The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Improvements

Making the world a better place, one piece at a time

Copying Video Files From Action Cameras to a NAS Drive

For unknown reasons, a recent VLC update caused it to ignore uppercase file extensions: MP4 and AVI files no longer appear in its directory listings, while mp4 and avi files do. The least-awful solution involved renaming the files after copying them:

find /mnt/video -name \*AVI -print0 | xargs -0 rename -v -f 's/AVI/avi/'
find /mnt/video -name \*MP4 -print0 | xargs -0 rename -v -f 's/MP4/mp4/'
find /mnt/video -name \*THM -print0 | xargs -0 rename -v -f 's/THM/thm/'

Yup, that scans the whole drive every time, which takes care of stray files, manual tweaks, and suchlike. The THM files are useless thumbnails; I should just delete them.

While I had the hood up, I listed the remaining space on the NAS drive and cleaned up a few misfeatures. I manually delete old video files / directories as needed, usually immediately after the script crashes for lack of room.

The Sony HDR-AS30V can act as a USB memory device, but it dependably segfaults the ExFAT driver; I now transfer its MicroSD card to an adapter and jam it into the media slot on the monitor, where it works fine.

Protip: always turn the AS30V on to verify the MicroSD card has seated correctly in its socket. Unfortunately, the socket can also hold Sony’s proprietary Memory Stick Micro cards (32 GB maximum capacity = roadkill), but the dual-use / dual-direction socket isn’t a snug fit around MicroSD cards. You (well, I) can insert a card so it looks fine, while sitting slightly canted and not making proper contact. The camera will kvetch about that and it’s easier to fix with the camera in hand.

I’ve disabled USB device automounting, as I vastly prefer to handle them manually, so the script asks for permission in order to mount the drives. The transfer requires about an hour, so I’ve extended the time the sudo password remains active.

The script lets both cards transfer data simultaneously; the Fly6 generally finishes first because it produces less data. That produces a jumbled progress display and the script waits for both drives to finish before continuing.

The Bash source code as a GitHub Gist:

	#!/bin/sh
	thisdate=$(date –rfc-3339=date)
	echo Date is $thisdate
	date
	# MicroSD cards not automounted
	as30v=/mnt/AS30V
	fly6=/mnt/Fly6
	sudo mount -o uid=ed /dev/sdb1 /mnt/AS30V/
	sudo mount -o uid=ed /dev/sdc1 /mnt/Fly6/
	# IOmega NAS defined as /mnt/video in fstab
	sudo mount /mnt/video
	mkdir /mnt/video/$thisdate
	rsync -ahu –progress $as30v/MP_ROOT/100ANV01/ /mnt/video/$thisdate &
	pid1=$!
	rsync -ahu –progress $fly6 /mnt/video
	date
	rc2=$?
	echo Fly6 RC is $rc2
	echo Waiting for $as30v
	wait $pid1
	rc=$(( $rc2 + $? ))
	date
	echo Overall RC: $rc
	if [ $rc -eq 0 ] ; then
	echo Fix capitalized extensions
	find /mnt/video -name \*AVI -print0 \| xargs -0 rename -v -f 's/AVI/avi/'
	find /mnt/video -name \*MP4 -print0 \| xargs -0 rename -v -f 's/MP4/mp4/'
	find /mnt/video -name \*THM -print0 \| xargs -0 rename -v -f 's/THM/thm/'
	echo Space remaining on NAS drive:
	df -h /mnt/video
	echo Remove files on AS30V
	rm $as30v/MP_ROOT/100ANV01/*
	echo Unmount cards and NAS
	sudo umount $as30v
	sudo umount $fly6
	sudo umount /mnt/video
	else
	echo Whoopsie: $rc
	fi

view raw savevideo.sh hosted with ❤ by GitHub

2017-05-19

AD8310 Log Amp Module: Video Bandwidth Rolloff

The part I didn’t understand turned out to be the bandwidth of the final output stage = “video bandwidth”, which defaults to 25 MHz. After fixing the input circuitry, a 25 MHz VBW let the output track a 60 kHz input signal just fine:

