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
Another stack of proto boards arrived, this time 80×120 mm, and I ran off another pair of holders:
Not wanting to, ahem, screw around with the lathe, the screws got themselves shortened the old-fashioned way: by hand, with the screw cutter, then filed and passed through a 4-40 die to clean up the threads.
Bah!
Having hacked back the end of the USB gooseneck extension, a tweak of the COB LED heatsink mount for my desk lamp produces a smaller version for a 1.8 W LED:
That fits half of a random heatsink, bandsawed just to the far side of the middle fin and milled flat.
Ream out the 5 mm hole with a #8 drill for a snug fit around the gooseneck, jam gooseneck in place, dab epoxy on the corners of the recess, mash the heatsink in place, solder wires to LED, smear epoxy on the aluminum backplate, clamp while curing:
And it looks pretty good, if I do say so myself:
The hook-n-loop tape holding the cable to the bandsaw gotta go, but should suffice until I conjure a better mount.
The alert reader may wonder how a 9 V COB LED runs from a 5 V USB cable with nary a trace of a voltage booster to be seen. Well, that’s not really a USB cable any more; I paralleled the red+white and black+green wires for lower resistance, then hacked a 9 VDC power supply into an old USB hub:
I ripped out the upstream USB plug, hotwired the 9 V supply where the 5 V USB wires used to be, soldered jumpers on the downstream sockets to short the outer two pin pairs together, razor-knifed the power leads going into the epoxy-blobbed USB controller, and declared victory:
Admittedly, that “In Use” LED runs a bit brighter now.
I have a few other tools on that bench in need of LED lights; when I build ’em, they can all plug into this hub. No reason to invent new connectors & cables & all that. It may need a power switch.
Turns your stomach, eh?
The OpenSCAD source code as a GitHub Gist:
| // Chip-on-board LED light heatsink mount for desk lamp | |
| // Ed Nisley KE4ZNU December 2015 | |
| // February 2017 – rectangular COB, smaller heatsink | |
| 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 = [30.0,11.0,2.5]; // Chip-on-board LED module | |
| Heatsink = [37.1,19.2,10.0]; // overall | |
| HeatsinkBase = 2.0; // solid base below fins | |
| HSLip = 1.0; // width of lip under heatsink | |
| BaseMargin = 2*2*ThreadWidth; | |
| BaseRadius = 3*ThreadThick + Gooseneck[OD]/2; // defines slab thickness | |
| BaseSides = 2*4; | |
| Base = [(Gooseneck[LENGTH] + Gooseneck[OD] + Heatsink[0] + 2*BaseRadius + BaseMargin), | |
| (Heatsink[1] + 2*BaseRadius + 2*BaseMargin), | |
| 2*BaseRadius]; | |
| echo(str("Slab thickness: ",Base[2])); | |
| //———————- | |
| // 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]), // main heatsink recess | |
| 0, | |
| (Base[2] + Heatsink[2]/2 – HeatsinkBase)]) | |
| cube((Heatsink + [HoleWindage,HoleWindage,0.0]),center=true); | |
| translate([(Heatsink[0]/2 + Gooseneck[OD]),0,HeatsinkBase]) // 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,(Base[2] – HeatsinkBase – Protrusion)/2]) // wire slot | |
| rotate([180,0,0]) | |
| cube([2*Gooseneck[OD],Gooseneck[ID],(Base[2] – HeatsinkBase + Protrusion)],center=true); | |
| } | |
| } | |
| //———————- | |
| // Build it | |
| if (Layout == "Show") { | |
| Lamp(); | |
| } | |
| if (Layout == "Build") { | |
| } |
The USB gooseneck extension consists of a spring-steel helix with an aluminum filler strip to smooth the outside:
A pin vise holds the intact part of the gooseneck.
The filler unwinds easily, but the spring required several bashes with a drift punch to loosen the first coil. The pin vise can’t apply enough grip to immobilize the spring, so you (well, I) bashed more-or-less radially outward, rather than at a tangent; that’s almost as difficult to do as to describe.
After enough bashing to get a grip with sturdy needlenose pliers, the spring unwound in short sections, again applying force radially to avoid turning the gooseneck in the pin vise:
The black helix aimed off to the side seems to be plastic from the USB shell injection-molded around the connector hardware.
Chopping the spring with the tip of a hardened diagonal cutter (don’t do this with a copper-wire dike!) and bashing the tail ends back around the wire core produced a passable result:
The black thing sticking out beyond the spring seems to be the jacket around the wires.
All the conductors are the same diameter, which isn’t shouldn’t be particularly surprising.
A tiny handful of known-good-quality SMA terminators arrived from eBay:
They’re described as KDI Triangle T187GS SMA Female Terminator, 50Ω, 1W, 0-4GHz. A bit of searching suggests MCE (whoever they are) borged KDI quite a while ago (their website, last updated in 2003, has been lightly vandalized) and a datasheet won’t be forthcoming.
