LitUp LED Light Pad: Direct Wiring

Unfortunately, reinforcing the USB Micro-B jack on the side of the LitUp LED Light Pad only delayed the inevitable: the light became erratic even without the slightest touch. The pad consists of three acrylic sheets glued together around the entire perimeter, so there’s no way to get access to the no-user-serviceable-parts within. Apparently, you’re supposed to just throw it out.

On the other paw, it’s already dead, so there’s nothing to lose:

LitUp LED Light Pad - failed USB jack
LitUp LED Light Pad – failed USB jack

A little deft razor knife work chopped through the rear sheet without doing any (more) damage to the PCB within. The LEDs can still be convinced to light, but the USB jack is definitely wrecked.

Applying some ChipQuik let me extract the jack without (too much) more damage. Rather than replace it, I just soldered a pigtail USB cable to the obvious PCB pads:

LitUp LED Light Pad - direct power wiring
LitUp LED Light Pad – direct power wiring

If I’d noticed that little solder ball, I’d have removed it before filling the cavity with hot melt glue and squishing the cut-out piece of white acrylic in place.

A little black duct tape should keep the wiring stable enough for the foreseeable future:

LitUp LED Light Pad - redirected cable
LitUp LED Light Pad – redirected cable

That was another (relatively) easy zero-dollar repair that should not be necessary.

70 inch OD Curved Quilting Layout Template

Mary sketched a quilt layout on ordinary Letter-size paper using her quilting templates, but the final design will be a 30×30 inch layout requiring a suitably upscaled template. Running the numbers suggested a template with curved edges lying on a 70 inch diameter circle, which was easy enough:

Quilting Template - 70 inch dia - short
Quilting Template – 70 inch dia – short

The normal-size acrylic template with a 20 inch diameter sits atop the upscaled cardboard version. We decided cardboard would work fine for a single-use tool; should she need one in the future, I have the technology.

It turns out that the inner curve also has a 70 inch diameter: its center point is displaced 200 mm along the center radius from the outer curve. The straight sides are parallel, not radii of either circle.

She decided a much longer template would simplify smooth edge-to-edge curves, so I laid out a skinnier version with a keyed joint in the middle:

Quilting Template - 70 inch dia - long
Quilting Template – 70 inch dia – long

The grid represents the OMTech laser’s 700×500 mm platform, so I used LightBurn’s Cut Shapes function to chop the template into two overlapping parts:

Quilting Template - 70 inch dia - split
Quilting Template – 70 inch dia – split

The cuts at the keyed ends extend slightly more than needed, but weren’t critical. Similarly, I didn’t worry about kerf compensation for two pieces of cardboard joined by packing tape.

The template looks a lot like a scimitar:

Quilting Template - 70 inch dia - long
Quilting Template – 70 inch dia – long

The shorter version had its corrugations running along the short dimension. I put the longer version’s corrugations along the longer dimension, thinking they would prevent bending. That was true, but they also interfered with the pencil tracing the curves. Next time, I’ll know better!

Paracord Hot Knife

An upcoming project calls for cutting dozens of lengths from a spool of 550 (pound tensile strength) all-nylon paracord, which means I must also heat-seal the ends. Cold-cutting paracord always produces wildly fraying ends, so I got primal on an old soldering iron tip:

Paracord cutting - flattened soldering iron tip
Paracord cutting – flattened soldering iron tip

Bashed into a flattish blade, it does a Good Enough job of hot-cutting paracord and sealing the end in one operation:

Paracord cutting - results
Paracord cutting – results

Setting the iron to 425 °C = 800 °F quickly produces reasonably clean and thoroughly sealed cut ends.

Obviously, I need more practice.

Yes, I tried laser cutting the paracord. Yes, it works great, makes a perfectly flat cut, and heat-seals both ends, but it also makes no sense whatsoever without a fixture holding a dozen or so premeasured lengths in a straight line. No, I’m not doing that.

