favorite sights- all my pictures and videos are on my Picasa site.

I'll start out with my favorite first: Miss Haley Who, swamp kirin wrangler.

This lovely fellow is a mechanical swamp kirin. He stands about nine feet tall and though he looks ferocious he's really quite gentle.


Haley Who, aka halo seabat, built this majestic creature as a gift for her little brother, Seth. It seems Seth was a bit heartbroken after their father explained that the few remaining wild swamp kirins in the east were best left unmolested in their natural habitats, and halo took pity on her brother, building him this mechanical version.

The pair of them wandered about the grounds, charming the pants off of just about everybody they met. Haley's disarming smile, the kirin's gentle gait and their tender interplay softened the overall image to the point where I never saw even the smallest of children exhibit any fear at all- mostly they wanted to touch the kirin, stroke its legs, even kiss it on the nose.

It felt magical, and I'm a happier person for knowing Haley and her kirin friend are out in the world.

Tuesday, May 24, 2011

USB CDC toy


This was originally going to be my calling card for Maker Faire. It's a very simple implementation of Osamu Tamura's AVR-CDC project, realized without a board. I had planned to make it a small device that can be plugged into a USB port and observed on a terminal spitting out information about me. The Great Global Hackerspace Challenge project took a lot out of me, though, so I didn't get it done in time.

The blobby on the left is an I/O module- three input switches, three output LEDs, and a reset switch and power LED. It plugs onto the header that is currently being used for programming. The circuitry is pretty simple: 100nF bypass capacitor, the 5V in from the USB port goes to the positive supply pin through a 1N4001, and the USB D+/D- are connected to a couple of the I/O pins.

Some words about that 1N4001: it was chosen specifically for its high forward voltage. See, the USB input wants a 3.6V input or so, and the AVR doesn't want to run at the 16+MHz needed for this project below about 4V. Originally, following the schematic on the project home page, I was using a red LED as a voltage drop. The AVR never ran stably- the voltage (about 3.3V) was just too low. Now, it's running at about 4.2V, and the 68-ohm resistors between the AVR and the USB limit the current to just a few mA, and everybody's happy.

Right now, I'm up to my elbows in the source code of the original project, removing the serial I/O code and replacing it with easily used hooks for internal functions. Ultimately I'll bend it to be programmable through the Arduino interface- for now I'm working in AVRStudio5. Once I have it all done I'll release all the deets so anybody can make one. I may also make a PCB and sell kits for it through NoCube, and probably just the pre-programmed IC, as well.

Inductive power

About two years ago I decided I was going to figure out a cheesy inductive power coupling circuit. I sat down one Sunday, started plugging some stuff together and this is what I ended up with:

This is the circuit I brought with me to the "bring-a-hack" dinner at Harry's Hofbrau that Jeri Ellsworth organized on Sunday night. You can see that the LED in the jar is lit- the jar is really just a gimmick and the little parasite works better outside the jar.

The circuit is very simple: the IC in the middle is a 12F683 that I programmed up to be a square wave generator (someday I'll blog that project, but for now, I'll just say that the oscillator frequency is jumper selectable and it can be set to either update constantly when powered or set and forget the output frequency and duty cycle) running at 50% duty cycle and (approximately) 71kHz. The square on the right is a bit of ~28ga magnet wire wrapped a few times around four screws. Power is delivered to it by a transistor- the coil gets driven by the full umph of the 9V while the PIC runs on the 5V regulator to the left.

Efficiency is TERRIBLE. Because I'm driving the transistor hard with a square wave I lose energy into the higher-order harmonics, and then I'm half-wave rectifying the output with the LED. If I made the drive waveform more sine-like and added some joule-thief circuitry to the parasite I'd see much better results. But then, this was never intended to be a huge project, just proof-of-concept.

One last thing, if you're thinking of doing this yourself: every hand-wound parasite is going to have a slightly different optimal frequency. The circuit as I made it was basically an LED, a 100nF capacitor and a coil all in parallel. Depending on the resonant frequency of the LC circuit, you'll see better results at different frequencies.