By turns: tinker, engineer, husband, author, amateur raconteur, recumbent cyclist, father, ham radio geek. So many projects, so little time!


JYE Tech DSO150 Oscilloscope: Build Notes

I did a quick build of a JYE Tech DSO150 oscilloscope to see how it’d work in a proposed Squidwrench advanced soldering class / kit build session.

The main board requires adding only a few switches and headers, then removing a 0 Ω jumper resistor:

DSO150 - main board - bottom

DSO150 – main board – bottom

The analog board requires a handful of 1/8 W resistors, various capacitors, switches, and the BNC connector:

DSO150 - main board - front

DSO150 – main board – front

Some (lightly edited) color commentary from my summary email:

  • Just finished assembling the kit, which required two hours; I’m admittedly fussy. The one joint I missed on the input coupling switch required a complete disassembly, but all the rest worked fine.
  • The UI is much better than the DSO138.
  • Soldering the BNC connector requires lots of heat. My ordinary Hakko iron had inadequate grunt, so I deployed the hulking Radio Shack 150 W gun and did the job in seconds.
  • The resistors require a meter to measure them during installation, because they’re 1% 1/8 W jobbies with many teeny color strips in Chinese tints you’ve never seen before. I could not sort them visually, even with a lighted headband magnifier, and I know what I’m looking for.
  • The caps are marked, but using a meter builds confidence.
  • And, yes, the kit had all the right parts and they all worked. The instructions call for powering up the main board before starting assembly, then again after removing a 0 Ω jumper resistor, but that’s the extent of the “testing” required.
  • They recommend a flush cutter and I’d say it’s pretty much required. An ordinary diagonal cutter won’t get close enough to the PCB.
  • I needed an angle-tip tweezer to lay the PCB screws in place.
  • Don’t install the knob until the very last step and maybe wait until you’ve verified all the functions. You have been warned.
  • The minimum power supply voltage really is 8.0 V, not the 7.4 V from a not-quite-fully-charged pair of lithium cells. A 9 V alkaline battery will last a few minutes. A noisy boost converter / crappy 9 V wall wart translates directly into noise on the display, particularly on the internal calibration signal.
  • The “0.1 V” calibration signal turned out to be 150 mV, as measured on a real scope, at 1 kHz. The 3.3 V signal is closer to reality. Both are noisy from a noisy supply.
  • All in all, it’s a pretty good scope for thirty bucks!
  • Newbies will find it a challenging three hour build, for sure.

The next step involves adding a case and battery power:

DSO150 battery hack - first light

DSO150 battery hack – first light


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Imagemagick 6 vs. PDF

Come to find out Xubuntu 18.04 ratcheted the ImageMagick security settings up to a dangerous chattering whine:

convert p???.jpg "Machining D-bit Drills.pdf"
convert-im6.q16: not authorized `Machining D-bit Drills.pdf' @ error/constitute.c/WriteImage/1037.

Fortunately, someone who understands this stuff encountered the problem before I did and posted a great description of the solution.

To forestall link rot, the process looks like:

cd /etc/ImageMagick-6/
sudo cp policy.xml policy.xml.base
sudo nano policy.xml
… change one line …
 policy domain="coder" rights="read|write" pattern="PDF"

It is completely unclear to me whether ImageMagick (as of ImageMagick 6.9.7-4 Q16 x86_64 20170114 ) requires or merely tolerates the vertical bar in place of commas, nor whether it’s in my best interest to replace "coder" with "*".

In any event, I can once again stuff bitmap images into PDF files.


Ants in My Drawers

Our Compact Edition of the OED doesn’t get much use these days, but Mary needed a magnifier for a class on quilt judging and the OED has one that seemed just about right:

OED Magnifier Box in drawer

OED Magnifier Box in drawer

The magnifier comes in a removable box fitted neatly into the drawer, revealing a surprise underneath:

OED Magnifier drawer - plastic ant

OED Magnifier drawer – plastic ant

A detail view:

OED Magnifier drawer - plastic ant - detail

OED Magnifier drawer – plastic ant – detail

It’s a plastic ant from a bag in the Kiddie Surplus box my Shop Assistant grew up with and a pleasant reminder of long-ago days, carefully placed where only I’d ever see it.

Of course, it’s still there …


Monthly Science: Motel Water Pressure vs. Height

Being a sucker for infrastructure and numbers, the fire sprinkler system pressure gauges in the motel stairwell proved irresistible.

