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.
Electrical & Electronic gadgets
The dual switch controlling the bathroom lights began requiring some fiddling, which was not to be tolerated. After replacing the switch, I cracked the old one open to see what’s inside…
The failed side of the switch controlled the lights over the sink:
The side for the ceiling vent fan + light got much less use, still worked, and look a bit less blasted.
Not much to choose between the two. It’s been running for nigh onto two decades, so …
An RTL-SDR receiver & Ham It Up RF upconverter arrived, with the intent of poking at LF signals. The upconverter circuit board also contains a mostly populated RF noise source:
Being a sucker for noise sources, I spent some time pondering the circuitry.
The as-built board has a 0 Ω jumper instead of the 6 dB pad along the upper right edge:
The previous version had a pi bandpass filter in place of the pad and you could certainly repopulate it with two caps and a teeny inductor if you so desired.
I added the SMA connector, which isn’t quite identical to the IF output connector above it:
That will require a new hole in the end plate that I’ll get around to shortly. It also needs an external switch connected to the Enable jumper, but that’s in the nature of fine tuning.
I’m awaiting a handful of adapters & cables from halfway around the planet…
After the 5 mm white LEDs failed on the original desk lamp rebuild, I picked up some chip-on-board LED lamps from the usual eBay supplier:
The LED’s aluminum baseplate (perhaps there’s an actual “board” inside the yellow silicone fill) is firmly epoxied to a small heatsink from the Big Box o’ Heatsinks, chosen on the basis of being the right size and not being too battered.
The rather limited specs say the LED supply voltage can range from 9 to 12 V, suggesting a bit of slack, with a maximum dissipation of 3 W, which definitely requires a heatsink.
The First Light test looked promising:
That’s driven from the same 12 VDC 200 mA wall wart that I used for the failed ring light version. Measuring the results shows that the supply now runs at the ragged edge of its current rating, with the output voltage around 10.5 V with plenty of ripple:
The 260 mA current (bottom, trace 1 at 100 mA/div) varies from 200 to 300 mA as the voltage (top, trace 2 at 2 V/div) varies between 10 V and a bit under 11 V. If you believe the RMS values, it’s dissipating 2.7 W and the heatsink runs at a pleasant 105 °F in an ordinary room. The wall wart gets about as warm as you’d expect; it contains an old heavy-iron transformer and rectifier, not a trendy switcher.
The heatsink mount looks nice, in a geeky way:
The left side must be that long to anchor the gooseneck; I thought about tapering the slab a bit, but, really, it’s OK the way it is. Dabs of epoxy hold the gooseneck and heatsink in place.
The heatsink rests on a small ledge at the bottom of the slab that’s as tall as the COB LED is thick, with a wire channel from the gooseneck socket:
The Hilbert Curve infill on the top produces a textured finish; I’m a sucker for that pattern.
The old lamp base isn’t particularly stylin’, but the new head lights up my desk below the big monitors without any glare:
Now, let’s see how long this one lasts…
The OpenSCAD source code as a Github gist:
| // Chip-on-board LED light heatsink mount for desk lamp | |
| // Ed Nisley KE4ZNU December 2015 | |
| Layout = "Show"; // Show Build | |
| //- Extrusion parameters must match reality! | |
| ThreadThick = 0.25; | |
| ThreadWidth = 0.40; | |
| HoleWindage = 0.2; | |
| Protrusion = 0.1; // make holes end cleanly | |
| inch = 25.4; | |
| function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit); | |
| //———————- | |
| // Dimensions | |
| ID = 0; // for round things | |
| OD = 1; | |
| LENGTH = 2; | |
| Gooseneck = [3.0,5.0,15.0]; // anchor for end of gooseneck | |
| COB = [25.0,23.0,2.5]; // Chip-on-board LED module | |
| Heatsink = [35.5,31.5,4.0]; // height is solid base bottom | |
| HSWire = [23.0,28.0,53.3]; // anchor width OC, width OAL, length OC | |
| HSWireDia = 1.4; | |
| HSLip = 1.0; // width of lip under heatsink | |
| BaseMargin = 2*2*ThreadWidth; | |
| BaseRadius = Gooseneck[OD]; // 2 x gooseneck = enough anchor, sets slab thickness | |
| BaseSides = 2*4; | |
| Base = [(Gooseneck[LENGTH] + Gooseneck[OD] + Heatsink[0] + 2*BaseRadius + BaseMargin), | |
| (Heatsink[1] + 2*BaseRadius + 2*BaseMargin), | |
| 2*BaseRadius]; | |
| //———————- | |
| // 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, | |
| $fn=Sides); | |
| } | |
| //– Lamp heatsink mount | |
| module Lamp() { | |
| difference() { | |
| translate([(Base[0]/2 – BaseRadius – Gooseneck[LENGTH]),0,0]) | |
