Category: Electronics Workbench

Electrical & Electronic gadgets

Juki TL-2010Q: COB LED Power

The wires to my earlier LED lights on Mary’s Kenmore 158 produced one absolute requirement: the Juki TL-2010Q lights must not have any external wiring. Some experimentation showed putting the COB LED module across the rear of the arm, just over the opening, would spill enough light to the front:

Juki TL-2010Q COB LED – installed – rear view

Juki’s teeny OEM SMD LED in the endcap, just above the far side of the needle, casts a dim glow over her left hand. Although they deem it sufficient, I’ll fix that in the near future.

The machine’s power supply and drive motor live inside a plastic cover on the rear of the machine, just to the left of where the LED lights will attach to the arm:

Juki TL-2010Q COB LED – machine power supply

For future reference, a detailed look at the PCB:

Juki TL-2010Q COB LED – machine power supply PCB detail

The yellow-and-blue pair come from the AC power line switch. The brown-and-blue pair carry +120 VDC from the bridge rectifier (left of their connector) to the motor driver. The white-and-blue pair carry filtered 120 VAC from the PCB to the bulky transformer below the motor.

I snipped the white-and-blue pair, added Y connections, and threaded the wires through the vent slots to the 12 VDC power supply:

Juki TL-2010Q COB LED – 12 V supply wiring

If I had to do it again, I’d cut the white-and-blue pair an inch further away from the transformer, so as to move the butt splice connectors around the corner of the frame, rather than across the back of the transformer frame. The flanged screw boss pretty well fills the space left of the transformer and made it difficult to arrange the new connectors.

The 12 VDC 18 W LED supply attaches to the 120 VAC lines with 1/4 inch quick-disconnects, making it possible, if not easy, to completely remove the cover and LED power supply. You’d install dummy plugs in the vacant QD sockets to keep the AC out of harm’s way.

There’s just enough space to the right of the PCB enclosure to route the LED wires around-and-down to meet the wire nuts. They’re not the most elegant connectors you’ve ever seen, but wire nuts are impossible to confuse with the QD connectors on the AC line.

With that in hand, the power supply almost looks like it grew under the spool flange:

Juki TL-2010Q COB LED – 12 V supply installed

In an ideal world, the label would be right-side-up, but ya can’t have everything. The wires had to be where they are, primarily to avoid snagging on fabric passing through the machine.

The green-and-black PET braid covers the AC wires to make them a little less exposed, but it’s surely unnecessary. I gently singed the braid ends to prevent unraveling.

The COB LED supply wires emerge through a slot filed in the cover:

Juki TL-2010Q COB LED – power wires to endcap

Next step: LED brightness tweakage.

2019-02-05
Vacuum Tube LEDs: Better Radome

A two-legged ~~spider~~ radome base definitely looks better than the four-legged version:

Arduino Pro Mini – NP-BX1 – radome

The radome base now has a hole punched in its bottom for the data lead, with the two power wires going out the sides as before:

Arduino Pro Mini Battery Holder – SK6812 radome base

The alert reader will notice the vertical strut on the far side doesn’t go directly into the center of its base fitting. I attempted a bit of cosmetic repair on the horizontal wire below the Pro Mini and discovered, not at all to my surprise, (re)soldering a connection to a 14 AWG copper wire an inch away from a 3D printed base doesn’t work well at all.

Doesn’t affect the function and, as nobody will ever notice, I’ll leave it be.

2019-02-04
Epoxy Joint: Test to Destruction

Some years ago, I put the LED power supply for one of the Kenmore 158 machines atop a plastic project box with an adjustable boost supply inside:

Needle LEDs power supply – exterior

The LEDs connected through a coaxial power jack on the far side of the box, held in place with a generous blob of epoxy:

Needle LEDs power supply – interior

A closer look:

Kenmore 158 COB LED – power supply jack

I’m adding a light bar, similar to the one now going onto the Juki TL-2010Q, which needs a direct connection to the 12 VDC supply. Rather than add another coaxial jack, I ripped out the existing jack and installed a DE-9 connector (serial ports being a fading memory by now), giving me an opportunity to test the epoxy joint:

Kenmore 158 COB LED – power supply jack – epoxy bond

Which required grabbing the connector with a pair of pliers and twisting / bending / abusing until it popped free. I don’t know how much grip the scored lines added to the joint, but the connector definitely didn’t give up without a fight; it wasn’t going to fall off on its own.

To be fair, the epoxy had a better grip on the coaxial jack than on the plastic plate, perhaps because the bottom of the jack had all manner of nooks and pins intended for PCB mounting. Ya use what ya got, sez I.