The first floor gauge shows a nice round 100 psi:

Hotel water pressure - floor 1

Hotel water pressure – floor 1

Up on the second floor, it’s 90 psi:

Hotel water pressure - floor 2

Hotel water pressure – floor 2

With a different brand of gauge, it’s also 90 psi on the third floor:

Hotel water pressure - floor 3

Hotel water pressure – floor 3

Maybe 85 psi on the fourth:

Hotel water pressure - floor 4

Hotel water pressure – floor 4

Squinting at the parallax, call it 80 psi on the fifth:

Hotel water pressure - floor 5

Hotel water pressure – floor 5

At the top of the vertical pipe on the fifth, on the other side of a valve, we return to the original valve company at 78 psi:

Hotel water pressure - floor 5 - top

Hotel water pressure – floor 5 – top

Water weighs just over 62 lb/ft³ at room temperature, which works out to 0.43 lb/in² per vertical foot. Not having packed my laser distance widget, I’ll guesstimate 12 feet and 5 psi per floor.

A quick graph with an eyeballometric straight-line fit:

Motel sprinkler water pressures

Motel sprinkler water pressures

Call it 0.42 psi/ft, which is pretty close to the right answer.


Astable Multivibrator vs. Charged NP-BX1 Lithium Battery

Hitching a charged, albeit worn, NP-BX1 lithium battery to the astable multivibrator produces a blinding flash:

NP-BX1 Holder - SMT pogo pins

NP-BX1 Holder – SMT pogo pins

The current pulse shows the wearable LED really takes a beating:

Astable - NP-BX1 4V - 100mA-div

Astable – NP-BX1 4V – 100mA-div

The current trace is at 100 mA/div: the pulse starts at 400 mA, which seems excessive even to me, and tapers down to 200 mA. It’s still an order of magnitude too high at the end of the pulse.

On the other paw, maybe a 14% duty cycle helps:

Astable - NP-BX1 4V - base V - 100mA-div

Astable – NP-BX1 4V – base V – 100mA-div

The top trace shows the base drive voltage dropping slightly, although I suspect the poor little transistor can’t take the strain.

The LED really does need a ballast resistor …

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Sony NP-BX1 Battery Holder: SMT Pogo Pin Contacts

The original camera battery test fixtures used contact pins conjured from hulking gold-plated connector pins and coil springs:

Canon NB-6L holder - contact pin detail

Canon NB-6L holder – contact pin detail

The Sony HDR-AS30V camera chewed up and spat out a handful of batteries, all tested in the NP-BX1 test fixture:

NP-BX1 Holder - show layout

NP-BX1 Holder – show layout

Nowadays, SMT pogo pins produce a much more compact holder, so I figured I could put all those batteries to good use:

NP-BX1 Holder - SMT pogo pins

NP-BX1 Holder – SMT pogo pins

That’s the long-suffering astable multivibrator, still soldered to its CR123A holder.

Obviously, the battery holder should grow ears to anchor the 14 AWG copper posts and would look better in black PETG:

NP-BX1 Battery Holder - 1.5mm pins - solid model

NP-BX1 Battery Holder – 1.5mm pins – solid model

The battery lead wires get soldered to the ends of the pogo pins and are recessed into the slot in the end of the fixture. I used clear epoxy to anchor everything in place.

Fits perfectly and works fine!

The OpenSCAD source code as a GitHub Gist:


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Makergear M2 V4 Nozzle: More Silicone!

A Makergear forum discussion on PETG hair and the prevention thereof prompted me to take a look at the silicone coating I’d applied to the nozzle:

M2 - nozzle silicone - applied

M2 – nozzle silicone – applied

That was ten months ago. This is now:

M2 Nozzle - worn silicone coat

M2 Nozzle – worn silicone coat

The camera sees the nozzle in a mirror laid flat on the platform, making the image less crisp than a direct view.

So the silicone seems a bit worn around the tip, has acquired a few firmly adhered globs, and definitely isn’t as shiny.

Rather than (try to) peel it off and reapply a new coating, I picked off the globs, cleaned around the nozzle, and slobbered a thin layer atop the existing silicone:

M2 Nozzle - more silicone

M2 Nozzle – more silicone

Extruding a few millimeters of filament pushed the film off the nozzle opening and it now works as well as it ever did.