Kinkasan2
Hello,
Don’t know if anybody is still reading this. Last 3 weeks, last week especially, has been crazy. Hoping things will slow down, now that the testing at the proving grounds is over. We measured the pressure waveforms and rise times of blasts from different sizes of C4 plastic explosive, as well as rounds from a Striker (like a Tank, but on wheels) and an M1 Abrams. They let me keep a Striker shell. It’s taller than my knee. The cannon rounds were the loudest. At 100m, they felt like someone thumping you on the chest.
The only problem is, the C4 explosions leave enough stuff in the area that you can’t ever wear those clothes through an airport security again without getting detained. The army guys all laughed about it, (they can just show them their army card, or whatever), but sucks for the rest of us.
The 1MHz microphone I built actually worked, well… for the most part. Actually, it wasn’t the hardware that limited the performance, it was the electronics. This is weird because normally in microphone design, the diaphragm construction, not electronics, limit the bandwidth. But whatever. I didn’t have time to build a new amplifier for the signal, so I slapped one of these small signal amplifiers I had assembled for electrets earlier behind the mic. The stats for the chip said that at a gain of 10 the bandwidth was 1MHz. Problem is, I was exceeding the slew rate limit, which is how fast (in Volts per second) the output of one of these chips can change. So, all my rise time measurements were limited by the slew rate. Using it with the Oscilloscope, however, it still gave us a lower bound that was about 10X higher than we could get from the $50,000 data acquisition system/0.125” mic combination we were using for alternate measurements.
Brett, chum from Sendai, just sent me a bunch of photos from Kinkasan. These are all of them that he sent except… the snake photo. It seriously looked about a quarter as long as it really was. I just couldn’t bring myself to post it… hoping he’ll send me another that shows off it’s truly magnificent size 
Those deer and the water (with the cliffs) are increadible.
Matt
I think that a pair of clothes would defiantly be worth a day of C4 explosions.
-j
Matt – yeah we were hoping all around on those cliffs. The Deer were interesting cause even the adults had spots. Too bad I didn’t know about the place, until a few weeks before I left…
Jacob – It was. Completely. I’m not so worried about the clothes as getting detained in an airport (and missing my flight), because I got C4 on something I didn’t know I got it on. But yeah… and I’ll try to post a pic of the shell, too
Yay, you’re back!