The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Category: Electronics Workbench

Electrical & Electronic gadgets

Craptastic Kitchen Scale Tinkering
The health plan I use pays $100 toward the year’s over-the-counter healthcare stuff, although with a caveat: you can only buy the stuff from a specific website. As you might expect, what’s available consists of no-name generic products with absurdly high sticker prices and, just to rub it in, the hundred bucks gets paid in quarterly use-it-or-lose it installments.

Seeing as how it was free, I got a kitchen scale:

SmartHeart 19-106 Kitchen Scale – top view

It has two catastrophically bad design features:
- Terrible battery life
- Overly sensitive controls
It runs from a pair of series-connected CR2032 non-rechargeable lithium coin cells. Which would be fine, except that the blue LED backlight stays on for 30 seconds after each button touch and draws about 10 mA.

The battery lifetime is best measured in days.

The four control “buttons” on either side of the backlit LCD are touchless sensors using copper foil stickers:

SmartHeart 19-106 Kitchen Scale – NP-BX1 retrofit

The alert reader will spot those the empty CR2032 coin cell contacts over on the left and a pair of NP-BX1 batteries in the middle.

I figured there was no need to keep feeding it coin cells while I played with it, so I conjured a holder from the vasty digital deep. Normally, that would be an OpenSCAD solid model suited for 3D printing, but in this case the lithium cells exactly filled the space between the PCB and the bottom of the case, so it became a 2D design neatly suited for laser cuttery.

Kitchen scale – NP-BX1 holder – LB layout

I planned to stick the orange cutout (in 1.5 mm acrylic) as a stabilizer around the pogo pins making contact with the cell terminals from the red cutout (in 3 mm acrylic), but just melting the pins into the acrylic seemed sufficient for the purpose. Strips of adhesive sheet saved from the margins of previous projects affix the holder (not the cells!) to the scale’s upper glass layer.

As far as I can tell, the scale is perfectly happy running on 7.4 V, rather than 6.0 V. The PCB has two terminals marked +3V and +6V, so it probably depends on which LEDs they use for backlights:

SmartHeart 19-106 Kitchen Scale – PCB detail

The alert reader will notice a peculiarity concerning the sensor pad connections along the top edge.

More on that second bad design decision later …
2023-03-20
Bafang Motor Connector Gasket Replacement

Reasonable people disagree as to the cause of the failure, but a replacement controller for the (new) Bafang motor I’m installing on my bike just arrived in the mail.

Disassembling the motor is straightforward, except for the part where you must excavate an internal plug from the silicone snot gluing it into place, eventually revealing its socket:

Bafang motor – interior gasket – connector

Regrettably, there seems no way to do that without destroying the dense closed-cell gasket around the connector:

Bafang motor – interior gasket – damaged original

Equally regrettable: a replacement gasket wasn’t included with the replacement controller. Although I don’t have any of the specific foam, some marginally less dense foam from the Big Box o’ Padding seemed suitable for laser cuttery:

Bafang motor – interior gasket – iterations

The upper left prototype suggested a slightly larger rear bar that produced the gasket in front, which fit snugly:

Bafang motor – interior gasket – test fit

It lacks the latch cutout, but the foam is squishy and I expect to never touch it again.

A generous glob of hot melt glue holds everything in place:

Bafang motor – interior gasket – replacement glued

Although the usual Youtube videos show folks slathering RTV silicone caulk on these connectors, that’s a Very Bad Idea™, because RTV caulk releases acetic acid as it cures. That’s not a problem in the open-air siding-and-lumber environment the caulk was intended for, but sealing a glob of the stuff inside an enclosure will eventually corrode all of the electronics therein.

Cutting intricate doodads has become trivially easy: if you can draw it, you can pretty much cut it, just like that:

Bafang motor connector gasket – LB layout

That was the easy part, anyway.

2023-03-13
ResMed ClimateLine Heated Hose Pinout

A new ResMed ClimateLine headed CPAP hose arrived on schedule and let me measure the old hose:

ResMed ClimateLine heated hose ends

The center two they-are-not-USB contacts on the input end of the hose (on the right) are for the heating element spiraling around the tube and measure 10.0 Ω.

The outer two contacts report back from what must be a 10 kΩ thermistor embedded in the dingus sticking into the hose lumen at the output end (on the left). It reads 12 kΩ in a 68 °F room and responds to warmth with a lower resistance, which is what you’d expect.

Plugging the ClimateLine hose into the AirSense 11 unit enables temperature sensing at the end of the hose, with closed loop control from 60 °F to 86 °F. Mary set it to 80 °F in manual mode, which apparently produces different results from the same temperature in Auto mode, and declared victory.

A humidity setting of 4, in the middle of the 1 – 8 range, works for her.