AD8310 – modified – 60 kHz 1Vpp

Adding a 56 nF cap across the C6 terminals (just above the AD8310) lowered the VBW to about 1 kHz:

AD8310 Log Amp module – VBW rolloff cap

Which flattened that sucker right out:

AD8310 – 1 kHz VBW cap – 60 kHz 1.394 V

The ripple for an absurdly high amplitude 32 kHz signal amounts to 36 mV:

AD8310 – 1 kHz VBW cap – 32 kHz – VBW ripple

Firing the tracking generator into the input with a frequency sweep from 100 kHz to 250 MHz shows the low end looks much better:

AD8310 – 1 kHz VBW cap – 100 kHz 250 MHz – 0 dB atten

There’s a slight droop across the sweep that might amount to 50 mV = 2 dB, which I’m inclined to not worry about in this context.

Applying the attenuators once again produces a scale factor of 23.5 mV/dB across 30 dB of RF, but this time the 60 kHz output makes sense, too.

Using the typical output curve from AN-691, that 2.0 V output corresponds to -13 dBm, which sounds about right for the tracking generator (which might really be -10 dBm).

I must calibrate the log amp output to find the actual intercept point (nominally -95 dBm, but could range from -86 to -102) at 60 kHz. The intercept is the extrapolated RF input producing 0 V out, which then acts as an offset for the voltage-to-dBm calculation; you start by finding the slope of the voltage vs. dBm line at some convenient power levels, then solve for dBm with V=0.

So a cheap AD8310 Log Amp module from eBay can work in the LF band, after you rearrange the input circuitry and tweak the chip’s filters. At least now I have a better understanding of what’s going on …

2017-05-17
AD8310 Log Amp Module: Corrected Input Circuit

After puzzling over the AD8310 Log Amp module’s peculiar frequency response, I hacked up the front end circuitry to match the data sheet’s recommended layout:

AD8310 Log Amp module – revised

Given the intended LF crystal-measurement application, a hulking 51 Ω metal film resistor sprawled across the ground plane will work just fine. All three ceramic caps measure a bit under 1 µF; I intended to solder the input caps atop the existing 10 nF caps, but that didn’t work out well at all.

I should harvest the InLo SMA connector to prevent anyone from mistaking it for an actual input.

With that in place, the log amp output makes more sense:

AD8310 – modified – 100 kHz 150 MHz – 0 dB atten

That trace tops out at 150 MHz, not the previous 500 MHz, but now the response is flat all the way out. The log amp generates plenty of hash when the tracking generator isn’t producing a valid signal.

The 60 kHz response looks different:

AD8310 – modified – 60 kHz 1Vpp

So it’s really the log amp response to the absolute value of the sine wave (or, more accurately, to the sine wave re-zeroed around Vcc/2), with minimum output at the input’s zero crossings. At 500 mV/div, the log amp says the input varies by 42 dB = 1000 mV/(24 mV/dB), which might actually be about right for a zero-crossing (or zero-approaching absolute value of a) signal; logarithms don’t deal well with zeros.

The AD8310 datasheet and AN-691 suggest the 2.5 V output corresponds to +10 dBm = 12.5 Vrms input, which flat-out isn’t the case. However, the actual 500 mVpeak = 350 mVrms input is 2.5 mW = +4 dBm, so maybe it’s within spitting distance of being right.

AN-691 recommends 10 µF input caps for “low frequency” use, showing results down to 20 Hz; 1 µF seems to get the circuit close enough to the goal for use near 60 kHz.

It also recommends a cap on the BFIN pin (pin 6) to reduce the output stage bandwidth = “video bandwidth” and improve the overall accuracy, which remains to be done. The datasheet suggests rolling VBW off at 1/10 the minimum input frequency, which would be around 3 kHz for use with 32.768 kHz crystals. The equation, with reference to the internal 3 kΩ bias resistor:

C_FILT = 1/(2π 3 kΩ VBW) – 2.1 pF = 18 nF

For a bit more margin, 1 kHz would require 56-ish nF.

