For PyroCardium to respond to people’s heartbeats, we need a way to electronically measure their heartbeat.   Since PyroCardium started life as a VU meter for music, the obvious way to do that was to hook up a stethoscope to a microphone.  Today I tried to do just that.

I had some cheap electret mikes leftover from an earlier project idea (a music responsive EL-wire cape that never made it off the drawing board), so I decided to do the obvious thing and jam one into the stethoscope tubing.  I then built a simple amplifier with a gain of about 100.

Hooking it up to the oscilloscope, I could see the trace move when I put the stethoscope on my chest, but I had no idea what it was responding to - if it was really my heartbeat, or if it was just noise.  It took me a while to come up with a way to figure out what was going on, but eventually I realized that I could hook it up to my stereo.  A few alligator clips later, I could hear my heartbeat booming out over my speakers.

I think our stethoscope amplifier is solved.

A couple of weeks ago, Erik did some great drawings of the hydrogen chamber in Rhino. Since then, we’ve been working to refine the design (uhh, we forgot a door… can we add one?) and build out the first level.  It was also cool to have Erik show us how he works in Rhino. The software combines the manipulation and viewing power of a 3d modeler like Maya with the accuracy and dimensioning capabilities of a CAD program. Perfect combination for this kind of work.

So far, first the six steel frames are welded, the aluminum for the surrounds is cut and drilled, and yesterday I got about half of the brackets welded on. It’s cool to see our physical work starting to look like the 3d model!

Those of you at our last few workdays will have heard me moaning about transients from our new solenoids causing the PyroCardium USB controller to trip off. The back story is that the 24V DC solenoids we had been using before turn out not to have seals compatible with propane. So I’d like to switch to some 110V AC solenoids I have which have propane compatible nitrile seals. I got 16 of these solenoids for free from my dad - they’d be about $800 new.

The problems began when I replaced the 24V solenoids with the 110V AC ones. As soon as I tried controlling them from the computer, the software crashed immediately. When you turn off a solenoid, the energy stored in the coil gives rise to a rapid increase in voltage across the inlets. This is called inductive kick. I have a varistor in place to dissipate this kick, but it doesn’t appear to be enough - my theory is that this transient voltage spike is getting coupled into the USB board and giving rise to errors. This theory is supported by the fact that adding a capacitor in parallel with the varistor, which should also help dissipate the transient, reduced the crash frequency (though it still crashes after about 5 or 10 minutes of cycling).

To fully isolate the USB board from the rest of the system, I’ve ordered some optoisolators. Optoisolators chips that electrically isolate one circuit from another by coupling them with light. They have an LED driven by the input coupled to a phototransitor that forms the output. I’ll have them on Saturday, and with them I’ll be able to fully isolate the USB board from the high power switching circuitry. Hopefully that will fix our problems.

We’ve begun work on the PyroCardium sculpture, making a 6-foot-tall version with 1 Watt red LEDs to appear at False Profit Alchemy on April 26 at Cell Space. On the virtual side, the sculpture truss and helix is all modeled up in 3D using Rhino. On the physical side, the TIG welder is out, as is the metal bender, and the smaller truss is coming together.

Probably the most challenging aspect of building a swirly sculpture (aside from the dancing fire) is bending thick pieces of aluminum on all 3 axes. Dyche has come up with a pretty ingenious method. Our first helix will be comprised of seven semi-circles, of successively smaller diameter. Each piece of aluminum stock is placed in the metal roller at angle, so it gets bent in a semi-circle in one dimension, and pulled upward out of the circle’s plane as well. When these pieces connect together, the decreasing diameter is what gives the sculpture its skewed shape.

False Profit Labs has received grants from Burning Man for both The Hydrogen Economy and PyroCardium. We’re honored and really excited. Even though we’ve come a long way on the projects, there is much work to be done. I think that along with these grants comes the responsibility to deliver, and to bring what we’ve promised in our proposals to life out on the playa.

Since we had to put the proposals online quickly for this week’s Jack Rabbit Speaks (JRS), I dumped images out of the proposal PDF files and made these online versions.

The Hydrogen Economy
PyroCardium

I didn’t have much luck with the PDF to HTML conversion tools, so if you know of a good one, please post it.