Archive for March, 2012

Monthly Subconscious: Chandelier Spider

An odd critter control technique:

Curious chandelier spider

Curious chandelier spider

We generally capture and deport spiders, figuring that they’ll do much better outside than in. Judging from the collection of insect hulls under some of the webs, though, that may not be entirely correct.

For what it’s worth, we don’t even have a chandelier…

In text:

I wish damage on the curious chandelier spider.

 

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Panic Button Variations

Those panic buttons in the high school cafeteria still beg the question: who thought panic buttons would be a Good Idea? I recently served as a judge for the Science Fair qualification show and found some variations on the theme.

One seems in good shape, although I don’t know if it’s been repaired:

Intact panic button

Intact panic button

Several have missing buttons, but the innards seem intact:

Buttonless panic button

Buttonless panic button

In the event of an actual panic, I suppose you simply yank the cage off the wall:

Up-armored panic button

Up-armored panic button

I cannot imagine what logic justified protecting one button and leaving the others to the tender mercies of the student population.

Our tax dollars at work, for sure…

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Tea Ball Revivial: Redux

That tea ball (OK, infuser) hasn’t killed me yet, but it was looking rather grody despite a more-or-less monthly run through the dishwasher. So when Mary made up a bleach solution to sterilize her plant starting pots, I tossed it into the bottom of the pan for half an hour:

Bleached tea ball

Bleached tea ball

Zowie! All the organic schmutz vanished, leaving it as good-looking as new.

No before picture, alas, but maybe next time…

Memo to Self: Do that more often.

,

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DIY Vanilla Extract: Batch 2 On the Shelf!

After decanting the homebrew vanilla extract from those bottles, I added enough vodka to cover the spent beans, ran them through the blender, and drained the liquid:

Draining the vanilla dregs

Draining the vanilla dregs

It’s rather muddy and probably not worth keeping, but we’ll see what settles out:

DIY Vanilla dregs

DIY Vanilla dregs

The Good Stuff looked like this before it went into a dark corner of the Basement Laboratory Storage Warehouse:

DIY Vanilla Extract - Batch 2 Done

DIY Vanilla Extract - Batch 2 Done

It turns out you (well, I) cannot run vanilla extract through an ordinary coffee filter: it just doesn’t drain well at all. Cheesecloth didn’t seem worth the effort, so I combined all the clear liquid in a single jar, let it settle for a few days, then decanted it back into those three bottles again. The bottom of the rightmost bottle has a layer of what Breyers calls “real vanilla bean specks” in their ice cream.

In round numbers, $20 for half a pound of beans and $16 for a 1.75 l bottle of 80 proof vodka adds up to $36 for maybe 1.4 l of DIY vanilla extract = $26/l. Commercial vanilla extract runs about $72/l, so that’d be $100 in those bottles.

One could drive the DIY price down by processing more beans at a time, but this should keep us in vanilla for quite a while; that cup of hot cocoa in the afternoon smells really good now!

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Cassini Saturn Orbiter vs. Tin Whiskers

Although I don’t often block-quote other sources, for this I’ll make an exception:

The Cassini Plasma Spectrometer (CAPS, off since June 2011) was powered back on on March 16 based on the unanimous agreement of the review board at the CAPS turn-on review held on March 8. All went as planned for both the instrument and the spacecraft during the turn-on. The high rail to chassis short internal to the instrument that was part of what prompted it to be turned off last June was not present, and no changes were seen in the bus voltages or currents when the turn-on occurred. On Tuesday, March 20, the high rail to chassis short in the CAPS instrument returned, generating the same condition that existed at the time the instrument was turned off. However, based on the tin whisker model developed by the NESC team, this condition is believed to be understood and is not expected to cause any problems for either the instrument or the spacecraft. The CAPS instrument has been left powered on and is sequenced to operate as originally planned for the 75 kilometer Enceladus flyby coming up on March 27.

Having seen a forest of tin whiskers myself, that’s a pretty scary diagnosis. One assumes NASA takes extensive precautions, based on their experience, but … 15 years in hard vacuum and free fall will do odd things to spacecraft.

Remember those Toyota unintended acceleration problems? Guess what caused some of them: yup. Read their report to find out what makes metal whiskers so hard to detect. Hint: combine a minimum threshold voltage with a very low current capacity.

You could subscribe to the Cassini Significant Events newsletter.

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Gnuplot Datafile Formatting

The MOSFET tester spits out datasets using this tedious Arduino code:

void PrintHeader(void) {
  Serial.println();                         // Gnuplot group break
  Serial.println("#-----------------------------");
  Serial.print("# VGate: ");
  Serial.print(VGateSet,3);
  Serial.println();
  Serial.print("# TSetpoint: ");
  Serial.print(TSetpoint,1);
  Serial.println(" C");
  Serial.println("# VGS \tVDS \tID  \tRDS \tC   \tTime");
}

void PrintTempHeader() {
  Serial.println();                                    // Gnuplot index break
  Serial.println();
  Serial.print("#T=");                                //  ... index name
  Serial.println(TSetpoint,1);
  Serial.println("#=============================");
  Serial.print("# Setting temperature to: ");        // human-readable annotation
  Serial.print(TSetpoint,1);
  Serial.println(" C ...");
}

... later, deep inside the main loop ...