B4-size Light Pad: Stabilizing the USB Connector

What used to be a “light box” had become a “light pad” powered through a USB Micro-B connector on the side. Unfortunately, the pad’s 5 mm thickness allows for very little mechanical reinforcement around the USB jack, while providing infinite opportunity to apply bending force. Over the course of the last half-dozen years (during which the price has dropped dramatically, despite recent events), the slightest motion flickered the LEDs.

So I squished the jack’s metal shell back into shape, found a short right-angle USB cable, and conjured a reinforcing fixture from the vasty digital deep:

LitUp LED Light Pad
LitUp LED Light Pad

The plate fits under the light pad, where a strip of super-sticky duct tape holds it in place:

LitUp Light Pad USB jack reinforcement - bottom
LitUp Light Pad USB jack reinforcement – bottom

The USB plug fits between the two blocks with hot-melt glue holding it in place and filling the gap between the plug and the pad.

I’d like to say it’s more elegant than the cable redirection for my tablet, but anything involving black electrical tape and hot-melt glue just isn’t in the running for elegant:

LitUp Light Pad USB jack reinforcement - top
LitUp Light Pad USB jack reinforcement – top

On the other paw, that socket ought to last pretty nearly forever, which counts for a whole lot more around here.

The retina-burn orange tape patches on the connector eliminate all the fumbling inherent to an asymmetric connector with invisible surface features. The USB wall wart on the other end of the cable sports similar markings.

The OpenSCAD source code as a GitHub Gist:

// Bracket to protect USB jack on LitUp LED Pad
// Ed Nisley KE4ZNU 2022-03-28
Protrusion = 0.1; // make holes end cleanly
Pad = [10.0,30.0,1.2];
Plug = [8.0,10.5 + 0.5,8.0];
BasePlate = [Pad.x + Plug.x,Pad.y,Pad.z];
//----------
// Create parts
module Stiffener() {
difference() {
union() {
translate([-Pad.x,-BasePlate.y/2,0])
cube(BasePlate,center=false);
translate([0,-Pad.y/2,0])
cube([Plug.x,Pad.y,Plug.z],center=false);
}
translate([-Protrusion,-Plug.y/2,-Protrusion])
cube(Plug + [2*Protrusion,0,Plug.z],center=false);
}
}
//----------
// Build them
Stiffener();

Gidget II Sewing Table: Temporary Juki Insert

Mary’s new sewing table just arrived, but the laser-cut acrylic insert fitting around her Juki sewing machine is still a month or two away. Until then, a simple cardboard replacement must suffice to fill the gap:

Juki temporary table insert
Juki temporary table insert

The rectangle just to the left of the needle is a hatch for bobbin changes. Sheer faith and an interference fit between layers of Kapton tape holds it in place with surprising force.

I wanted to tape the cardboard edges to the machine and the table to smooth out the transitions, but her Supreme Slider slippery sheet may solve the problem without adhesives:

Juki temporary table insert - Super Slider
Juki temporary table insert – Super Slider

The “insert” is a 1/4 inch thick double-layer corrugated cardboard sheet, utility-knifed from a huge box. She layers cardboard under the wood chips in her Vassar Farms garden paths to discourage the weeds; this seemed like a perfectly reasonable diversion.

Juki JC-001 Foot Control: Resolving Uncommanded Thread Cutting

Mary’s most recent quilt arranges her color choices in Judy Niemeyer’s Stellar Snowflake pattern:

Stellar Snowflake Quilt - in progress
Stellar Snowflake Quilt – in progress

Her Juki TL-2010Q sewing machine has a built-in thread cutter activated by pressing down on the heel end (to the left) of the foot control:

Juki JC-001 Foot Control - overview
Juki JC-001 Foot Control – overview

The machine had previously performed “uncommanded” thread cuts on other projects, but the many short segments in this pattern triggered far too many cuts. I aimed a camera at her foot on the pedal and she was definitely not pressing down with her heel when the cutter fired.

