Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
This panel-mount LED indicator glued to the Z-axis stage of my Thing-O-Matic had been dutifully showing a bright green glow when the extruder heater was active:
Failed LED panel indicator
Of late, it began flickering erratically whenever the heater turned on. It used to flicker when the PID loop (hacked to be a bang-bang controller) drove the extruder temperature past the switching threshold, but this was worse.
It’s rated for 5 VDC, 25 mA and has an internal resistor to make that happen. Channeling the true spirit of DIY 3D printer electronics, I deliberately connected it directly across the 12 V extruder power and let it burn at 80 mA. The poor thing was surprisingly bright for an ancient green LED ( the 8124 date code stamped on the side I pried off for the picture says it’s three decades old) and, even under that abuse, it lasted for a year: not to be sniffed at.
I’d expect the LED to fail open when a bond wire burned through, but you just never can tell. It worked fine on the bench, which is typical of all intermittent failures.
So I popped an identical indicator off the stack, conservatively added a 270 Ω series resistor to drop the excess voltage, and it’s all good again.
Back in 2006, our ancient (19-ish years old) Whirlpool refrigerator started making weird howling noises suggested someone broke into the house and stuffed a dog inside the freezer. Turned out to be the fan behind the rear panel of the freezer compartment that moves air across the cooling coils and down into the refrigerator compartment; evidently the sintered bronze bearings wore just enough to let the shaft oscillate side-to-side while rotating.
I ordered a replacement, but then decided to try an old fix: put a dollop of STP in the bearings. That added enough damping to kill the resonance and let the old fan turn freely. It worked so well that I put the new fan on the shelf in case it came in handy later on.
Years passed… and then, as if by magic, the freezer dog reappeared.
Mary moved the contents to the downstairs chest freezer (she’s much more organized than I and wanted to find things again), I pulled the old fan out, installed the “new” fan, buttoned up the freezer, and it ran fine.
Whirlpool refrigerator fans
Until about two in the morning, when the freezer dog began howling again…
As nearly as I can tell, the new fan’s bearings arrived just slightly oversize; I doubt they’re pre-worn.
So I applied the STP fix to the new fan:
Remove the compression fitting from the fan blade hub
Remove the fan blades from the shaft
Remove the screws & nuts holding the frame together
Remove motor shaft from bearings
Put a drop of STP into the rear bearing
Slather a ring of STP around the front bearing
Deliberately misalign the self-aligning bearings to redistribute the slack
Reassemble in reverse order
It’s been running silently for a day, which suggests it’ll be good for quite a while…
I finally broke down and bought a Kindle Fire last week, with the intent of having my accumulation of datasheets and manuals where I need them when I need them, and it works reasonably well. One ergonomic blunder: the power button stands just slightly proud of the edge:
Kindle Fire Power Button
That’s exactly where my little finger rests when I’m supporting the slab in my left hand. Past experience has also shown that any opening will admit dust that eventually accumulates behind the screen, so a small protector seemed in order:
Kindle Power Button Protector – solid model
Printed with zero added shells and 1.0 infill produced a solid block of plastic that required very little cleanup:
Kindle power button protector – as built
The zittage serves to improve the fit: the protector should require a bit of fingernail persuasion to remove.
It took two tries to get the Micro-B USB connector slab offset from the centerline just right, but eventually everything lined up correctly:
Kindle power button protector – in place
My pudgy finger squeezes into that opening just enough to turn the thing on and off, but pressing on the green plastic bar has no effect. There’s not enough plastic to allow chamfering the edge in the solid model, but a bit of riffler file action worked wonders on those sharp edges.
The OpenSCAD source code:
// Kindle Fire Power Button Protector
// Ed Nisley KE4ZNU April 2012
include </home/ed/Thing-O-Matic/lib/MCAD/boxes.scad>
//- Extrusion parameters must match reality!
// Print with +0 shells and 3 solid layers
ThreadThick = 0.25;
ThreadWidth = 2.0 * ThreadThick;
HoleWindage = 0.2;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
Protrusion = 0.1; // make holes end cleanly
//----------------------
//- Dimensions
PlugDia = 3.5; // audio jack
PlugLength = 5.0;
PlugOffset = -10;
USBThick = 1.0; // Micro-B USB jack
USBWidth = 6.8;
USBLength = 4.0;
USBOffset = -0.25;
ButtonDia = 5.2; // power button
ButtonOffset = 10.0;
PlateWidth = 7.5;
PlateLength = 30.0;
PlateThick = 1.0;
PlateRadius = 2.0;
//----------------------
// 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,
$fn=Sides);
}
module ShowPegGrid(Space = 10.0,Size = 1.0) {
Range = floor(50 / Space);
for (x=[-Range:Range])
for (y=[-Range:Range])
translate([x*Space,y*Space,Size/2])
%cube(Size,center=true);
}
//-------------------
// Component parts
//-------------------
// Build things...
ShowPegGrid();
union() {
translate([PlugOffset,0,0])
cylinder(r=PlugDia/2,h=(PlugLength + PlateThick),$fn=8);
translate([0,USBOffset,(PlateThick + USBLength)/2])
cube([USBWidth,USBThick,(PlateThick + USBLength)],center=true);
difference() {
translate([0,0,PlateThick/2])
roundedBox([PlateLength,PlateWidth,PlateThick],PlateRadius,true,$fn=4*4);
translate([ButtonOffset,0,-Protrusion])
rotate(360/(2*8))
PolyCyl(ButtonDia,(PlateThick + 2*Protrusion));
}
}
I’ve always liked flip-top toothpaste tube caps, which Colgate tubes have and Crest tubes don’t. I’m sure there’s a reason why they use different threads; perhaps there’s a standard for toothpaste tube threads that encompasses both?