The new connector looks exactly like it should and, because it’s held in place by a pair of screws, should last forever, too:

Kenmore 158 COB LED – power supply

More about all that, later …

2019-02-03
Monthly Science: Lithium Cells vs. Low Discharge Current

The amount of energy you can extract from a battery depends strongly on the discharge current, which is why the advertised capacity always exceeds the real-world capacity. Testing the NP-BX1 batteries for my Sony HDR-AS30V at about an amp produces a reasonable estimate of their run time in the camera:

Sony NP-BX1 – Wasabi GHIJK – 2017-09-01 – annotated

Even though defunct cells lack enough capacity to keep the camera alive during a typical bike ride, they should power a microcontroller or astable multivibrator for quite a while.

My CBA II has a 100 mA minimum test current, which is far higher than the 15-ish mA drawn by the Arduino Pro Mini / Nano and SK6812 LEDs in a vacuum tube light, so these tests should provide a lower bound on the expected run time:

Defunct NP-BX1 for Blinkies and Glowies – AmpHr – 2019-01

The two dotted lines show a “good” battery (Wasabi 2017 K) tested at 100 mA has a 1 A·h capacity similar to the “defunct” batteries. Testing at 1 A drops the capacity by a factor of two and eliminates the relatively constant voltage part of its discharge curve.

Handwaving: a 15 mA load on a battery with 1 A·hr capacity should run for 66 hours, ignoring nuances like the Arduino’s minimum voltage requirement and LED minimum forward voltages.

A few days of informal (“Oh, it stopped a while ago”) testing showed 50 hour run times, with little difference in the results for batteries with 800 mA·h and 1300 mA·h capacity:

Arduino Pro Mini – NP-BX1 cell – SK6812 – blue phase

The red power LED remains on long after the SK6812 LEDs dim out and the Arduino stops running. The blue and green LEDs fade before the red LED.

The run time test data:

Arduino Pro Mini – NP-BX1 run times – single SK6812 – 2019-01

The 100 mA graph plotted against watt·hours has a similar shape:

Defunct NP-BX1 for Blinkies and Glowies – 2019-01

You’d use those results for a constant power load similar to a camera or, basically, any electronics with a boost supply.

2019-02-01

Juki TL-2010Q: COB LED Light Bar

Mary needed more light under the arm of her Juki TL-2010Q sewing machine, so I proposed a 12 V 6 W COB LED module instead of the high-density LED strips I used on her Kenmore 158s:

Kenmore 158 Sewing Machine - Cool white LEDs - rear no flash — Kenmore 158 Sewing Machine – Cool white LEDs – rear no flash

Because the COB LEDs dissipate 6W, far more power than I’m comfortable dumping into a 3D printed structure, I redefined a length of aluminum shelf bracket extrusion to be a heatsink and epoxied the module’s aluminum back plate thereto:

Juki TL-2010Q COB LED - test lighting — Juki TL-2010Q COB LED – test lighting

Unlike the flexible LED strips, the COB LED modules have no internal ballast resistors and expect to run from a constant-current supply. Some preliminary testing showed we’d want less than the maximum possible light output, so a constant-voltage supply and a few ohms of ballast would suffice:

Juki TL-2010Q COB LED - ballast resistor test — Juki TL-2010Q COB LED – ballast resistor test

With all that in hand, the heatsink extrusion cried out for smooth endcaps to control the wires and prevent snagging:

TL-2010Q COB LED Light Bars - end caps - Show layout — TL-2010Q COB LED Light Bars – end caps – Show layout

The central hole in the left cap passes 24 AWG silicone wires from the power supply, with 28 AWG silicone wires snaking down through the L-shaped rectangular cutouts along the extrusion to the LED module’s solder pads.

The model includes built-in support:

TL-2010Q COB LED Light Bars - end caps - Build layout — TL-2010Q COB LED Light Bars – end caps – Build layout

Assuming the curved ends didn’t need support / anchors holding them down turned out to be completely incorrect:

Juki TL-2010Q COB LED - curled endcaps — Juki TL-2010Q COB LED – curled endcaps

Fortunately, those delicate potato chips lived to tell the tale and, after a few design iterations, everything came out right:

Juki TL-2010Q COB LED - heatsink endcap - internal connections — Juki TL-2010Q COB LED – heatsink endcap – internal connections

The “connector”, such as it is, serves to make the light bar testable / removable and the ballast resistor tweakable, without going nuts over the details. The left side is an ordinary pin header strip held in place with hot melt glue atop the obligatory Kapton tape, because the heatsink doesn’t get hot enough to bother the glue. The right side is a pair of two-pin header sockets, also intended for PCB use. The incoming power connects to one set and the ballast resistor to the other, thusly:

Juki TL-2010Q COB LED - light bar connector diagram — Juki TL-2010Q COB LED – light bar connector diagram

The diagram is flipped top-to-bottom from the picture, but you get the idea. Quick, easy, durable, and butt-ugly, I’d say.

The next step was to mount it on the sewing machine and steal some power, but that’s a story for another day.