In point of fact, the thread cutter fired when she was just starting a new segment, where she was gently pressing down on the toe end (to the right) of the pedal to start at the slowest possible speed.

For completeness, the underside of the pedal:

Juki JC-001 Foot Control - bottom
Juki JC-001 Foot Control – bottom

There are no screws holding it together. The top cover pivots on a pair of plastic pegs sticking out from the base near the middle of the cable spool. Disassembly requires jamming a pair of husky Prydrivers in there and applying enough brute force to pry both sides outward farther than you (well, I) think they should bend. This will scar the bottom of the case, but nobody will ever notice.

The foot control cable plugs into the machine through what looks like an ordinary two-conductor coax plug, just like the ones on wall warts delivering power to gadgets around the house. In this day and age, the communications protocol could be anything from a simple resistor to a full-frontal 1-Wire encrypted data exchange.

Based on the old Kenmore foot pedals, I expected a resistive control and, indeed, a simple test gave these results:

  • Idle = 140 kΩ
  • Heel pressed (cut) = 46 kΩ
  • Toe slight press (slow running) = 20 kΩ
  • Toe full press (fast running) = 0.2 kΩ

We can all see where this is going, but just to be sure I pried the top off the control to reveal the insides:

Juki JJC-001 Foot Control - interior
Juki JJC-001 Foot Control – interior

The two cylindrical features capture the ends of a pair of stiff compression springs pressing the top of the pedal upward.

The small, slightly stretched, extension spring in the middle pulls the slider to the left (heelward), with a ramp in the top cover forcing it to the right (toeward) as the speed increases.

The top cover includes a surprisingly large hunk of metal which may provide enough mass to make the pedal feel good:

Juki JC-001 Foot Control - top underside
Juki JC-001 Foot Control – top underside

The ramp is plastic and the slider has a pair of nylon (-ish) rollers, so there’s not much friction involved in the speed control part of motion. Yes, this is oriented the other way, with the heel end over on the right.

The metal insert pivots in the serrated plastic section near the middle, with the two husky extension springs visible on the left holding it against the plastic cover. The two rectangular features on the left rest under the plastic flanges on the right of the base to prevent the metal insert from moving upward, so pressing the heel end down pulls the cover away from the insert to let the slider rollers move toward the right end of the ramp, into roughly the position shown in the interior view.

A closeup look at the slider shows the rollers and the PCB holding all of the active ingredients:

Juki JC-001 Foot Control - Resistor Slider
Juki JC-001 Foot Control – Resistor Slider

I think the trimpot adjusts the starting resistance for the slider’s speed control travel. It is, comfortingly, roughly in the middle of its range.

A top view shows the fixed 140 kΩ resistor (brown yellow black orange, reading from the right) setting the idle resistance:

Juki JC-001 Foot Control - PCB top view
Juki JC-001 Foot Control – PCB top view

Measuring the resistance while gently teasing the slider showed that it’s possible to produce a resistance higher than 20 kΩ and lower than 140 kΩ, although it requires an exceedingly finicky touch and is completely unstable.

Before looking inside the pedal, we thought the cutter was triggered by an actual switch closure with the heel end most of the way downward against those stiff springs, which meant the failure came from a switch glitch. Now, we think the earlier and infrequent uncommanded thread cuts trained Mary to start very carefully to be very sure she wasn’t glitching the cutter’s hypothetical switch. Of course, her gradually increasing toe pressure moved the slider very slowly through its idle-to-running transition: she was optimizing her behavior to produce exactly the resistance required to trigger the cutter.

She now sets the machine’s speed control midway between Turtle and Hare to limit its top speed, presses the pedal with more confidence to minimize the time spent passing through the danger zone, and has had far few uncommanded thread cuts. We think it’s now a matter of retraining her foot to stomp with conviction; there’s no hardware or software fix.

I’m sure Juki had a good reason to select the resistances they did, but I would have gone for a non-zero minimum resistance at the fast end of travel and a zero-resistance switch to trigger the cutter.