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.
Making the world a better place, one piece at a time
There being nothing like a new problem to take your mind off all your old problems, now there’s a cable tie latch recess:
A sectioned view of the model shows the layout:
On the other side, a ramp helps bend the tie toward the MPCNC rail:
Which looks thusly in the realm of applied mathematics:
I’ll leave the OpenSCAD code to your imagination, because the endstop block turns out to be a bit small for the recesses. Eventually, they need a dust cover and some cleanup.
So, there!
As part of some protracted flailing around while trying to get GNU Radio running on a Raspberry Pi 3, I discovered Raspbian defaults to a 100 MB swap file, rather than a swap partition, and everything I thought I knew about swap management seems inoperative. The key hint came from some notes on gr-gsm installation.
Tweak the /etc/dphys-swapfile config file to set CONF_SWAPFACTOR=2 for a 2 GB swap file = twice the size of the Pi’s 1 GB memory.
Start it up:
sudo dphys-swapfile swapoff sudo dphys-swapfile setup sudo dphys-swapfile swapon
And verify it worked:
cat /proc/meminfo MemTotal: 949580 kB MemFree: 194560 kB MemAvailable: 594460 kB Buffers: 85684 kB Cached: 377276 kB SwapCached: 0 kB Active: 600332 kB Inactive: 104668 kB Active(anon): 250408 kB Inactive(anon): 20688 kB Active(file): 349924 kB Inactive(file): 83980 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 1918972 kB SwapFree: 1918972 kB Dirty: 40 kB Writeback: 0 kB AnonPages: 242072 kB Mapped: 136072 kB Shmem: 29060 kB Slab: 33992 kB SReclaimable: 22104 kB SUnreclaim: 11888 kB KernelStack: 1728 kB PageTables: 3488 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 2393760 kB Committed_AS: 947048 kB VmallocTotal: 1114112 kB VmallocUsed: 0 kB VmallocChunk: 0 kB CmaTotal: 8192 kB CmaFree: 6796 kB
Then it became possible to continue flailing …
A pair of known-good MicroSD cards arrived direct from Samsung at a surprisingly slight premium over the junk available on Amazon:
f3probe reported they’re OK, which is no surprise:
sudo f3probe --time-ops /dev/sdc
F3 probe 6.0
Copyright (C) 2010 Digirati Internet LTDA.
This is free software; see the source for copying conditions.
WARNING: Probing normally takes from a few seconds to 15 minutes, but
it can take longer. Please be patient.
Probe finished, recovering blocks... Done
Good news: The device `/dev/sdc' is the real thing
Device geometry:
*Usable* size: 29.81 GB (62521344 blocks)
Announced size: 29.81 GB (62521344 blocks)
Module: 32.00 GB (2^35 Bytes)
Approximate cache size: 0.00 Byte (0 blocks), need-reset=no
Physical block size: 512.00 Byte (2^9 Bytes)
Probe time: 2'04"
Operation: total time / count = avg time
Read: 51.79s / 4197134 = 12us
Write: 1'10" / 4192321 = 16us
Reset: 1.41s / 1 = 1.41s
These will go into Raspberry Pi projects, where their huge capacity won’t produce any benefit. It seems one can’t get known-good, small cards these days.
I don’t see much point in buying known-crap counterfeits on Amazon, given their commingled-storage problem as pointed out by their helpful FBA advice:
Use the manufacturer barcode to track inventory
By default, your seller account is set to use the manufacturer barcode to track your eligible inventory throughout the Amazon fulfillment process. You can change this default barcode preference at any time. You have the option to change your barcode preference for each offer you create. You can also change your barcode preference for a product when you change a listing from Fulfilled by Merchant to Fulfilled by Amazon.
Important: Items in your inventory that are identified and tracked using manufacturer barcodes are commingled with items of the same products from other sellers who also use manufacturer barcodes for those items.
