Tag: Improvements

Making the world a better place, one piece at a time

Stack Light: Controller Wiring
A stack light above the laser cutter makes the controller’s input and output status easily visible:

Stack Light – all on

Which will be especially valuable while I’m bypassing safety interlocks and poking around inside the cabinet.

The light is unavoidably upside-down from the industrial standard, because I ~~can’t~~ don’t want to mount it on the laser cabinet, and my use of color does not match the industrial convention. Neither of which matter for my simple needs.

In order from top to bottom:
- White = high flow assist air turned on
- Blue = chiller running, water flow / temperature good
- Green = controller running a job
- Orange = lid down
- Red = laser beam active
The blue and orange lights turn on when their inputs are active, so they positively show sensor satisfaction, rather than laser-disabling dissatisfaction. The entire stack lights up while the controller runs a job with assist air turned on, which is usually the case.

(See below for a slipstream update.)

The wiring diagram on the case is the only documentation enclosed with the stack light:

Stack Light – label diagram

Any power supply between 12 VDC and 24 VDC will work and, contrary to the label, the COM lead can be either polarity: the light works in either common-anode or common-cathode configuration. Because the laser controller inputs and outputs are all low-active, I wired the COM terminal to +24 V, so pulling the other leads to GND turns on their lights.

The overall connection diagram, in order from easy to hard:

Stack Light – wiring diagram

Some of the details behind the diagram explain what’s going on.

Stack Light – water protect wiring diagram

The water flow sensor is wired in series with the chiller, with a GND connection on the far end pulling the WP controller terminal low when both sensors are happy; the switches can handle another 50 mA of LED current with no problem.

Stack Light – L-ON wiring diagram

The HV power supply has an internal pullup to +5 V on its L terminal, which means the L-ON output terminal sits at +5 V when the laser tube is off. Connecting the stack light directly to the L-ON terminal dumps the LED current into the 5 V supply through the pullup resistor, producing a somewhat weak glow in the LED when it should be off.

Running the optoisolator input from 5 V solves that problem, as its diode will be off when the L-ON output is high. When it’s low, the diode turns on, the isolator’s output transistors conduct, and the stack light gets the full 24 V it expects.

Stack Light – lid sensor wiring diagram

The lid sensor normally goes only to the IntLock controller terminal, but I also ran it to the otherwise unused P terminal on the HV power supply, in the possibly misguided belief it would prevent the supply from firing with the lid up if it failed like the first one. Those two inputs have 5 V pullups, so the optoisolator handles the stack light’s 24 V supply.

Stack Light – status and assist air wiring diagram

When I added the dual-path air assist plumbing, diode D1 turned on the air pump when either the Status or the AuxAir output turned on. When the job calls for assist air, the AuxAir output opens a valve to increase the air flow.

The Status output is active when the controller is running a job and that’s generally the only time the AuxAir output will be active, but the machine console has an Air button that manually activates it, so diode D2 isolates the Status output in that unusual situation.

Slipstream update: I realized swapping the green & orange lights would make more sense:
- White = high flow assist air turned on
- Blue = chiller running, water flow / temperature good
- Green = lid down
- Orange = controller running a job
- Red = laser beam active
Done!
2025-01-15

Stack Light: EL817 Optoisolator Case

Rather than let the boosted optoisolators flop around:

Stack Light - controller hairball wiring — Stack Light – controller hairball wiring

A small case seemed like a Good Idea™:

Optoisolator Case - OpenSCAD — Optoisolator Case – OpenSCAD

The little hex standoffs have M3 threads, although 6 mm screws are about as much as they’ll take. The recesses have clearance for the boost transistor underneath the PCB, but it’s your responsibility to not let random wires get in trouble with the exposed circuitry:

A strip of good foam tape sticks it to the controller:

Stack Light - controller wiring — Stack Light – controller wiring

Admittedly, the stack light wiring remains something of a hairball, but it’s in a good cause.