The PCB has a convenient pair of pads labeled C6 for that capacitor. This may require protracted rummaging in the SMD capacitor stash.

Rolling off the VBW should reduce the hash on the 100 kHz end of the frequency sweep and filter the 60 kHz response down to pretty much a DC level.

Applying the 10 dB and 20 dB SMA attenuators to the input from the tracking generator and recording the log amp output voltage produces this useful table:

AD8310 Log Amp – mods and log response

With the terminating resistor on the correct side of the input caps, the log amp seems to be working the way it should, with an output varying a bit under the nominal 24-ish mV/dB over a 30 dB range.

We need caps! Lots of caps!

A quick search with the obvious keywords suggests nobody else has noticed how these modules work over a reasonable bandwidth. Maybe I’m the first person to use them in the LF band?

2017-05-16
Zire 71 Protector: Some Things Last

This ABS slab emerged from the Thing-O-Matic in early 2012:

Zire 71 protector in place

The Zire would power on whenever the switches clicked or that little joystick moved, which happened regularly enough to be annoying.

Mary made a small case that matched the other pouches I carry around:

Belt pack – camera case – PDA case

She made the case to fit an HP48 calculator, but it was close enough for the Zire.

Time passed, the Zire died, I started carrying a Kindle Fire in another pocket, but the ABS slab provided a convenient stiffener between some Geek Scratch Paper and the various pencils / pens / markers / screwdrivers / flashlight filling the available space.

Unfortunately, minus the backup of an electronic slab, the protector finally failed along an obvious stress riser:

Zire 71 protector – cracked

I cut a similar rectangle from a sheet of unknown flexy plastic, rounded the corners, clipped the pencils & whatnot to it, and maybe it’ll survive for a while.

2017-05-13
XTC-3D Epoxy Coating: Results

Having figured the mixing ratios, found the mixing trays, and donned my shop apron, I buttered up several iterations of the badge reel case to see how XTC-3D epoxy works on the little things around here.

In all cases, I haven’t done any sanding, buffing, or primping, mostly because I’m not that interested in the final surface finish.

A single coat produces a glossy finish with ripples from the printed threads:

XTC-3D – Hilbert – reflective

Seen straight on, without the glare, a little speck toward the lower right corner shows that cleanliness is next to impossible around here:

XTC-3D – lines – direct

An additional coat atop a Hilbert-curve upper surface comes out somewhat smoother:

XTC-3D – Hilbert – reflective 2

Another view, with less glare, shows the pattern a bit better:

XTC-3D – Hilbert – reflective 1

With no glare, the 3D Honeycomb infill shows through the surface:

XTC-3D – Hilbert – direct

Coating the surface with epoxy definitely makes it more transparent / less translucent by filling in the air gaps.

The sides of that part have only one coat and still show typical 3D printed striations.

Three coats wipe out the striations, along with all other surface detail:

XTC-3D – Bezel – front oblique

The bolt head recesses collected enough epoxy to require reaming / milling, which certainly isn’t what you want in that situation. The bolt holes also shrank, although my usual hand-twisted drill would probably suffice to clear the epoxy.

Another view shows a glint from the smooth surface filling the upper-right recess:

XTC-3D – Bezel – front

Three coats definitely hides the 3D printed threads, although you can see some ridges and edges:

XTC-3D – heavy – oblique

The epoxy isn’t perfectly self-leveling, probably due to my (lack of) technique:

XTC-3D – heavy – reflection

Blowing out the contrast shows the surface finish:

XTC-3D – heavy – direct – boost

Those scratches come from fingernails, after the overnight curing time. The surface is hard, but not impervious to scratching, which is about what you’d expect for a clear epoxy.

Slightly over-thinning the XTC-3D with denatured alcohol in a 0.7 : 0.3 : 0.3 by weight ratio produced a watery liquid that penetrated directly into the surface:

XTC-3D – thinned – oblique

The finish depends critically on what’s below the surface and how much epoxy you apply. I tried to spread it uniformly with a foam brush, but the center came out somewhat rougher than the outer edge:

XTC-3D – thinned – oblique

The striations along the sides filled in a bit, but surely not enough to satisfy anybody who worries about such things.