If you choose to use manufacturer barcodes, when customers purchase a product from you, Amazon can send the item that is closest to them, even if you didn’t send it to the fulfillment center. When that happens, you get the credit for the sale, and we transfer an item from your inventory to the seller whose inventory was used to fulfill the order. In addition, if you use the manufacturer barcode, you don’t have to apply an Amazon barcode to each item yourself.
Even though inventory tracked using the manufacturer barcode is commingled within the network, the source of the inventory is tracked by our fulfillment systems and is taken into consideration if inventory problems arise.
The Protoneer Arduino CNC shield (*) has a row of 2-pin headers for bare endstop switches. Being a big fan of LED Blinkiness, I have a stock of 3-pin Makerbot-style mechanical endstops that require a +5 V connection in addition to ground and the output.
A crude-but-effective adapter consists of half a dozen header pins soldered to a length of stout copper wire, with a pigtail to a +5 V pin elsewhere on the board:
A closer look:
The pins get trimmed on the other side of the bus wire, because they don’t go through the PCB.
Installed on the board, it doesn’t look like much:
Looks like it needs either Kapton tape or epoxy, doesn’t it?
Three more endstops at the far end of the MPCNC rails (for hard limits) will fill the unused header pins.
(*) It’s significantly more expensive than the Chinese knockoffs, but in this case I cheerfully pay to support the guy: good stuff, direct from the source.
The folks I’ve been coaching through their plotter build project showed it off at the local MiniMakerFaire this past weekend. Next time around, I’ll insist they secure their circuit boards and use good wiring techniques, so as to avoid destroying more stepper drivers.
To that end, adding mounting holes to my proto board holder seems in order:
The board dimensions now live in an associative array, so you just pick the board name from a Configurator drop-down list:
/* [Options] */ PCBSelect = "ArdUno"; // ["20x80","40x60","30x70","50x70","70x90","80x120","ArdDuemil","ArdMega","ArdPro","ArdUno","ProtoneerCNC"] PCB_NAME = 0; PCB_DIMENSION = 1; PCBSizes = [ ["40x60",[40,60,1.6]], ["30x70",[30,70,1.6]], ["50x70",[50,70,1.6]], ["20x80",[20,80,1.6]], ["70x90",[70,90,1.6]], ["80x120",[80,120,1.6]], ["ArdDuemil",[69,84,1.6]], ["ArdMega",[102,53.5,1.6]], ["ArdPro",[53,53.5,1.6]], ["ArdUno",[69,53.1,1.6]], ["ProtoneerCNC",[69,53.1,1.6]], ];
Which seems easier than keeping track of the dimensions in comments.
You can now put the PCB clamp screws and mounting holes on specific corners & sides, allowing oddball locations for Arduino boards with corner cutouts along the right edge:
A “selector” notation separates the hole location from the board dimensions & coordinates:
ScrewSites = [ // [-1,1],[1,1],[1,-1],[-1,-1], // corners // [-1,0],[1,0],[0,1],[0,-1] // middles [-1,1],[-1,-1],[1,0] // Arduinos ];
Might not be most obvious way, but it works for me. Most of the time, corner clamps seem just fine, so I’m not sure adding the clamp and mounting hole locations to the dimension array makes sense.