The OpenSCAD code can build as many cavities as you need:

Optoisolator Case - x5 - OpenSCAD — Optoisolator Case – x5 – OpenSCAD

The OpenSCAD source code as a GitHub Gist:

	// Optoisolator case
	// Ed Nisley – KE4ZNU
	// 2025-01-09

	include <BOSL2/std.scad>
	include <BOSL2/threading.scad>

	// Number of isolator mounts
	NumMounts = 2;

	/* [Hidden] */

	Protrusion = 0.1;

	PCB = [40.5,15.5,1.6]; // optoisolator PCB

	LipWidth = 0.8; // support lip under PCB

	Margin = [8.0,3.0,4.5]; // clearance around PCB

	BaseThick = 3.0; // underneath

	Block = PCB + [2Margin.x, 2Margin.y, (Margin.z + BaseThick)];
	echo(Block = Block);

	HolesOC = [9.5,10.0]; // M3 mounting holes (upper left / lower right)

	$fn = 3*4;

	//———-
	// Construct one mount

	module Mount() {

	union() {
	difference() {
	cube(Block,anchor=BOTTOM);

	up(Block.z – PCB.z)
	cube(PCB + [0,0,Protrusion],anchor=BOTTOM);

	up(BaseThick)
	cube(PCB – 2*[LipWidth,LipWidth,0] + [0,0,Block.z],anchor=BOTTOM);
	}

	for (i=[-1,1])
	translate([iHolesOC.x/2,-iHolesOC.y/2,BaseThick])
	threaded_nut(5.0,3.1,Margin.z,0.5, // flat size, root dia, height, pitch
	bevel=false,ibevel=false,anchor=BOTTOM);

	}

	}


	//———-
	// Mash together as many mounts as needed

	union()
	for (j=[0:(NumMounts – 1)])
	back(j*(Block.y – Margin.y))
	Mount();

view raw Optoisolator Case.scad hosted with ❤ by GitHub

2025-01-14

Stack Light: Optoisolator Boost Transistor
The LEDs in each stack light layer require a current sink handling about 50 mA, far above the ability of cheap optoisolators based on the EL817 photocoupler:

Optoisolator – OEM schematic

I’ll go into the motivation for optocouplers along with the laser controller wiring details.

As delivered, the PCB has:
- R1 = 1 kΩ (a convenient 1 V/mA current sense)
- R2 = 10 kΩ (a rather high-value pullup)
The idea is to add an able-bodied transistor to the output in a Darlington configuration:

Optoisolator – Darlington output

Some rummaging produced a small bag of 2N3904 transistors, although nearly any small NPN transistor will suffice. Removing R2 cleared the field for modification:

Optoisolator modification – top

The 2N3904 transistor (with the usual EBC pinout) fits face-down under the PCB:

Stack Light – optoisolator transistor

The cross-legged layout conceals the emitter and base leads being soldered snugly to the former OUT and GND terminals, respectively, with the collector going to the VCC terminal. The terminals thus become:
- VCC → Collector
- OUT → Emitter
- GND→ X (no connection)
Although I have little reason to believe the EL817 chips are anything other than what they claim to be, their topmarks seemed rather casual:

EL817 optocoupler – top view

The other four chips carried C333 rank + date codes.

The datasheet says the C means the Current Transfer Ratio is 200% to 400%: the output current should be 2× to 4× the diode current. The test condition are 5 mA into the diode and 5 V across the transistor terminals. A quick test:
- 2 mA → 4 mA = 2×
- 5 mA → 15 mA = 3×
- 10 mA → 35 mA = 3.5×
- 12 mA → 40 mA = 3.3×
The output transistor is rated only to 50 mA, so I stopped at 40 mA. The CTR is between 200% and 350% over that range, suggesting the parts are really real.

The 2N3904 should have an h_FE above 60 in that current range and multiply the EL817 gain by about that amount. Another quick test in the Darlington configuration, now with the 5 V supply across the 2N3904:
- 100 µA → 8.1 mA = 81×
- 250 µA → 43 mA = 172×
- 500 µA → 83 mA = 166×
The overall current gain is 40× to 50×, less than the estimate, but plenty high enough for my purposes. If you cared deeply, you’d run a circuit simulation to see what’s going on.

