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.

Category: Science

If you measure something often enough, it becomes science

Six Gallon Can Lid Adapter to Platform Bird Feeder

A House Finch suffering from Finch Eye Disease prompted me to sterilize our feeder, which meant providing a temporary feeder to keep the birds flying. Having an abundance of lids from six gallon plastic cans / buckets, this made sense:

Can Lid Feeder - installed — Can Lid Feeder – installed

Which required an adapter betwixt pole and lid:

Can Lid Feeder - assembled — Can Lid Feeder – assembled

Which requires a bit of solid modeling:

Can Lid Platform Feeder Mount - solid model - bottom — Can Lid Platform Feeder Mount – solid model – bottom

The lids have a central boss, presumably for stiffening, so the model includes a suitable recess:

Can Lid Platform Feeder Mount - solid model - support structure — Can Lid Platform Feeder Mount – solid model – support structure

As usual, automatically generated support fills the entire recess, so I designed a minimal support structure into the model and cracked it out with very little effort:

Can Lid Feeder - support structure — Can Lid Feeder – support structure

The tangle off to the right comes from a bridge layer with a hole in the middle, which never works well even with support:

Can Lid Platform Feeder Mount - Slic3r - bridge layer — Can Lid Platform Feeder Mount – Slic3r – bridge layer

Didn’t bother the birds in the least, though, so it’s all good.

I loves me my 3D printer …

The OpenSCAD source code as a GitHub Gist:

	// Adapter from steel pole to 5 gallon plastic can lid
	// Turns the lid into a improvised platform feeder
	// Ed Nisley – KE4ZNU – 2018-11

	Layout = "Build"; // Show Build

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	Protrusion = 0.1; // make holes end cleanly

	// Sizes

	ID = 0;
	OD = 1;
	LENGTH = 2;

	Wall = 10; // minimum thickness or width for anything

	Boss = [15,50,9]; // central boss on lie
	Flange = [50,110,Boss[LENGTH] + Wall];

	echo(Boss);
	echo(Flange);

	Pole = [(23.5 + 4*HoleWindage),26,45]; // small end of steel pole

	Screw = [5.0,8.0,25.0]; // 5 mm or 10-32
	ScrewOC = 80; // lid mounting screws
	NumScrews = 3;

	NumSides = NumScrews24;
	$fn = NumSides;

	//———————-
	// Useful routines

	module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes

	Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
	FixDia = Dia / cos(180/Sides);
	cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
	}

	//———————-
	// Build it

	module Bracket() {

	difference() {

	union() {
	rotate(180/(NumSides/2)) {
	cylinder(d=Flange[OD],h=Flange[LENGTH],$fn=NumSides/2); // fewer sides is OK
	cylinder(d=Pole[OD] + 2*Wall,h=Pole[LENGTH] + Flange[LENGTH],$fn=NumSides/2);
	}
	}

	translate([0,0,-Protrusion])
	rotate(180/NumSides)
	cylinder(d=Boss[OD],h=Boss[LENGTH] + Protrusion,$fn=NumSides);

	translate([0,0,-Protrusion])
	rotate(180/NumSides)
	cylinder(d=Pole[ID],h=2*(Pole[LENGTH] + Flange[LENGTH]),$fn=NumSides);

	for (i=[0:NumScrews-1])
	rotate(i*(360/NumScrews))
	translate([ScrewOC/2,0,-Protrusion])
	PolyCyl(Screw[ID],2*Flange[LENGTH],6);
	}

	}

	module Support() {

	NumRibs = NumSides/2;
	Rib = [0.95(Boss[OD] – Pole[ID])/2,2ThreadWidth,Boss[LENGTH] – ThreadThick];

	color("Yellow") {
	for (i=[0:NumRibs-1]) {
	a = i*360/NumRibs;
	rotate(a)
	translate([Pole[ID]/2 + Rib.x/2,0,Rib.z/2])
	cube(Rib,center=true);
	}
	rotate(180/NumSides)
	difference() {
	cylinder(d=Pole[ID] + 10ThreadWidth,h=1ThreadThick,$fn=NumSides);
	translate([0,0,-Protrusion])
	cylinder(d=Pole[ID],h=Rib.z + 2*Protrusion,$fn=NumSides);
	}
	}

	}

	if (Layout == "Show")
	Bracket();

	if (Layout == "Build") {
	Bracket();
	Support();
	}

view raw Can Lid Platform Feeder Mount.scad hosted with ❤ by GitHub

2018-12-11

JYE Tech DSO150 Oscilloscope vs. Actual Signals

The DSO150 oscilloscope’s specs give a 200 kHz bandwidth, so a 50 kHz sine wave looks pretty good:

DSO150 – sine wave 50 kHz 10 us-div

A 100 kHz sine wave looks chunky, with maybe 25 samples per cycle:

DSO150 – sine wave 100 kHz 10 us-div

The DSO150 tops out at 10 µs/div, so you can’t expand the waveform more than you see; 25 samples in 10 µs seems to be 2.5 Msample/s, exceeding the nominal 1 Msample/s spec. I have no explanation.

