Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The ↓ (“down”) button on one of our lift chairs stopped working, although the ↑ (“up”) button worked fine and, as you’d expect, verifying this problem left the chair in a rather awkward position.
The usual power cycle and unplugging / replugging the control had no effect.
This control is the one I couldn’t pry apart to dim its LEDs, so I tried various combinations of pins until this scribble emerged:
Pride Lift Chair – control pinout doodle
I have no idea of the correct pin numbering, but the scribble looks into the connector pins with the keyway on top:
Pride lift chair control
The more intricate control for the other Pride lift chair has only four pins in its connector, so I couldn’t just swap them to see what happened.
The polarities are for the continuity / resistance test probes.
The takeaway: The two buttons did similar things to two different connector pins, so the control seemed to be working correctly and the fault lies elsewhere.
The control sports a USB jack for powering / charging your favorite device and I’m reasonably sure the control has a microcontroller tucked in there for good reason, implying the circuitry is surely more complex than maybe a rectifier bridge and some resistors.
So I shoved the chair into the middle of the room, deployed some test equipment, reconnected the control, plugged the chair power supply into the outlet strip, and … of course both buttons worked perfectly.
Soooo the chair is back in place and we’ll see what happens next.
Speaking of Heisenbugs, the HQ Sixteen continues to work fine, too.
After running reliably for a few weeks, the HQ Sixteen Heisenbug returned, displaying a Motor Stall error on the first attempt to run the motor. This gave me the opportunity to extract the PCB, compare it with the first rough schematic, then correct a few resistor values and connections.
Do not assume any connections or components are correct or correctly drawn.
!!CAUTION!! The motor supply is direct-from-the-AC-line non-isolated +160 VDC.
!!CAUTION!! The GND traces are not isolated from the AC line and are not at the normal “0 V” AC neutral potential.
When the machine operates normally, the relay pulls in with a distinct click slightly after the power switch closed. With the Heisenbug in full effect, the relay does not click, suggesting a fault in its driver circuitry.
With the motor pod resting on a box beside the machine, I gingerly measured the voltage at various points on the top of the PCB. As far as I could tell, the entire +15 VDC power supply was dead: no voltage at either the input or output terminal of the LM7815 regulator!
NOTE: The obvious screws along the top edge of the PCB are not connected to the power PCB circuit GND. Instead, they’re part of the controller’s power circuitry from the isolated power supply produced by rectifier bridge B3 and passed through J1 in the upper left corner of the PCB. Instead, the left lead on R1 (the 5W sandbox resistor) is a convenient GND terminal.
So I hauled the little DSO150 battery-powered oscilloscope and a handful of clip leads up from the Basement Laboratory, got everything arranged, turned on the power, and the machine worked perfectly again.
That’s why it’s called a Heisenbug: look at it and it vanishes.
Given a faint indication of power supply problems, I verified all four diodes in Bridge Rectifier B21 are OK and the Skynet transformer windings were solid. I resoldered all the PCB connections from the transformer to U2, the LM7815 regulator, plus the green jumper wires.
The machine is now back together, it continues to work, and all my test equipment is back in the basement.
If it happens again, I’ll mount a cheerful LED on the pod to show the supply is working.
With the manual laser pulse button in place, I measured the beam power at the entry and exit planes of Mirror 1 and Mirror 2, with the differences indicating something about the reflectivity (or lack thereof) of the molybdenum mirrors. Given that the losses are on the order of a few percent, tops, I expected this to be below the repeatability of the measurements.
The Mirror 1 entry point is basically the same as the laser tube exit:
HLP-200B – Laser tube exit
The Mirror 1 exit plane is perpendicular to that, just behind the mirror, but there is no way I can get a picture of the arrangement. Suffice it to say I do not want to ever put any body parts that close to an operating laser tube again.
The HLP-200B meter turned out to be exactly the right length to stand on its own in front of Mirror 2, although I needed a few test shots to figure out the lateral positioning:
HLP-200B Mirror 2 entry check
The Mirror 2 exit measurements were hand-held, with the meter braced against the mirror mount brackets on the gantry:
HLP-200B Mirror 2 exit
Without further ado, the results:
M1 Entry
M1 Exit
M2 Entry
M2 Exit
35.5
31.2
30.3
32.9
28.3
30.6
29.1
32.6
31.8
22.8
27.8
28.9
30.3
29.0
29.4
28.5
26.9
28.4
28.7
27.0
31.1
31.7
28.6
26.9
30.7
29.0
29.0
29.5
2.99
3.27
0.84
2.67
The bold line gives the average of the six measurements at each position, with the sample standard deviation below that.
As expected, the pulse-to-pulse variations swamp any actual differences between the entry and exit power levels; Mirror 2 does not have a net power gain. A 2% loss in the mirror is 0.6 W at 30 W, obviously far too small for the HLP-200B meter to resolve.
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.
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 Statusor 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:
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:
Optoisolator case
A strip of good foam tape sticks it to the controller:
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:
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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 hFE 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 VCE is held at 5 V) seemed reasonable. In actual use, VCE 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.
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
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
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
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
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.
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The Smell of Molten Projects in the Morning 