Knowing I needed only 50-ish mA, stopping with the transistor burning half a watt (because V_CE is held at 5 V) seemed reasonable. In actual use, V_CE will be on the order of 1 V and the dissipation will be under 100 mW.

A quick test shows they work as intended:

Stack Light – controller hairball wiring

But, yeah, talk about hairballs. Those things cry for little housings to keep them out of trouble.

The chonky lumps with orange stripes are Wago Lever-Nut connectors: highly recommended.
2025-01-13

Stack Light Base

Having external indications for the laser cutter’s internal status signals seemed like a good idea and, rather than build the whole thing, I got a five-layer stack light:

Stack Light - disassembly — Stack Light – disassembly

It arrives sans instructions, apart from the data plate / wiring diagram label on the housing, so the first puzzle involves taking it apart to see what’s inside. My motivation came from a tiny chip of blue plastic on the kitchen table where I’d opened the unpadded bag. Apparently, a mighty force had whacked the equally unpadded box with enough force to crack the blue lens, but I have no idea how the sliver escaped the still-assembled stack.

Anyhow, hold the blue/green lenses in one hand and twist the red/yellow lenses counterclockwise as seen looking at the cap over the red layer. Apply more force than you think appropriate and the latches will reluctantly give way. Do the same to adjacent layers all the way down, then glue the blue chip in place while contemplating other matters.

A switch on each layer selects either steady (the default and what I wanted) or blinking (too exciting for my needs). Reassemble in reverse order.

A Stack Light generally mounts on a production-line machine which might have a suitable cutout for exactly that purpose. I have no such machine and entirely too much clutter for a lamp, so I screwed it to a floor joist over the laser:

Stack Light - installed — Stack Light – installed

The tidy blue PETG-CF base started as a scan of the lamp’s base to serve as a dimension reference:

Stack Light - base scan — Stack Light – base scan

Import into LightBurn:

Draw a 70 mm square centered on the workspace
Round the corners until they match the 13 mm radius
Draw one 5.6 mm circle at the origin
Move the circle 52/2 mm left-and-down
Turn it into a 4 element array on 52 mm centers
Verify everything matches the image
Export as SVG

Import into Inkscape:

Put the perimeter on one layer
Put the four holes on another
Center around an alignment mark at a known coordinate
Save as an Inkscape SVG

Import into OpenSCAD, extrude into a solid model, and punch the holes:

Stack Light Mount base - solid model — Stack Light Mount base – solid model

The lip around the inner edge aligns the lamp base.

If I ever make another one, I’ll add pillars in the corners to put the threaded brass inserts close to the top for 10 mm screws instead of the awkward 30 mm screws in this one. More than a single screw hole in the bottom would align it on whatever you’re indicating.

Now, to wire the thing up …

The OpenSCAD source code as a GitHub Gist:

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view raw Stack Light – base layout.svg hosted with ❤ by GitHub

	// Stack Light mount
	// Ed Nisley – KE4ZNU
	// 2025-01-03

	include <BOSL2/std.scad>

	/* [Hidden] */

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

	BaseCenter = [100,100,0];

	Base = [70,70]; // nominal, for figuring holes

	Insert = [4.9,5.9,6.0];

	PlateThick = Insert[LENGTH];

	HolderTall = 24.0;

	WallThick = 2.7; // outer wall of light base

	LipThick = 1.5; // alignment lip inside light base
	LipTall = 0.75;

	CableOD = 5.0;

	Protrusion = 0.1;

	difference() {

	translate(-BaseCenter)
	linear_extrude(height=HolderTall + LipTall)
	import("Stack Light – base layout.svg",layer="Base Perimeter");

	up(Insert[LENGTH])
	translate(-BaseCenter)
	linear_extrude(height=HolderTall – LipTall)
	offset(delta=-(WallThick + LipThick))
	import("Stack Light – base layout.svg",layer="Base Perimeter");

	up(HolderTall)
	linear_extrude(height=HolderTall,convexity=5)
	translate(-BaseCenter)
	difference() {
	offset(delta=WallThick) // avoid glitches on perimeter edge
	import("Stack Light – base layout.svg",layer="Base Perimeter");
	offset(delta=-WallThick)
	import("Stack Light – base layout.svg",layer="Base Perimeter");
	}