The relevant dimensions for the aluminum extrusion:

Aluminum shelf bracket extrusion - dimensions — Aluminum shelf bracket extrusion – dimensions

The OpenSCAD source code as a GitHub Gist:

	// Juki TL-2010Q Sewing Machine – COB LED Light Bars
	// Ed Nisley – KE4ZNU
	// 2019-01

	/* [Layout Options] */

	Layout = "Build"; // [Bracket,Endcap,Show,Build]

	Wiring = [1,0]; // left and right wire holes

	BuildSupport = true;

	/* [Extrusion Parameters] */

	ThreadWidth = 0.40;
	ThreadThick = 0.20;

	HoleWindage = 0.2;

	Protrusion = 0.1;

	//—–
	// Shelf bracket used as LED heatsink

	/* [Hidden] */

	LEDPlate = [15.0,2.4]; // 2D coords from end of LED

	BktOuter = [15.9,12.6 + LEDPlate.y]; // 2D coords as seen from end of extrusion
	BktWalls = [1.3,2.2 + LEDPlate.y]; // … extend base to cover LED
	BktCap = [2.5,3.0];

	BracketPoints = [
	[0,0],
	[BktOuter.x,0],
	[BktOuter.x,BktOuter.y],
	[(BktOuter.x – BktCap.x),BktOuter.y],
	[(BktOuter.x – BktCap.x),(BktOuter.y – BktCap.y)],
	[(BktOuter.x – BktWalls.x),(BktOuter.y – BktCap.y)],
	[(BktOuter.x – BktWalls.x),BktWalls.y],
	[BktWalls.x,BktWalls.y],
	[BktWalls.x,(BktOuter.y – BktCap.y)],
	[BktCap.x,(BktOuter.y – BktCap.y)],
	[BktCap.x,BktOuter.y],
	[0,BktOuter.y],
	[0,0]
	];

	BracketPlugInsert = 10.0; // distance into bracket end

	WireOD = 1.6; // COB LED jumpers – 24 AWG silicone
	WireOC = BktOuter.x – 2*BktWalls.x – WireOD;
	echo(str("Wire OC: ",WireOC));

	CableOD = 4.0; // power entry cable

	CapSides = 234;

	//—–
	// 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);
	}

	//—–
	// Endcap with smooth rounding
	// Wires = true to punch holes for LED wires

	module Endcap(Wires = true) {

	// arc length to flatten inside of cap
	// not needed to build in normal orientation

	m = BktOuter.x/2 – sqrt(pow(BktOuter.x/2,2) – pow(BktOuter.x – 2*BktCap.x,2)/4);

	difference() {
	translate([0,0,BktOuter.y/2]) // basic endcap shape
	intersection() {
	cylinder(d=BktOuter.x,h=BktOuter.y,$fn=CapSides,center=true);
	rotate([90,0,0])
	rotate(180/CapSides)
	cylinder(d=BktOuter.y,h=BktOuter.x,$fn=CapSides,center=true);
	}

	translate([-BracketPlugInsert,0,0]) // extrusion + LED plate
	Bracket(BracketPlugInsert);

	if (false) // flatten inner end
	translate([-BktOuter.y + m,0,BktOuter.y/2])
	cube([BktOuter.y,BktOuter.x,BktOuter.y],center=true);

	if (Wires) {
	for (j=[-1,1]) // COB LED connections
	translate([WireOD – BktOuter.x/2,j*WireOC/2,(BktWalls.y + WireOD – Protrusion)/2])
	rotate([0,00,0])
	cube([BktOuter.x,WireOD + Protrusion,BktWalls.y + WireOD + Protrusion],center=true);
	translate([0,0,BktOuter.y/2]) // power entry / exit
	rotate([0,90,0])
	translate([0,0,-BktOuter.x])
	rotate(180/6)
	PolyCyl(CableOD,2*BktOuter.x,6);
	}
	}
	}

	// Totally ad-hoc support structures

	module Support(Wiring = false) {

	Spacing = 4*ThreadWidth;
	NumBars = floor((BktOuter.y/2) / Spacing);
	echo(str("Support bars: ",NumBars));

	color("Yellow") {
	render() difference() {
	union() {
	for (i=[1:NumBars]) // inside extrusion
	translate([-i*Spacing,0,(BktWalls.y + WireOD)/2])
	cube([2ThreadWidth,BktOuter.x – 0BktWalls.x,BktWalls.y + WireOD],center=true);

	if (true)
	for (j=[-1:1]) // reduce outside curve uplift
	translate([0.3BktOuter.y,jBktOuter.x/3,BktOuter.y/10])
	cube([BktOuter.y/3,2*ThreadWidth,BktOuter.y/5],center=true);
	}
	minkowski() { // all-around clearance
	Endcap(Wiring);
	cube(2.0*ThreadThick,center=true);
	}
	if (Wiring) {
	translate([0,0,BktOuter.y/2]) // remove rubble from wire bore
	rotate([0,90,0])
	translate([0,0,-BktOuter.x])
	rotate(180/6)
	PolyCyl(CableOD,2*BktOuter.x,6);
	}
	}

	if (false)
	translate([-(BktOuter.x/4 + ThreadWidth),0,ThreadThick/2]) // adhesion pad
	cube([BktOuter.x/2,BktOuter.x – BktWalls.x,ThreadThick],center=true);