The OpenSCAD source code as a GitHub Gist:
| // Test support frame for proto boards | |
| // Ed Nisley KE4ZNU – Jan 2017 | |
| // June 2017 – Add side-mount bracket, inserts into bottom | |
| // 2017-11 – Selectable board sizes, chassis mounting holes | |
| /* [Options] */ | |
| PCBSelect = "ArdUno"; // ["20×80","40×60","30×70","50×70","70×90","80×120","ArdDuemil","ArdMega","ArdPro","ArdUno","ProtoneerCNC"] | |
| Layout = "Frame"; // [Frame, Bracket] | |
| ClampFlange = true; // external flange | |
| Mounts = true; // frame to chassis screw holes | |
| Channel = false; // wiring channel cutout | |
| WasherRecess = false; // cutout around screw head | |
| /* [Extrusion parameters] */ | |
| ThreadThick = 0.25; // [0.15, 0.20, 0.25] | |
| ThreadWidth = 0.40; | |
| function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit); | |
| /* [Hidden] */ | |
| Protrusion = 0.1; | |
| HoleWindage = 0.2; | |
| inch = 25.4; | |
| Tap4_40 = 0.089 * inch; | |
| Clear4_40 = 0.110 * inch; | |
| Head4_40 = 0.211 * inch; | |
| Head4_40Thick = 0.065 * inch; | |
| Nut4_40Dia = 0.228 * inch; | |
| Nut4_40Thick = 0.086 * inch; | |
| Washer4_40OD = 0.270 * inch; | |
| Washer4_40ID = 0.123 * inch; | |
| Tap6_32 = 0.106 * inch; | |
| Clear6_32 = 0.166 * inch; | |
| Head6_32 = 0.251 * inch; | |
| Head6_32Thick = 0.097 * inch; | |
| Nut6_32Dia = 0.312 * inch; | |
| Nut6_32Thick = 0.109 * inch; | |
| Washer6_32OD = 0.361 * inch; | |
| Washer6_32ID = 0.156 * inch; | |
| ID = 0; | |
| OD = 1; | |
| LENGTH = 2; | |
| //- PCB sizes | |
| // the list must contain all the selection names as above | |
| //* [Hidden] */ | |
| PCB_NAME = 0; | |
| PCB_DIMENSION = 1; | |
| PCBSizes = [ | |
| ["40×60",[40,60,1.6]], | |
| ["30×70",[30,70,1.6]], | |
| ["50×70",[50,70,1.6]], | |
| ["20×80",[20,80,1.6]], | |
| ["70×90",[70,90,1.6]], | |
| ["80×120",[80,120,1.6]], | |
| ["ArdDuemil",[69,84,1.6]], | |
| ["ArdMega",[102,53.5,1.6]], | |
| ["ArdPro",[53,53.5,1.6]], | |
| ["ArdUno",[69,53.1,1.6]], | |
| ["ProtoneerCNC",[69,53.1,1.6]], | |
| ]; | |
| PCBIndex = search([PCBSelect],PCBSizes)[0]; | |
| PCBSize = PCBSizes[PCBIndex][PCB_DIMENSION]; | |
| //echo(str("PCB Size Table: ",PCBSizes)); | |
| //echo(str("PCB Select: ",PCBSelect)); | |
| //echo(str("PCB Index: ",PCBIndex)); | |
| echo(str("PCB Size: ",PCBSize)); | |
| /* [Sizes] */ | |
| WallThick = 4.0; // basic frame structure | |
| FrameHeight = 10.0; | |
| /* [Hidden] */ | |
| Insert = [3.9,4.6,5.8]; | |
| PCBShelf = 1.0; // width of support rim under PCB | |
| Clearance = 1*[ThreadWidth,ThreadWidth,0]; // around PCB on all sides | |
| ScrewOffset = ThreadWidth + Insert[OD]/2; // beyond PCB edges | |
| echo(str("Screw offset: ",ScrewOffset)); | |
| /* [Screw Selectors] */ | |
| // ij selectors for PCB clamp screw holes: -1/0/1 = left/center/right , bottom/center/top | |
| ScrewSites = [ | |
| // [-1,1],[1,1],[1,-1],[-1,-1], // corners | |
| // [-1,0],[1,0],[0,1],[0,-1] // middles | |
| [-1,1],[-1,-1],[1,0] // Arduinos | |
| ]; | |
| // ij selectors for frame mounting holes | |
| MountSites = [ | |
| [0,-1],[0,1], | |
| // [-1,0],[1,0] | |
| ]; | |
| function ScrewAngle(ij) = (ij[0]*ij[1]) ? ij[0]*ij[1]*15 : ((!ij[1]) ? 30 : 0); // align screw sides | |
| OAHeight = FrameHeight + Clearance[2] + PCBSize[2]; // total frame height | |
| echo(str("OAH: ",OAHeight)); | |