A specular reflection shows the changing surface smoothness:

XTC-3D – thinned – oblique reflective

Perhaps two coats of thinned epoxy would produce a watertight / airtight part, without changing the overall dimensions by very much. The mechanical properties depend almost entirely on the plastic-to-plastic bond, so I doubt a thin epoxy layer would improve its pressure-handling capabilities.

Few of the parts I make will benefit from an epoxy coating and I definitely don’t want to get into post-processing the parts just to improve their looks!

2017-05-09
Wearable LED vs. Astable Multivibrator vs. Dead Lithium Cells

Mashing the wearable LED from the completely dead CR2032 cell with a classic astable multivibrator circuit and a not-dead-yet CR123 cell produced a pure-analog desktop blinky:

CR123A Astable – front

Of course, I managed to swap the base resistors, which meant the LED stayed on most of the time, which accounts for the slightly off-kilter brown resistor just under the LED.

It doesn’t look like much with the LED off:

CR123A Astable – top – off

Running from a 2.8 V (= dead) lithium cell, the LED lights a dark room at 3 mA:

CR123A Astable – top – on

The LTSpice schematic gives the details:

Astable Multivibrator – CR2032 – schematic

The LED definitely didn’t come from Nichia and the 2N3704 transistors aren’t the 2N3904s found in the LTSpice library, but, by and large, this is the kind of circuit where nearly anything will work.

The actual LED current obviously depends critically on the particular LED and the cell voltage, so this represents more of a serving suggestion than an actual prediction:

Astable Multivibrator – CR2032 – waveform

Indeed, a Tek current probe clamped around one of those 10 AWG copper wires shows a much more enthusiastic LED current (1 mA/div):

Astable – CR123A 2.8 V – 1 mA -green

I don’t trust the baseline very much. The simulation & back of the envelope agree: the LED-off current should be around 400 µA (which doesn’t depend on the LED at all), so it’s in the right ballpark.

Your mileage will definitely differ.

It runs without a trace of software, which everybody at Squidwrench thought was wonderful …

2017-05-08
XTC-3D Epoxy Coating

The striations inherent in the DIY-grade 3D printing process don’t bother me all that much, but I got some XTC-3D epoxy to see what I’ve been missing. The impressive scrap pile from the badge reel holder provided test pieces:

XTC-3D Epoxy – test pieces – holders

If I were serious, I’d figure out a better way to hold the parts. For now, I jammed a watch crab into the back and trapped the bezel on a watch holder, but … ick.

Weighing the components seems the least-awful way to get the small quantities I need. The instructions recommend 100:43 by weight of resin (A) : hardener (B):

XTC-3D Epoxy – weighing pan

For these tiny parts, 2 g + 0.9 g was way too much and 1 g + 0.4 g seemed entirely adequate. If you slowly drool resin into the pan, drool slightly less than half that much hardener, and it’ll be about as close as you can get. The hardener is much less viscous than the resin: drool carefully.

The stuff might be self-leveling on larger parts, but on these small surfaces it’s better (IMO) to dry-brush multiple layers: you can see thicker and thinner sections in the first picture. The recoat time runs about 1-½ h.

The instructions recommend acetone or denatured alcohol as a thinning agent, at 10 to 25% of the resin volume, with curing times up to 24 h. Alcohol seems less likely to produce Bad Results, because it won’t evaporate instantly. Neither will affect PETG, but if you’re using another plastic, keep its solvent list in mind.

I tried alcohol with a by-weight amounts around 0.7 : 0.3 : 0.3 g, obviously overshooting both the hardener and the alcohol by a few drops. The end result resembled thick water, brushed on easily, and penetrated the surface easily.

A first coat of thinned epoxy should fill voids and unify the surface without changing the dimensions very much, with subsequent coats leveling the striations.

More pix after more layers and more curing …

2017-05-04