Mint Extract: Results

Six weeks later, the mint seemed about as extracted as it was going to get and I now have nearly a liter of decidedly green mint extract:

Mint Extract - liquid color

Mint Extract – liquid color

Correspondingly, the leaves turned from bright green to dull brown:

Mint Extract - spent leaf colors

Mint Extract – spent leaf colors

The smaller and darker pile in the rightmost bowl came from the smaller jar (on the left) with a higher alcohol-to-leaf ratio:

Mint Extract - start - 2018-05-29

Mint Extract – start – 2018-05-29

Perhaps packing the jars before pouring in the alcohol doesn’t extract as efficiently. Or maybe, as in so many things, it doesn’t really matter.

A liter of mint extract may not be a lifetime supply, but it’ll suffice for quite a while!


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Tek A6302 Current Probe: Reason for Being

The question occasionally comes up as to why one would want a Tektronix A6302 Hall effect current probe and AM503 amplifier. The answer is simple: non-contact, essentially non-invasive current monitoring.

I used the venerable dead-battery Astable Multivibrator to check out the rebalanced A6302 probe:

Tek A6302 Current Probe vs Astable Multivibrator

Tek A6302 Current Probe vs Astable Multivibrator

The scope screen in the background shows the two base voltages at the top, plus the overall battery current along the bottom:

Tek A6302 - Astable multivibrator - LED current 1 mA-div

Tek A6302 – Astable multivibrator – LED current 1 mA-div

The current at 1 mA/div shows plenty of noise, but the 200 ms LED pulse is barely 1 mA tall. The two AA alkaline cells have faded to 2.5 V, so the “wearable” white-LED-with-dyed-overcoat runs far under its nominal 3.6-ish V spec.

There’s basically no other way to get that result, because inserting a current-sense resistor into the circuit will alter the results, plus be intractably difficult to measure, particularly if you need the current in a non-ground-referenced branch of the circuit.

The AM503 has terrible thermal drift, by contemporary standards, but after the first half-hour or so it’s manageable for short durations. I’m thinking of epoxying a small knob to the screwdriver-adjustable twiddlepot to simplify the baseline adjustment.

Alas, even non-working probes and amps have become eBay collectables. You could, of course, buy new.

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Tek A6302 Current Probe: Offset Resistor Tweakage

A package deal of two Tektronix A6302 current probes arrived from eBay, with one probe having a small crack across its case (shown in the description and bought accordingly).

The other probe worked fine and was quite clean inside:

A6302 B055461 - major sections

A6302 B055461 – major sections

The cracked one couldn’t be balanced, with the twiddlepot on the AM503 amp unable to bring the signal down to 0 V from a positive offset on any of the ranges.

The current transformer might have suffered some stress on the upper-left corner of the main part (in the probe body), but it doesn’t have any obvious damage:

A6302 B032444 - ball - current transformer in place

A6302 B032444 – ball – current transformer in place

The small ball to the left of the transfomer lid provides the slide detent. It’s an ordinary 3/32 = 0.94 inch bearing. Which, as it happens, is a Good Thing, because there’s another one exactly like it somewhere in the litter under the Electronics Workbench.

Protip: follow the disassembly procedure in the instruction manual and do it over a towel or, at least, a shallow dish. You have been warned.

Extracting the transformer from the body revealed a numeric value I didn’t recognize at the time:

A6302 B032444 - current transformer

A6302 B032444 – current transformer

The top slide contacts looked awful, but they’re actually covered in semi-dried contact grease and cleaned up easily:

A6302 B032444 - slide contacts

A6302 B032444 – slide contacts

Swapping the “bad” transformer into the P6302 probe I got a while ago showed it wouldn’t balance, either, but the offset was far off into negative voltages. Putting the “good” transformer into the “bad” probe produced a similar too-positive offset. Conclusion: the transformer was probably good and Something Else was wrong.

Spending more time with the manuals produced this hint in the AM503 Amplifier circuit description:

AM503 manual - Hall offset - probe resistor selection

AM503 manual – Hall offset – probe resistor selection

Fortunately, the AM503 probe connector has pin labels:

Tek AM503 Amplifier - Probe Connector - pin ID

Tek AM503 Amplifier – Probe Connector – pin ID

Note the absence of pins G and I, probably to eliminate any confusion with “ground” and “one”, respectively.

Continuity checking reveals the left end of the 34.8 kΩ resistor connects to pin H:

A6302 B032444 - PCB 34.8k offset R

A6302 B032444 – PCB 34.8k offset R

Huh. Even a blind pig occasionally finds a truffle: where have we seen that value before? Apparently Tek measured each transformer / Hall sensor and wrote the appropriate offset resistor value exactly where it’d do the most good.

Although I don’t pretend to know why the transformer offset has changed, if Tek can select a resistor to correct the offset, so can I:

A6302 B032444 - PCB - tweaked 82k offset R

A6302 B032444 – PCB – tweaked 82k offset R

The 82 kΩ value roughly centers the offset twiddlepot span around 0 V; it’s the result of a binary search through the resistor drawers, rather than a complex calculation.

With the resistor in place and the probe reassembled in reverse order, everything works the way it should:

Tek A6302 - 82k ohm offset - 50 mA

Tek A6302 – 82k ohm offset – 50 mA

The lower trace is a square wave from the scope’s arb waveform generator into a (likely counterfeit) Fotek DC-DC solid-state relay, with the bench supply dialed to 5.7 V to put 5 V across a hulking 100 Ω power resistor, thus 50 mA through the probe. The purple trace comes from the repaired probe, with the other one turned off for pedagogic purposes:

Tek A6302 Calibration Setup

Tek A6302 Calibration Setup

That wasn’t easy, but seems to solve the problem.