	down(Protrusion)
	translate(-BaseCenter)
	linear_extrude(height=2*HolderTall,convexity=5)
	import("Stack Light – base layout.svg",layer="Base Holes");

	up(HolderTall/2)
	yrot(90) zrot(180/6)
	cylinder(d=CableOD,h=Base.x,$fn=6);
	}

view raw Stack Light Mount.scad hosted with ❤ by GitHub

2025-01-10

PrusaSlicer Scarf Joints

The release notes for PrusaSlicer 2.9 mention the addition of scarf joints on outer perimeters. Smooth joints seem like a Good Idea™, so I turned it on for comparison with a recent object:

Double Gear fidget toy – scarf vs normal

Those are flipped from the as-printed orientation: the orange ring builds upward, starting with two concentric threads on the platform.

The normal aligned joint is on the right above, with a closer look here:

Double Gear fidget toy – normal joInt

The scarf joint has a offset between layers:

Double Gear fidget toy – scarf joint

The PrusaSlicer visualization shows the effect, looking up from below the platform:

Double Gear fidget toy – scarf joint visualization

The blue PETG-CF parts have no visible seams anywhere with either setting, probably because the stuff swells slightly and obliterates any subtle differences.

Scarf joints don’t make much difference for a fidget toy, but should improve the outcome for more critical circular / spherical models.

2024-12-31
OMTech 60 W Laser: Manual Pulse Button

I want to put the HLP-200B Laser Power Meter at the tube’s exit, just upstream from Mirror 1, where it can measure the laser’s power output before the mirrors get into the act. Reaching the Pulse button on the machine console requires much longer arms than any normal human can deploy, plus a certain willingness to lean directly over a laser tube humming with 15 kV at one end.

Perusing the KT332N doc brings up a hint, blocked in red so you can make some sense of it:

KT332N Input bits

A few minutes with boxes.py produces a simple two-compartment box and a few minutes with LightBurn adds two holes:

Remote Switch Box – LightBurn layout

Another few minutes produces the box from Trocraft Eco, which is not quite thin enough for the switch (from my Box o’ Clicky Buttons) to snap into place, but a few dabs of hot melt glue hold it down:

Laser remote pulse button – installed

Double-sided foam tape sticks the box to the laser frame and the red-n-black cable snakes all the way across the back of the machine and through the electronics bay to the IN2 and GND terminals of the KT332N INPUT block:

Laser remote pulse button – Ruida KT332N wiring

With the laser head parked at a safe spot and all interlocks happy, it works:

Laser remote pulse button – demo

That is a re-enactment, because I lack sufficient dexterity to handle a phone with my left hand, poke the button with my right finger, and not damage anything important.

The general idea is to make it very difficult to inadvertently press that button: you must want to fire the laser with the tube compartment hatch up (it has no interlocks) and the control panel out of sight on the top-front of the machine.

Setting the power to 30% and putting the meter in harm’s way:

HLP-200B – Laser tube exit

Again, a reenactment based on actual events.

Five pulses later:

40.8 W
42.4
42.3
41.2
40.7
41.5 W avg
0.82 W std dev

For the record, those five pulses dumped about 5 × 42 W × 10 x ≅ 2000 W·s = 2 kJ into the meter, raising it from “chilly basement ambient” to “be careful where you hold it”, thus making the meter’s aluminum case the least-efficient handwarmer in existence.

The 30% PWM measurements at the center of the platform came out slightly lower: 38.5 W average with a sample standard deviation of 2.2 W.

The large standard deviations prevent firm conclusions, but, yeah, the power at the tube exit seems about right, before two mirrors and ≅800 mm of path length take their toll.

The LightBurn SVG layout as a GitHub Gist:

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view raw Remote Switch Box – LightBurn layout.svg hosted with ❤ by GitHub

2024-12-30

HLP-200B Laser Power Meter: First Measurements

The HLP-200B Laser Power Meter arrives without much in the way of specifications:

The HLP-200B Laser Power Meter Handheld comes fully calibrated at 10.6 μm (CO2). Each laser power meter we calibrate is directly traceable to NIST absolute standards because we use GOLD standards as a reference for each calibration. You will obtain the most accurate result possible

A line in the description says “+/- 3% within the central section”, but that’s not much help. Back in the day, any error percentage referred to the meter’s full-scale value, which would be ±6 W for a 200 W meter.