| hull() | |
| for (i=[-1,1], j=[-1,1]) | |
| translate([i*(Base[0]/2 – BaseRadius),j*(Base[1]/2 – BaseRadius),Base[2]/2]) | |
| sphere(r=BaseRadius/cos(180/BaseSides),$fn=BaseSides); | |
| translate([(Heatsink[0]/2 + Gooseneck[OD]),0,Heatsink[2] + COB[2]]) // main heatsink recess | |
| scale([1,1,2]) | |
| cube((Heatsink + [HoleWindage,HoleWindage,0.0]),center=true); | |
| translate([(Heatsink[0]/2 + Gooseneck[OD]),0,Heatsink[2] – Protrusion]) // lower lip to shade lamp module | |
| scale([1,1,2]) | |
| cube(Heatsink – [2*HSLip,2*HSLip,0],center=true); | |
| translate([0,0,Base[2]/2]) // goooseneck insertion | |
| rotate([0,-90,0]) rotate(180/8) | |
| PolyCyl(Gooseneck[OD],Base[0],8); | |
| translate([0,0,Base[2]/2 + Gooseneck[ID]/2]) // wire exit | |
| rotate([180,0,0]) | |
| PolyCyl(Gooseneck[ID],Base[2],6); | |
| translate([Gooseneck[OD],0,(COB[2] – Protrusion)/2]) // wire slot | |
| rotate([180,0,0]) | |
| cube([2*Gooseneck[OD],Gooseneck[ID],(COB[2] + Protrusion)],center=true); | |
| } | |
| } | |
| //———————- | |
| // Build it | |
| if (Layout == "Show") { | |
| Lamp(); | |
| } | |
| if (Layout == "Build") { | |
| } |
Well, a picture of my circuitry, anyhow, there in the upper-right corner:
It’s the avalanche noise random number generator:
I’m pretty sure they color-negatived it to suppress that retina-burn magenta PETG holder.
It wasn’t for my column, but the Tinny cover painting for Circuit Cellar Issue 29 (“Measurement and Control”) hangs near my desk:
Back then, I was writing the Firmware Furnace column. Ah, those were the days…
A bag arrived from halfway around the planet, bearing five sets of cheap earbuds. There was no way to tell from the eBay description, but they’re vented on the side:
And also to the rear, down inside those deep slots below the chromed plastic cover:
The raised lettering is a nice touch; the other earbud has a script L.
The PET braid over the fragile wire should withstand a bit more abuse than usual. The strain relief isn’t anything to cheer, though, consisting of that rectangular channel with the wire loose inside. I figured I’d start minimal and fix whatever crops up; I have nine more earbuds to go.
The motivation for all this was having the Gorilla Tape peel off the helmet, leaving a hardened mass of glue behind, then snagging the earbud wires. This is the new, somewhat better protected, wiring:
In a triumph of hope over experience, I applied more Gorilla Tape:
The helmet may need replacing after another iteration or two.
My solid modeling hand has become stronger these days, so I should gimmick up a flat-ish wart anchoring the mic boom and all the wiring to the helmet shell.
While installing Mint on the Lenovo Q150, I discovered that the right button on the (long disused) Logitech M305 wireless mouse wasn’t working. After replacing the batteries (always check the batteries), it still didn’t work, so I peeled the four slippery feet off the bottom, removed the screws, and confronted the interior:
Much to my surprise, the button switches had removable covers:
I put a minute drop of DeoxIT Red on a slip of paper, ran it between both pairs of contacts, removed a considerable amount of tarnish, reassembled in reverse order, and it’s all good again.
The glue on the back of the slippery feet didn’t like being peeled off, so I expect they’ll fall off at some point.
It’s much easier to drive a GUI with three functional buttons…
[Update: Long-time commenter Raj notes:
I always had problem with the middle button. I have replaced them a few times and learnt that they come with different operating pressures. The soft ones are hard to come by. I found an alternate in the PTT switches on Yaesu handies in my junk.
That’s the blocky switch to the left of the shapely wheel cutout.]
After 95 minutes on a pleasant ride with temperature around 55 °F, the STK C battery had 0.59 W·h remaining (dark green trace):
The last time around, it had 1.85 W·h after 61 minutes. Subtracting the two (and ignoring that it may have started with slightly different charges and behave differently at different temperatures) says the camera used 1.26 W·h = 76 W·min in 34 minutes, which averages out to 2.2 W.
That’s close enough to the “a bit over 2 W” figured from those partial-to-empty measurements for me.
The discharge tests from early November:
The best STK battery (D) holds just under 4.2 A·h, so its absolute longest run time could be 110-ish minutes. That graph shows the A cell was just about done after 75 minutes, so changing the battery after an hour still makes sense; you never know what will happen during the last few minutes of a ride…
The Smell of Molten Projects in the Morning 