Anyhow, after years of pondering this dilemma, I jammed a Colgate cap and the top of a Crest tube onto a length of 5/16″ drill rod and eased some epoxy into the joint:
Colgate-Crest adapter – gluing
It turns out that the minor diameter of the Colgate cap is just slightly smaller than the major diameter of the Crest tube, so they don’t quite slide together. The epoxy makes for a perfect, zero-clearance fit that’s so tight you must crunch the tube to unscrew it:
Colgate-Crest adapter – thread form
For what it’s worth, that buttress thread form provides a leakproof seal in the original tube.
I have no idea whether this will actually work, because the closet has a three-pack of Colgate that should last for quite a while. Yes, we tend to buy whatever toothpaste seems cheapest on a per unit basis when we’re restocking the closet…
Unlike the previous kludge, this GPS interface case resembles an extrusion with the PCBs sliding into place, held by setscrews along the edges of the slots:
HT-GPS Adapter Case – end view
Those errant threads seem to arise from not quite bonding to the corner. The battery side of the case (bottom in this view) is one thread wide, which isn’t quite enough. Adding another thread makes it 1 mm wide, which seems excessive.
The idea was to glue the battery interface plate on that side, but printing the case vertically puts various flaws along that surface:
HT-GPS Adapter Case – bottom view
So the next iteration will merge the battery plate with the case and print the whole affair in one shot. This view shows all the parts separately:
HT-GPS Adapter Case – exploded bottom view
This shows the case joined with the battery plate, neatly aligned for printing:
HT-GPS Adapter Case – combined battery interface
The battery plate has a 0.1 mm extension into the case to avoid problems from objects with coincident planes. Unfortunately, however, that means the intersection between the base plate and the shell forms a line with three planes extending from it: the two outside walls (which are co-planar) and the plate extension inside the case. Skeinforge sometimes complains mightily about that, despite my having applied a union() to fuse the plate with the case: obviously I don’t quite understand how union() works.
I think the battery contact holes will come out close enough to being right; they all have points on the top edge to reduce the overhang problem.
One gotcha: the actual metallic contact studs for the battery. The contacts for the ICOM IC-Z1A case came from carefully shaped brass screws secured by nuts above the PCB and that’s what I’ve been designing around for this case. Unfortunately, the PCB must slide in before installing the studs, which means reaching into the depths of the case, with all the wiring in the way, to turn those nuts. Fortunately, the PCB has plenty of clearance in that direction, but … it’ll be awkward at best.
The studs also need a slot / socket / dingus to prevent rotation while tightening the nuts; right now the contact plate is circular-ish, but maybe I should rethink that.
The Wouxun KG-UV3D radio has two lugs inside the battery compartment:
Wouxun KG-UV3D – battery lugs
The battery packs and DC adapters all have clever spring-steel latches that engage those lugs, with a pair of sliding buttons that depress the ends of the spring to release the pack:
Wouxun KG-UV3D – battery pack latch
That mechanism may be cheap, straightforward, and easy to build in mass production, but I can’t figure out how to duplicate it for a case to house the GPS+Voice interface circuitry. That box had the dual disadvantages of being plug-ugly and not locking to the radio, but it did help establish some key dimensions, which is not to be sniffed at.
A bit of heads-down effort produced this not-so-hideous printable case:
HT-GPS Adapter Case – Overview
The rectangle on the top is a built-in support structure for what will be a window over the four LEDs on the Byonics TinyTrak3+ board. The two holes on the top allow screwdriver access to the TT3 trimpots, although they might not be necessary. The four holes (two visible) along the sides fit 4-40 setscrews that lock the PCBs into slots along the inside of the main case body. The red doodad off to the far side is that plug alignment block for the radio.
The yellow latch plate on the end engages the lugs with a bar sliding in a slot, which looks like this when it’s locked:
HT-GPS Case Latch – locked
A view from the top side shows the notches that release the lugs:
HT-GPS Case Latch – detail
In the unlocked position the notches and lug slots line up:
HT-GPS Case Latch – open
The solid model shows the plastic structure, which is slightly improved from the pictures:
HT-GPS Case – latch and connector plate
The big hole fits around the TinyTrak3+ serial connector to the GPS receiver. The slot across the hole splits the plate so it can fit around the already-soldered connector.
The latch bar consists of a L-shaped brass angle (from the Big Bag o’ Cutoffs) with two snippets of square brass tube soldered to the ends:
HT-GPS Case Latch – bar detail
I cut the angle to length with a Dremel abrasive wheel, soldered two brass tubes, sliced them off with a Dremel cutoff saw, roughed out the slots with the abrasive wheel, and applied some tool-and-die maker’s (aka needle) files to smooth things out. Yup, had to clamp each soldered joint in a toolmaker’s vise to keep from melting it during the nastier parts of that process. A pair of 2-56 screws, with nuts behind the plate, hold the bar in place and provide some friction.
Moving the latch bar requires poking the end with a sharp object (captured by the brass tubing), because I couldn’t figure out how to put finger-friendly buttons on it. This would be completely unusable for an actual battery, but should work OK for a permanently mounted GPS interface.
Conspicuous by their absence:
Holes in the case for the cables (may need more surface area on the ends)
Any way to fasten the latch plate to the main case (I may just drill holes for small pins)
Provision for the TT3 mode switch
A cover for the exposed radio chassis above the latch lugs (may be a separate shell glued to the latch plate)
The whole thing needs a full-up test to verify the serial connector clears the back of the case…
The Smell of Molten Projects in the Morning 