    Serial.print(VGateSet,3);
    Serial.print('\t');
    Serial.print(VDrainSense,3);
    Serial.print('\t');
    Serial.print(IDrainSense,3);
    Serial.print('\t');
    Serial.print((IDrainSense == 0.0) ? 0.0 : (VDrainSense / IDrainSense),3);
    Serial.print('\t');
    Serial.print(Temperature,1);
    Serial.print('\t');
    Serial.print(millis() - StartTime);
    Serial.println();

All that produces a text file formatted to work with Gnuplot, including a blank line between successive gate voltage groups to produce separate plot traces:

#T=0.0
#=============================
# Setting temperature to: 0.0 C ...

#-----------------------------
# VGate: 4.250
# TSetpoint: 0.0 C
# VGS 	VDS 	ID  	RDS 	C   	Time
4.250	1.200	0.000	0.000	1.0	1757
4.250	1.665	0.044	37.851	1.0	1861

#-----------------------------
# VGate: 4.500
# TSetpoint: 0.0 C
# VGS 	VDS 	ID  	RDS 	C   	Time
4.500	0.003	0.000	0.000	1.0	2038
4.500	0.016	0.044	0.370	1.0	2143
... snippage ...
4.500	0.212	1.953	0.108	0.9	6105
4.500	0.216	2.001	0.108	0.9	6210

Which produces a plot like this:

IRFZ44

IRFZ44

It’d be handy to automatically generate labels for the gate voltages, but I haven’t been able to figure out how to read values from the dataset and plunk them into the label strings. You can, however, select blocks of gate voltage and superblocks of temperature with a bit of effort.

The Bash script that feeds Gnuplot looks something like this:

#!/bin/sh
#-- set plot limits
tx=3
vgs_min="4.0"
vds_max="0.2"
rds_max=100
rds_tics=$((${rds_max} / 4))
id_max="2.0"
#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/"
base="${1%.*}"
echo Base name: ${base}
ofile=${base}.png
echo Output file: ${ofile}
#-- do it
gnuplot << EOF
#set term x11
set term png font "arialbd.ttf" 18 size 950,600
set output "${ofile}"
set title "${base}"
set key noautotitles
unset mouse
set bmargin 4
set grid xtics ytics
set xlabel "Drain-Source Voltage - VDS - V"
set format x "%4.2f"
set xrange [0:${vds_max}]
#set xtics 0,5
set mxtics 2
set ytics nomirror autofreq
set ylabel "Drain Current - ID - A"
set format y "%4.1f"
set yrange [0:${id_max}]
#set mytics 2
set y2label "Drain Resistance - RDS - mohm"
set y2tics nomirror autofreq ${rds_tics}
set format y2 "%3.0f"
set y2range [0:${rds_max}]
#set y2tics 32
#set rmargin 9
set datafile separator "\t"
#set label 1 "Temp index = ${tx}" at 0.81,0.55 font "arialbd,18"
set label 2 "VGS >= ${vgs_min} V" at 0.11,0.55 font "arialbd,18"
plot    \
"$1" using 2:((\$1 >= ${vgs_min})?\$3:NaN)            index $tx:$tx           with lines lt 3 lw 2 title "ID" ,\
""   using 2:((\$1 >= ${vgs_min})?(\$4*1000):NaN)    index $tx:$tx axes x1y2 with lines lt 4 lw 2 title "RDS"
EOF

The variables up near the top control the plot limits; it’d be nice to have a complex Bash script that prompted for values, had useful defaults, and fed all that into Gnuplot. Given what I’m doing, it’s easier to just keep the Bash script open in the portrait monitor, watch the results on the landscape monitor, and twiddle until it looks right.

This script produces a plot for a single temperature range based on the superblock index tx; you can select a single block using index name (along the lines of “T=0.0″), but you can’t select multiple such blocks in a single plot statement.

Selecting gate voltages requires testing the first column for a match with the trinary operator and assigning the data value for lines that don’t match to the not-a-number value NaN to prevent it from appearing in the plot:

((\$1 >= ${vgs_min})?\$3:NaN)

All in all, the whole apparat makes for a fairly brittle set of code, but the plots come out ready for printing and that makes up for a lot.

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CH-47 Flyover

I have no idea what’s going on around here any more…

CH-47 helicopter formation

CH-47 helicopter formation

Those northbound CH-47 Chinooks looked to be barely over treetop level, but the rotors are 60 feet in diameter and they were much higher than they seemed. Shook the house and brought all hands outside to watch the show.

I remember getting a tour inside one, a long time ago, at a military air show.

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