A 10 kHz square wave shows a blip just before each transition that isn’t on the actual signal:

DSO150 – square wave 10 kHz 20 us-div

At 50 kHz, there’s not much square left in the wave:

DSO150 – square wave 50 kHz 10 us-div

And, just for completeness, a 200 kHz square wave completely loses its starch:

DSO150 – square wave 200 kHz 10 us-div

A 10% (-ish) duty cycle pulse at 25 kHz has frequency components well beyond the scope’s limits, so it’s more of a blip than a pulse:

DSO150 – pulse 25 kHz 10 us-div

The pulse repetition frequency beats with the scope sampling and sweep speeds to produce weird effects:

DSO150 – pulse 25 kHz 100 us-div

Tuning the pulse frequency for maximum weirdness:

DSO150 – pulse 15 kHz 200 us-div

None of this is unique to the DSO150, of course, as all digital scopes (heck, all sampled-data systems) have the same issues. The DSO150’s slow sampling rate just makes them more obvious at lower frequencies.

Key takeaway: use the DSO150 for analog signals in the audio range, up through maybe 50 kHz, and it’ll produce reasonable results.

Using it for digital signals, even at audio frequencies, isn’t appropriate, because the DSO150’s low bandwidth will produce baffling displays.

2018-12-06
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

Up on the second floor, it’s 90 psi:

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

Maybe 85 psi on the fourth:

Hotel water pressure – floor 4

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

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

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

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

2018-12-01
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

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

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

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 …

2018-11-30
Squidwrench Electronics Workshop: Session 6 Whiteboards

Coverage of capacitors as charge-storage devices, rather than filters:

Session 6 – Whiteboard 1 – overview

We avoided all the calculus and derivations, taking the exponential waveform as a given for RC circuits:

Session 6 – Whiteboard 1 – exponential detail

Discussions of dielectrics, plate spacing / area, and suchlike:

Session 6 – Whiteboard 1 – dielectric permittivity

Some handwaving discussion of construction, electrolytic capacitor innards, and The Plague:

Session 6 – Whiteboard 1 – cap construction

A 1 F cap charged through a 1.8 kΩ resistor during most of the session to show what an 1800 s time constant looked like. Nope, it never quite got to the 3.5 V from the power supply, even when we all decided it was time to shut down!

2018-11-16
Monthly Image: AMP Plug Board

Around 1960, somebody my father knew at the Harrisburg AMP factory gave me a chunk of plugboard bandsawed from a scrapped computer or industrial controller, because he knew I’d enjoy it:

AMP Plug Board

He was right.

I spent months rearranging those little cubes (some with cryptic legends!) into meaningful (to me) patterns, plugging cables between vital spots, and imagining how the whole thing worked:

AMP Plug Board – detail

Long springs ran through the notches under the top of the blocks to connect the plug shells to circuit ground. The ends of the steel rails (still!) have raw bandsaw cuts, some of the blocks were sliced in two, the tip contact array behind the panel wasn’t included, and none of that mattered in the least.

Only a fraction of the original treasure trove survives. It was absolutely my favorite “toy” ever.

Quite some years ago, our Larval Engineer assembled the pattern you see; the hardware still had some attraction.

I’ve asked Mary to toss it in the hole with whatever’s left of me, when that day arrives …

2018-11-15
Bird Feeder Unbending

At some point in its history, the left rail holding the wood perch on our industrial-strength “squirrel proof” seed feeder took a hit, most likely from being dropped:

Squirrel on bird feeder

I finally got a Round Tuit and un-bent the poor thing:

Bird feeder – rail un-bending

Because the bend happened at the base of the vertical strut holding the shutter, I clamped a Genuine Vise-Grip sheet metal pliers along the straight section. The Craftsman knock-off Vise-Grip then applied torque at the bend, rather than just making things worse, and some two-axis tweakage lined up the rail pretty well.

With the bend taken care of, I clamped the rail in the bench vise with some scrap wood around the strut:

Bird feeder – warped rail

A percussive adjustment jam session flattened the top flange, leaving both sections as flat as they’re gonna get.

While I was at it, I turned a pair of stepped aluminum washers for the new wood rod:

Bird feeder – parting off washer

Which looked about like you’d expect, including a little chatter from the cut off tool:

Bird feeder – perch hardware

Yeah, I drilled the wood rod on the lathe, too; I loves me some simple lathe action.

Reassemble in reverse order and it’s all good:

Bird feeder – perch installed

We’re supposed to bleach the feeder every week to kill off the bacteria causing House Finch Eye Disease and, while I can’t promise a weekly schedule, we’ll (try to) reduce the amount of crud on the feeder this year.

If you’ve got a feeder, sign up for Project Feederwatch and do some citizen science!

2018-11-13