Both the AirSense 11 and its power brick claim 24 VDC at a suspiciously exact 2.71 A. The hose heater could soak up 2.4 A of that, but the AirSense 11 also heats the humidifier’s water tank (“tub”), so it’s unlikely they’re both seeing the full 24 V.

I am prohibited from further investigation. [grin]

2023-03-06
OMTech 60 W Laser Power Supplies
A LightBurn forum discussion about laser power supplies prompted me to finally organize my pictures.

Without looking at the captions, match each of the following pictures with its description:
- a failed ZYE MYJG60W-Y-1 (came with OMTech laser)
- an unbranded MYJG60W replacement from OMTech
- a Cloudray M60 (bought as a backup)
HV Power Supply – ZYE MYJG60W-Y-1 – failed

HV Power Supply – unbranded MYJG60W

HV Power Supply – Cloudray M60

That was easy, wasn’t it?

As I said in the forum:

My guess is there’s only one ZYE factory (or a dozen clones) producing all the power supplies, then applying whatever sticker the order calls for on the case before dropping it in the carton.

Perhaps Cloudray buys more quality control than the anonymous “brands”, but I wouldn’t lay much money on finding more than two QC bins at the end of the assembly line: either it runs or it doesn’t.
2023-02-23
Flypower Wall Wart: FAIL

The IR sensor on the under-cabinet LED lights I installed half a dozen years ago became increasingly flaky. Its wall wart power supply was on the hot side of uncomfortably warm, so I had an obvious culprit.

The data plate says it’s UL Listed, which is comforting:

Flypower LED wart – data plate

The open-circuit output of a 12 VDC power supply should not look like this:

FlyPower 12V 1A – no load

The horizontal scale is 100 ms/div, so those ramps seem much more languid than you might expect from a 60 Hz wall wart.

Adding a 16 Ω load to draw maybe 750 mA got its attention:

FlyPower 12V 1A – 16ohm load

The average may be 12 V with too-large dips at the expected 120 Hz, but looky at all the hash riding the output!

No wonder the IR sensor was having such a hard time. When the LEDs are off the voltage ramps between 16 and 5 V. When it eventually turns on the supply has impossible noise levels.

So I cracked the case and extracted the electronics:

Flypower LED wart – components

Those caps over there on the left rear don’t look healthy, do they?

Flypower LED wart – failed caps

No. No, they don’t and you shouldn’t be able to see the wiring inside the inductor between them, either.

Probing the Box o’ Wall Warts produced a similar-ish wart that only required harvesting and splicing the teeny coax plug from the failed adapter to put the LED strips back into normal operation.

The identical supply for the identical LED strips on the other side of the kitchen continues to work fine and feel only warm-ish, so I’ll let it be.

2023-02-15
RCA Alarm Clock: Recapping

A power failure apparently pushed the ancient RCA alarm clock over the edge into a mode where it ignored its pushbuttons and displayed a time based on a hitherto unknown exoplanet. Popping the case revealed it’s been simmering in its own juices for quite a while:

RCA Alarm Clock – PCB overheat

There’s nothing obviously scorched on the underside of the PCB, although a large SMD resistor might be the source of the problem.

Having been around this block a few times, I unsoldered that big electrolytic cap with its guts protruding from the overwrap:

RCA Alarm Clock – failed cap value

Nope, that’s not really an electrolytic cap any more.

Lacking a 2200 µF cap of suitable voltage rating, but knowing cap tolerances allow for considerable windage, this worked out well enough:

RCA Alarm Clock – replacement caps

Two smaller caps measuring on the low side of OK now reside in the e-waste box.

The white diffuser over the last digit improves it in ways I do not profess to understand, but am pleased to implement:

RCA Alarm Clock – in place

It’s held in place by two strips of LSE tape to see how it reacts to prolonged shear force, no matter how gentle.

2023-02-10
Kenmore 362.75581890 Oven: Another Igniter Bites The Dust
Our story so far:
- We installed a Kenmore gas range around the turn of the millennium
- 2006 – Oven burner tube & igniter replaced
- 2014 – Igniter replaced
Apparently igniters last about eight years, regardless of provenance, because the igniter just failed, with the usual symptoms of low current draw (about 2 A), failed ignition, and a faint smell of propane (well, mercaptan) before the safety valve kicked in:

Oven igniter – location

The new igniter, another low-buck Amazon offering, came with half a green plastic connector block that mated neatly with the existing half under the oven. Unfortunately, the new wires had female pins crimped on their ends, rather than the male pins required by the existing connector and the ceramic wire nuts I’d used to join the previous igniter to the OEM connector were non-removable.

So I trimmed the old wires to a usable length and applied the new ceramic wire nuts to the stubs:

Oven igniter – connector rewiring

Also as before, the new igniter measures 3 A, definitely below the low end of the valve’s 3.3 to 3.6 A range:

Oven igniter – current test

If this one lasts eight years, I won’t be the guy replacing it …
2023-01-16