So I plunked the meter in the middle of the laser platform:

HLP-200B Laser Power Meter - platform center — HLP-200B Laser Power Meter – platform center

Then took five measurements at each of ten power levels:

PWM %	10	20	30	40	50	60	70	80	90	99
°C	17.2	17.9	18.4	19.0	19.4	20.3	20.0	20.0	20.5	19.4
Tube Current	3	4	7	10	14	16	18	20	22	24
W	7.1	21.0	42.0	51.8	59.1	63.0	67.8	69.6	74.7	64.0
	6.0	19.8	37.2	48.9	52.7	56.0	65.1	69.6	72.4	71.8
	6.4	21.1	39.3	45.6	56.5	53.2	61.1	60.7	74.6	75.2
	5.6	17.8	37.1	40.4	55.3	53.2	55.1	64.2	74.9	73.5
	6.0	17.7	36.9	45.1	54.5	53.1	62.2	69.9	72.2	70.9
Avg Power	6.2	19.5	38.5	46.4	55.6	55.7	62.3	66.8	73.8	71.1
std dev	0.57	1.66	2.19	4.29	2.39	4.26	4.78	4.16	1.34	4.29

That’s easier to digest from a graph:

HLP-200B Laser Power Meter - 60 W platform center measurements — HLP-200B Laser Power Meter – 60 W platform center measurements

The absurdity of computing the sample standard deviation from five measurements taken at each power level does not escape me, but this just surveys the situation.

Earlier measurements of the tube current vs. PWM setting, using an RMS value computed by the oscilloscope’s firmware, produced a plot resembling the brown points (read the mA scale on the right) at the high end and differing greatly on the low end. These values come from the power supply’s digital meter, but the straight-line fit doesn’t look absurdly forced and the zero intercept seems plausible. I *assume* it’s actually measuring the tube current, rather than displaying a value computed from the PWM input, but I don’t know for sure.

The rather sketchy paperwork accompanying the laser had one handwritten “21 mA” seemingly corresponding to 60 W output, which looks approximately correct. The instruction manual has a table of power vs. current suggesting that 65-ish W corresponds to 18 mA, with 100 W at 23 mA; it’s unclear whether that is for the 60 W tube in the machine or applies to the entire range of available tubes. The manual recommends not using more than 95% PWM, with which I heartily agree.

Because my meter stand holds the target in the same position relative to the beam during successive measurements much better than I could by hand, I think the pulse-to-pulse variation comes from meter and tube repeatability.

Earlier measurements with a grossly abused Gentec ED-200 joulemeter suggested the laser has some pulse-to-pulse timing variation, down in the millisecond range, but produced roughly the right power for middle-of-the-range PWM settings. This meter integrates the beam power over about ten seconds, so I think variations will be due to (possible) tube power changes and meter repeatability, rather than timing errors.

Obviously, you must not depend on any single-shot measurement to fall within maybe 10% or several watts of the right answer.

With all that in mind and assuming the meter is delivering approximately the right numbers on average, the power supply overcooks the tube at any PWM setting above 50%. I’ve noticed some beam instability / defocusing over 80% while cutting recalcitrant materials, which is surely due to the tube not lasing properly. I generally avoid doing that.

The log fit to the measured power looks better than I expected, although I’m unprepared to compute natural logs in my head.

Hey, it’s my idea of a good Christmas present …

2024-12-25

40.8	W
42.4
42.3
41.2
40.7
41.5	W avg
0.82	W std dev

Tag: Improvements

Stack Light: Controller Wiring

Stack Light: EL817 Optoisolator Case

Stack Light: Optoisolator Boost Transistor

Stack Light Base

PrusaSlicer Scarf Joints

OMTech 60 W Laser: Manual Pulse Button

HLP-200B Laser Power Meter: First Measurements