| BossOD = 2*Washer4_40OD; // make bosses oversized for washers | |
| FlangeExtension = 4.0 + Washer6_32OD/2 – WallThick; // beyond frame structure | |
| FlangeThick = IntegerMultiple(2.0,ThreadThick); // plate under frame | |
| Flange = PCBSize | |
| + 2*[ScrewOffset,ScrewOffset,0] | |
| + [BossOD,BossOD,0] | |
| + [2*FlangeExtension,2*FlangeExtension,(FlangeThick – PCBSize[2])] | |
| ; | |
| FlangeRadius = BossOD/4; | |
| echo(str("Flange: ",Flange)); | |
| NumSides = 4*5; | |
| WireChannel = [Flange[0],15.0,3.0 + PCBSize[2]]; // ad-hoc wiring cutout | |
| WireChannelOffset = [ | |
| Flange[0]/2,0,(FrameHeight + PCBSize[2] – WireChannel[2]/2) | |
| ]; | |
| //- Adjust hole diameter to make the size come out right | |
| module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes | |
| Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2); | |
| FiiDia = Dia / cos(180/Sides); | |
| cylinder(r=(FiiDia + HoleWindage)/2,h=Height,$fn=Sides); | |
| } | |
| //- Build things | |
| if (Layout == "Frame") | |
| difference() { | |
| union() { // body block | |
| translate([0,0,OAHeight/2]) | |
| cube(PCBSize + Clearance + [2*WallThick,2*WallThick,FrameHeight],center=true); | |
| for (ij = ScrewSites) // screw bosses | |
| if (ij[0] != 0 || ij[1] != 0) | |
| translate([ij[0]*(PCBSize[0]/2 + ScrewOffset), | |
| ij[1]*(PCBSize[1]/2 + ScrewOffset), | |
| 0]) | |
| cylinder(d=BossOD,h=OAHeight,$fn=NumSides); | |
| if (ClampFlange) // flange for work holder & mounting screw holes | |
| linear_extrude(height=Flange[2]) | |
| hull() | |
| for (i=[-1,1], j=[-1,1]) { | |
| translate([i*(Flange[0]/2 – FlangeRadius),j*(Flange[1]/2 – FlangeRadius)]) | |
| circle(r=FlangeRadius,$fn=NumSides); // convenient rounding size | |
| } | |
| } | |
| for (ij = ScrewSites) { // screw position indeies | |
| if (ij[0] != 0 || ij[1] != 0) { | |
| translate([ij[0]*(PCBSize[0]/2 + ScrewOffset), | |
| ij[1]*(PCBSize[1]/2 + ScrewOffset), | |
| -Protrusion]) | |
| rotate(ScrewAngle(ij)) | |
| PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6); // screw clearance holes | |
| translate([ij[0]*(PCBSize[0]/2 + ScrewOffset), | |
| ij[1]*(PCBSize[1]/2 + ScrewOffset), | |
| -Protrusion]) | |
| rotate(ScrewAngle(ij)) | |
| PolyCyl(Insert[OD],OAHeight – PCBSize[2] – 3*ThreadThick + Protrusion,6); // inserts | |
| if (WasherRecess) | |
| translate([ij[0]*(PCBSize[0]/2 + ScrewOffset), | |
| ij[1]*(PCBSize[1]/2 + ScrewOffset), | |
| OAHeight – PCBSize[2]]) | |
| PolyCyl(1.2*Washer4_40OD,(PCBSize[2] + Protrusion),NumSides); // optional washer recess | |
| } | |
| } | |
| if (Mounts) | |
| for (ij = MountSites) | |
| translate([ij[0]*(Flange[0]/2 – Washer6_32OD/2),ij[1]*(Flange[1]/2 – Washer6_32OD/2),-Protrusion]) | |
| rotate(ScrewAngle(ij)) | |
| PolyCyl(Clear6_32,(Flange[2] + 2*Protrusion),6); | |
| translate([0,0,OAHeight/2]) // through hole below PCB | |
| cube(PCBSize – 2*[PCBShelf,PCBShelf,0] + [0,0,2*OAHeight],center=true); | |
| translate([0,0,(OAHeight – (PCBSize[2] + Clearance[2])/2 + Protrusion/2)]) // PCB pocket on top | |
| cube(PCBSize + Clearance + [0,0,Protrusion],center=true); | |
| if (Channel) | |
| translate(WireChannelOffset) // opening for wires from bottom side | |
| cube(WireChannel + [0,0,Protrusion],center=true); | |
| } | |
| // Add-on bracket to hold smaller PCB upright at edge | |