	// translate([BktOuter.x/3,0,ThreadThick/2]) // adhesion pad
	// cube([0.3BktOuter.x,0.7BktOuter.x,ThreadThick],center=true);

	if (false)
	for (j = [-1:1]) // tie pad to bottom of cap
	translate([-(4ThreadWidth)/2,j(BktOuter.x – 2*ThreadWidth)/2,ThreadThick/2])
	cube([4ThreadWidth,2ThreadWidth,ThreadThick],center=true);
	}
	}

	//—–
	// Heatsink extrusion + LED plate
	// Centered on Y with Length extending in +X

	module Bracket(Length = 10)
	translate([0,-BktOuter.x/2,0])
	rotate([90,0,90])
	linear_extrude(height = Length,convexity=3)
	polygon(points=BracketPoints);

	//—–
	// Build things

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

	if (Layout == "Endcap")
	Endcap();

	if (Layout == "Show") {
	translate([BktOuter.x,0,0])
	Endcap(Wiring[1]);
	translate([-BktOuter.x,0,0])
	rotate(180)
	Endcap(Wiring[0]);
	color("Yellow",0.35)
	translate([-BktOuter.x/2,0,0])
	Bracket(BktOuter.x);
	}

	if (Layout == "Build") {
	translate([BktOuter.y,0,0]) {
	Endcap(Wiring[0]);
	if (BuildSupport)
	Support(Wiring[0]);
	}
	translate([-BktOuter.y,0,0]) {
	Endcap(Wiring[1]);
	if (BuildSupport)
	Support(Wiring[1]);
	}
	}

view raw TL-2010Q COB LED Light Bars.scad hosted with ❤ by GitHub

2019-01-31

DSO150: USB Battery Charger

Continuing the process of silk-purse-izing the DSO150, a batch of USB 1S lithium battery charger modules arrived from halfway around the planet. I drilled & filed a suitable hole / slot / aperture in one of the few remaining spots in the case, then stuck the PCB to the bottom with good foam tape:

DSO150 – USB charger – internal layout

Because the charger includes cell protection circuitry, I replaced the original protected 18650 cell with a bare cell sporting solder tabs. The cell should go directly to the charger board, but the switch disconnects the + wire; I’m unwilling to believe the charger won’t slowly and inexorably discharge the cell if I don’t use the DSO150 for a few months. It could happen.

A label makes the hole look almost professional:

DSO150 – USB charger – Micro-B jack

Well, makes it look Good Enough™, I suppose.

The power switch gets a label, too:

DSO150 – USB charger – battery switch

Flipping the switch ON lights up the scope from the battery.

The charger (sensibly) will not route power from the USB port to the scope without a battery, so you must plug in a USB source with the switch ON, then flip the switch OFF. I don’t know why you’d want to do that, but there you go.

Now it’s a real portable instrument, with all the inconvenience of managing a built-in lithium cell.

2019-01-30
Vacuum Tube LEDs: Radome Prototype

Definitely not a vacuum tube:

Arduino Pro Mini – NP-BX1 cell – SK6812 – blue phase

It’s running the same firmware, though, with the Arduino Pro Mini and the LEDs drawing power from the (mostly) defunct lithium battery.

The LED holder is identical to the Pirhana holder, with a 10 mm diameter recess punched into it for the SK6812 PCB:

Astable Multivibrator Battery Holder – Neopixel PCB – Slic3r

Those embossed legends sit in debossed rectangles for improved legibility. If I repeat it often enough, I’m sure I’ll remember which is which.

The 3.6 V (and declining) power supply may not produce as much light from the SK6812 LEDs, but it’s entirely adequate for anything other than a well-lit room. The 28 AWG silicone wires require a bit of careful dressing to emerge from the holes in the radome holder:

SK6812 LED PCB – Pirhana holder wiring

The firmware cycles through all the usual colors:

Arduino Pro Mini – NP-BX1 cell – SK6812 – orange phase

A pair of tensilized 22 AWG copper wires support the Pro Mini between the rear struts. The whole affair looks a bit heavier than I expected, though, so I should reduce the spider to a single pair of legs with a third hole in the bottom of the LED recess for the data wire.

The OpenSCAD source code needs some refactoring and tweaking, but the Pirhana LED solid model version of the battery holder should give you the general idea.

2019-01-29