In any event, a NooElec NESDR Mini 2+ radio connected to a dual-band VHF-UHF antenna perched near a window shows this for a local FM station:
Zooming to 5 dB/div:
Installing the terminator at the end of an MCX-to-SMA adapter cable:
Haven’t a clue about those tiny little spikes with the terminator in place, but they don’t line up with any of the high-energy inputs and are, most likely, junk brewed up within the radio. That’s with the RF gain set to 49.6 dB and AGC turned off.
The hardware looks like this:
The MCX connector on the radio isn’t the most durable-looking thing I’ve ever seen, so strapping the adapter cable to the case seems like a Good Idea. You can get an NESDR radio with an SMA connector for about the same price, which I’d have done if were available a while ago.
The terminated input looks to be about -75 dBFS, about 15 dB below the between-station noise, and the carrier tops out around -25 dBFS, for a “dynamic range” of 50 dB. Oddly, that’s just about dead on the maximum dynamic range you can get from the 8 bit RTL2832U demodulator / ADC stuffed inside the NESDR: 8 bits × 6 dB/bit.
It is not obvious to me the signal from a randomly chosen (albeit powerful) FM station should exactly fill the receiver’s dynamic range, particularly without AGC riding herd on the RF gain. Some hardware tinkering seems in order.
The GNU Radio flow graph:
Further results from the SDR-based WWVB receiver:
Seven hours of mid-January RF, tight-zoomed in both frequency and amplitude, from 0350 to 1050 local:
The yellow line of the WWVB carrier comes out 2 ppm high, which means the local oscillator chain is 2 ppm low. We know the WWVB transmitter frequency is exactly 60.000 kHz, translated up by 125 MHz to the N3’s tuning range; you can, ahem, set your clock by it.
The blue band marks the loop antenna + preamp passaband, which isn’t quite centered around 60.000 kHz. Tweaking the mica compression caps just a bit tighter should remedy that situation.
Given that input, a very very tight bandpass filter should isolate the WWVB carrier and then it’s all a matter of fine tuning…
All the blocks for a WWVB receiver, lined up on the attic floor:
The dramatis personae:
The headless Pi connects to the house WLAN through its built-in WiFi link, so I can run the whole mess from the Comfy Chair at my desk through Remmina / VNC.
Recording 24 hours of WWVB shows it works:
The wavy line along the left edge looks like a birdie formed by a local oscillator in the attic, because the frequency varies (inversely) with temperature. It’s probably a signal on the Pi board, rectified by some junction, and translated in-band by some Ham-It-Up harmonic. Whatever.
The other traces come out bar-straight, suggesting that the 0.5 ppm (presumably, per °C) temperature-compensated oscillators along the whole RF chain behave as they should.
There’s a slight frequency shift, on the order of a few parts-per-million, between the absolutely accurate WWVB carrier and the indicated display. Not a big deal.
The broad, albeit irregular, orange band down the middle shows the loop antenna / preamp bandwidth, which is on the order of 2 kHz at -3 dB and a few kilohertz more down to the noise level.
The broad horizontal gashes seem to come from the N3’s on-board hardware AGC reacting to signals far outside the waterfall. Various birdies appear & disappear, even in this limited view, so you can just imagine what’s happening off-screen; anything popping up within the SDR’s tuning range clobbers the gain, which becomes painfully visible when zoomed this far in along both frequency and amplitude. Turning AGC off should stabilize things; perhaps software can tweak the SDR gain based on a very narrowband filter around 60.000 kHz.
The upper half of the waterfall shows decent reception for most of the night. The bottom half shows there’s basically nothing goin’ down during the day, which is about what I’d expect based watching the Alpha Geek Clock for seven years.
In any event, another 24 hours with the AGC turned off looks better:
Various sources still clobber the receiver response, but it’s not quite so dramatic.
X10 control from the two HR12A remotes got much worse over the last few months and eventually failed completely, which meant I had to actually walk over to the lights and click the switches. Not to be tolerated, sez I, so I would walk to the bedroom and poke the appropriate buttons on the wired controller (long since obsolete) by the bed. That worked perfectly, which eventually convinced me to dismantle the TM 751 transceiver.
It’s not good when soot plates the case:
I like how they capacitively coupled RF from the antenna for complete line-voltage isolation.
The PCB looked like it got rather hot over there on the left side:
A Zener diode on the component side of the PCB looked a bit toasty, so I decided this gadget had passed its best-used-by-date and dropped it in the electronics recycling box (after harvesting the antenna, just in case).
A new-in-box TM 751 from eBay arrived a few days ago and works just fine.
Done!
The Smell of Molten Projects in the Morning 