Dang, I loves me some good Tek current probe action …



Ortlieb Backroller Pack Drop

Although the pair of Ortlieb Back-Roller packs on Mary’s bike make her look like a long-distance tourist, we’re actually on our way to her garden plot:



The left-side pack suddenly seemed unusually floppy:



One second later:



Another second and it’s visible under my right hand:



The view from her bike at about the same time:



I’m expecting to fall to my right, but it’d have been better if I hadn’t kicked the bag:



The pack went under the rear wheel and out the far side:



Where it came to rest in the middle of the trail:

Ortlib pack drop - aftermath

Ortlib pack drop – aftermath

Elapsed time from the first picture: just under 5 s.

Did you notice the other cyclist in the other pictures? She’s why I veered so hard to my right!

A pair of these latches hold the pack onto the rear rack:

Ortlieb pack drop - QL latch detail

Ortlieb pack drop – QL latch detail

When they’re properly engaged, they look like this:

Ortlieb pack drop - QL latch - secure

Ortlieb pack drop – QL latch – secure

When they’re not, they look like this:

Ortlieb pack drop - QL latch - whoopsie

Ortlieb pack drop – QL latch – whoopsie

Which is obvious in the picture and inconspicuous in real life.

The strap emerging from the top of the latch serves as both a carrying handle and latch release: pull upward to open the latches and release them from the bar, lift to remove the pack, and carry it away as you go. Installing the pack proceeds in reverse: lower the pack onto the rack bar, release the handle, and the latches engage.

Unless the pack is empty enough to not quite fully open the latches as you carry it, in which case the closed latches simply rest on the bar. We’ve both made that mistake and I generally give her packs a quick glance to ensure sure they’re latched. In this case, the plastic drawer atop the racks (carrying seedling pots on their way to the garden) completely concealed the pack latches.

Tree roots have been creasing the asphalt along that section of the rail trail: the bike finally bounced hard enough to lift the drawer and fall off the rack rod.

Memo to Self: In addition to the visual check, lift the packs using the strap across the middle holding the rolled-down top in place. Remember, don’t check by lifting the carrying handle, because it just releases the latches; another easy mistake to make.




Copying Action Camera Video: Now With UUIDs

Having tired of manually decoding UDEV’s essentially random device names produced for the various USB action cameras and card readers, I put the device UUIDs in /etc/fstab and let the device names fall where they may:

UUID=B40C6DD40C6D9262	/mnt/video	ntfs	noauto,uid=ed 0 0
UUID=0FC4-01AB	/mnt/Fly6	vfat	noauto,nodiratime,uid=ed	0	0
UUID=0000-0001	/mnt/M20	vfat	noauto,nodiratime,uid=ed	0	0
LABEL=AS30V	/mnt/AS30V	exfat	noauto,nodiratime,uid=ed	0	0

You get those by plugging everything in, running blkid, and sorting out the results.

The 64 GB MicroSD card from the Sony AS30V camera uses Microsoft’s proprietary exfat file system, which apparently doesn’t associate a UUID/GUID with the entire device, so you must use a partition label. The Official SD Card Formatter doesn’t (let you) set one, so:

exfatlabel /dev/sdd1 AS30V

It turns out you can include spaces in the partition label, but there’s no way to escape them (that I know of) in /etc/fstab, so being succinct counts for more than being explanatory.

One could name the partition in the Windows device properties pane, which would make sense if one knew it was necessary while the Token Windows Laptop was booted with the card in place.

I think this is easier then trying to persuade UDEV to create known device names based on the USB hardware characteristics, because those will depend on which USB card / device / reader I use. I can force the UUIDs to be whatever I want, because they’re just bits in the disk image.

With all that in place, you plug in All. The. Gadgets. and run the script (as seen below). The general idea is to verify the bulk video drive mounted OK, attempt to mount each memory card and fire off a corresponding rsync copy, wait until they’re all done, tidy the target filenames, then delete all the source files to get ready for the next ride.

Funneling all three copies to a single USB hard drive probably isn’t the smartest thing, but the overall write ticks along at 18 MB/s, which is Good Enough for my simple needs. If the drive thrashes itself to death, I won’t do it again; I expect it won’t fail until well outside the 1 year limited warranty.

If any of the rsync copies fail, then nothing gets deleted. I’m a little queasy about automagically deleting files, but it’s really just video with very little value. Should something horrible happen, I’d do the copies by hand, taking great care to not screw up.

After all, how many pictures like this do we need?

Ed signalling on Raymond

Ed signalling on Raymond

The Bash script as a GitHub Gist:


Rt 376 at Red Oaks Mill: Re-repaving

For unknown reasons, NYS DOT milled away some of the newly laid asphalt north of Red Oaks Mill:

Rt 376 Red Oaks Mill - New Pavement Milling

Rt 376 Red Oaks Mill – New Pavement Milling

Then laid it down again:

Rt 376 Red Oaks Mill - New Pavement - 2018-06-14

Rt 376 Red Oaks Mill – New Pavement – 2018-06-14

As far as we can tell, there’s absolutely no difference, other than the opportunity for a huge longitudinal crack between the shoulder and the travel lane.

My guess: the contractor shorted them an inch of asphalt, got caught, and had to do it over again.

It’s only NYS Bike Route 9, so you can’t expect much in the way of bicycle-friendly design or build quality.


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Monthly Image: Maple Tree Fungus

Repaving the driveway truncated the roots of a maple tree and, this year, produced a handsome pair of fungii:

Fungus - top view

Fungus – top view

Seen from the side, they’re even more complex:

Fungus - side view

Fungus – side view

They’re firm and perfectly healthy, but the tree is likely doomed.