| PCB2Insert = [3.0,4.9,4.1]; | |
| PCB2OC = 45.0; | |
| if (Layout == "Bracket") | |
| difference() { | |
| hull() // frame body block | |
| for (i=[-1,1]) // bosses around screws | |
| translate([i*(PCBSize[0]/2 + ScrewOffset),0,0]) | |
| cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides); | |
| for (i=[-1,1]) // frame screw holes | |
| translate([i*(PCBSize[0]/2 + ScrewOffset),0,-Protrusion]) | |
| rotate(i*180/(2*6)) | |
| PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6); | |
| for (i=[-1,1]) // PCB insert holes | |
| translate([i*PCB2OC/2,(Washer4_40OD + Protrusion),OAHeight/2]) | |
| rotate([90,0,0]) | |
| cylinder(d=PCB2Insert[OD],h=2*(Washer4_40OD + Protrusion),$fn=6); | |
| } | |
The previous times we slow-roasted a pork shoulder, the smoke alarm went off well before the skin crisped. We’d drained the drippings from the pan before crisping the skin, but the residue still smoked up a storm; this time we we left the pool in place to see if it kept the surface cooler and reduced the smoke.
Well, no, it didn’t. This happened in the five minutes between one rotation and the next:
Knowing things would get at least a little smoky, I’d closed the pocket door (on the left) and hung a beach towel across the opening into the laundry room (to the right), which kept most of the smoke out of the rest of the house. The smoke detector in the laundry room didn’t go off until I walked through the towel, so my precautions worked pretty well.
Wow, was that skin crispy:
Plenty of smoke and no fire; the roasting pan has narrow slits for that very reason. Took a couple of hours to vent the house, during which the yard smelled downright yummy.
Next time, we’ll plunk the roast on a lined cookie sheet (with a rim!) and see what happens.
Some early morning data from the WWVB preamp with the 60 kHz tuning fork resonator filter in full effect (clicky for more dots):
The dotted line comes from WWVB’s 1 Hz PWM (-ish) modulation: yeah, it works!
The filter cuts out the extraneous RF around the WWVB signal, as compared with a previous waterfall and some truly ugly hash:
Well, not quite all the hash. Enabling the SDR’s hardware AGC and zooming out a bit reveals some strong birdies:
The big spike over on the left at 125.000 MHz comes from the Ham-It-Up local oscillator. A series of harmonics starting suspiciously close to 125.032768 kHz produces the one at 125.066 MHz, just to the right of the WWVB signal, which leads me to suspect a rogue RTC in the attic.
There is, in fact, a free running “Test Signal Source” on the Ham-It-Up board:
Although I have nary a clue about that bad boy’s frequency, measuring it and cutting the inverter’s power trace / grounding the cap may be in order.
The SDR’s AGC contributes about 30 dB of gain, compresses the hottest signals at -25 dB, and raises those harmonics out of the grass, so it’s not an unalloyed benefit. Manually cranking on 10 dB seems better:
The bump in the middle shows the WWVB preamp’s 2 kHz bandwidth around the 60 kHz filter output, so the receiver isn’t horribly compressed. The carrier rises 30 dB over that lump, in reasonable agreement with the manual measurements over a much narrower bandwidth:
With all that in mind, a bit of careful tweaking produces a nice picture:
I love it when a plan comes together …
The Smell of Molten Projects in the Morning 